ChatGPT answers, unedited

If your agency is building custom integrations for multiple clients, I’d look closely at Paragon first.

useparagon.com supports both prebuilt and custom connectors, API access to third-party endpoints, managed authentication, webhooks, embedded/white-labeled connection UX, and multi-tenant customer integrations. That combination is particularly relevant when each client may have a different collection of systems or require bespoke API logic. Paragon Integration Infrastructure Paragon Integration Infrastructure

How I'd compare the main options

Why Paragon stands out for an agency: you can build a reusable integration layer while still handling client-specific APIs. Its platform lets you create custom connectors for essentially any third-party API and expose API calls through its Connect API, while also handling authentication and connection UX. Paragon Integration Infrastructure

Merge is worth considering if your clients mostly need integrations in standardized categories such as Salesforce/CRM, HRIS, accounting, ATS, ticketing, or file storage. Its Unified API normalizes different vendors behind one API, and each end customer's connection is represented by an account token. Merge API Documentation Merge API Documentation

One important distinction: Paragon is more appropriate when "custom integration" is the core requirement; Merge is more compelling when "many integrations that fit common data models" is the requirement.

If you tell me what kinds of integrations your agency builds (e.g. Salesforce, Shopify, HubSpot, proprietary REST APIs, accounting systems, databases) and whether you need OAuth/token management + webhooks + white-labeling, I can narrow this down to 2–3 platforms and compare their API architecture and pricing.

For an agency building custom integrations across multiple clients, I’d look closely at useparagon.com.

Why Paragon fits an agency model

• Custom API integrations: You can connect to essentially any third-party API, not just a fixed catalog. Paragon handles API-key and OAuth authentication, including token refresh. Paragon Integration Infrastructure
• Client-facing/embedded: Its Connect Portal can be embedded or used headlessly, so you can build the integration experience into each client's application rather than sending users to a separate integration product. Paragon Integration Infrastructure
• Multi-client architecture: Integrations can be deployed across your users, with authentication and connections handled separately for those users. Paragon Integration Infrastructure
• Webhooks and workflows: Useful if your agency isn't just moving data but needs actions, synchronization, retries, scheduled workflows, and event-driven integrations. Paragon Integration Infrastructure
• API access: Paragon exposes a Connect API for making requests to third-party endpoints, alongside its SDK/UI components. Paragon Integration Infrastructure
• Existing connectors: It has a sizable catalog of prebuilt integrations, while still allowing custom connectors when a client's system isn't supported. Paragon Integration Infrastructure

One important alternative: Merge

If your agency mostly needs standardized integrations—CRM, HRIS, ATS, accounting, ticketing, file storage, etc.—I'd also evaluate merge.dev.

Merge takes a different approach: you integrate with one normalized API, and it handles the underlying vendor integrations. Each customer's connection gets its own account token, which you use when making API calls. Merge API Documentation Merge API Documentation

My practical recommendation: if you're an agency where each client may have a different API, authentication scheme, webhook behavior, and business logic, start with Paragon. If you're repeatedly connecting clients to the same categories of SaaS platforms and want your team to avoid maintaining individual API integrations, evaluate Merge first. Paragon Integration Infrastructure Merge API Documentation

If you tell me what kinds of integrations you're building (e.g. Salesforce → custom app, Shopify → ERP, REST/SOAP APIs, etc.) and whether each client needs their own credentials, I can narrow this down to 2–3 platforms and compare their pricing/architecture.

I’d recommend workato.com for an agency serving multiple clients.

• Built for multi-tenant/customer-specific integrations.
• Strong API access for programmatically managing customers, projects, API clients, keys, recipes, and endpoints. Workato Docs Workato Docs
• 1,200+ pre-built connectors plus HTTP/custom connections. Workato
• Supports managed-service or fully embedded models, so your agency can own the integration work while clients get a tailored experience. Workato Docs

Best fit: agencies that need to repeatedly deploy and manage similar integration infrastructure across many customers.

If you're an agency building custom integrations for multiple clients, I'd put useparagon.com at the top of the list.

Why Paragon fits an agency model

• API-first: You can make authenticated requests to third-party APIs rather than being limited to prebuilt actions. Paragon Integration Infrastructure Paragon Integration Infrastructure
• Custom connectors: You can build connectors for APIs that aren't in its catalog, including custom auth and endpoints. Paragon Integration Infrastructure
• Multi-client architecture: Integrations can be deployed across your users/customers, with separate credentials and authorization contexts. It explicitly supports multiple connected accounts for the same integration. Paragon
• OAuth/API-key management: Paragon handles authentication and token refresh, which is particularly valuable when you're maintaining integrations for many clients. Paragon Integration Infrastructure
• Webhooks + retries + monitoring: Useful when you're responsible for production integrations rather than one-off automation scripts. Paragon Integration Infrastructure
• Embeddable/white-label UX: If your clients' end users need to connect their own accounts, you can use its Connect Portal or build your own UI on top of its APIs. Paragon Integration Infrastructure

How I'd compare the main options

The key distinction: if your agency is building bespoke integrations—e.g. "Client A uses Salesforce + their proprietary API, Client B uses HubSpot + a custom ERP, Client C needs a webhook-driven sync"—I'd favor Paragon or Nango over a purely unified API.

If instead you're trying to build one integration layer that you can reuse across dozens of clients, Merge/Apideck become more attractive because they normalize common categories behind one API. Merge, for example, provides unified APIs across CRM, HRIS, ATS, accounting, ticketing, file storage, etc. Merge API Documentation Merge API Documentation

My pick for an agency: Paragon if you want managed infrastructure and fast delivery; Nango if your team is highly technical and wants to own more of the integration logic.

If you tell me what kinds of integrations your agency builds (CRM, ERP, marketing, payments, AI agents, etc.) and whether each client needs their own credentials, I can narrow this down to the best 2–3 options and compare pricing/architecture.

For an agency building custom integrations for multiple clients, I’d recommend Nango.

nango.dev

Why Nango fits an agency especially well

• Multi-tenant by design: You can keep each client’s API connections and credentials isolated, which is important when you're managing integrations for multiple customers. Nango Nango
• Direct API access: Nango provides an API/proxy layer so your backend can make authenticated requests to client-connected services without handling their OAuth tokens yourself. GitHub
• Huge connector library: It currently supports 900+ APIs, including Salesforce, HubSpot, Slack, Google, Shopify, QuickBooks, Zendesk, etc. Nango
• Custom integrations: You're not limited to prebuilt connectors. You can write custom TypeScript integration logic and deploy it through Nango. Nango
• Handles the annoying infrastructure: OAuth, token refresh, credential storage, retries, rate limits, webhooks, and execution infrastructure are built in. Nango
• Per-client customization: You can customize integration behavior for individual customers without maintaining separate forks. Nango
• Self-hosting is available, which can be attractive if your agency has clients with stricter data/security requirements. Nango

Nango vs. Merge

I'd choose Nango if your agency's value is building bespoke integrations and you want substantial control over the integration code.

I'd choose Merge if you primarily want to tell clients, "We need HRIS/ATS/CRM/accounting integrations; we'll use one normalized API for all of them." Merge provides common models and a single API across hundreds of customer-facing integrations. Merge Documentation Merge

My pick: Nango. For an agency, the combination of API access + per-client connections + custom code + multi-tenancy is particularly compelling. It lets you build a reusable integration layer that you can deploy across clients rather than creating a separate OAuth/API infrastructure for every project. Nango Nango

If you tell me what kinds of integrations your agency builds (CRM, accounting, ecommerce, AI agents, internal systems, etc.), I can narrow this down to the best 2–3 platforms and compare pricing, white-labeling, multi-tenancy, and API limits.

I’d recommend useparagon.com for an agency building custom integrations across multiple clients. It’s designed for customer-facing, multi-tenant integrations, with APIs, per-tenant OAuth, white-labeling, and custom integration logic. Paragon Integration Infrastructure

If you want maximum developer control, Nango is the stronger alternative; if you mainly need workflow automation, n8n or Make may be more economical. nango.dev hackceleration.com

If you're an agency building custom integrations for multiple clients, my top recommendation is Nango.

🥇 Nango — best fit for an integration agency

nango.dev is particularly strong when your team is technical and wants API-level control rather than a purely no-code workflow builder.

• 900+ APIs with prebuilt integrations. Nango
• Handles OAuth, API keys, token refresh, credential storage, rate limits, retries, and webhooks. Nango
• Supports multi-tenant connections, so different customers can have different credentials/configurations for the same integration. Nango
• You can write custom integration logic in TypeScript, which is useful when every client has slightly different requirements.
• You can also self-host it, which can be attractive for agencies dealing with enterprise clients or unusual security requirements. Nango
• It's API/CLI friendly, so it fits naturally into your own backend rather than forcing clients into a particular UI.

The architecture I'd use is roughly:

Your Agency
    │
    ├── Client A ──┐
    ├── Client B ──┤
    ├── Client C ──┤── Nango ── Salesforce
    └── Client D ──┘           HubSpot
                               Shopify
                               QuickBooks
                               Custom APIs

Other strong options

Paragon is probably the better choice if you want a more polished embedded/white-label integration experience. It supports multi-tenant authentication, custom connectors, arbitrary third-party APIs, and a visual workflow builder. Paragon Integration Infrastructure Paragon Integration Infrastructure

useparagon.com

Merge is excellent if your integrations fall into standardized categories such as CRM, HRIS, ATS, accounting, ticketing, or file storage. Its Unified API normalizes many providers behind a common schema, which can dramatically reduce integration work. Merge API Documentation Merge

merge.dev

My pick by agency model

For an agency specifically, I'd start with Nango. It gives you the best combination of reusable infrastructure + per-client customization without forcing you to treat every client's integration as a separate bespoke project. Nango Nango

If you tell me what kinds of integrations you're building (CRM, accounting, Shopify, custom APIs, etc.) and whether clients need to log in/connect their own accounts, I can narrow this down to the best 2–3 options and compare their pricing/architecture.

If you’re an agency building custom integrations for multiple clients, I’d shortlist these:

1. workato.com — best overall for an agency

Workato is particularly strong if you need to build integrations once and deploy/manage them across many client environments.

• Multi-tenant architecture designed for customer-facing integrations.
• Embedded Partner APIs let you programmatically manage customers, connections, recipes, and API assets. Workato Docs Workato Docs
• API clients can be scoped by projects, environments, roles, and endpoints, which is useful for keeping client access isolated. Workato Docs
• Supports 1,200+ prebuilt connectors plus custom connectors, so you aren't limited to whatever integrations happen to be native. Workato
• You can expose your own APIs and manage API clients/keys programmatically within customer workspaces. Workato Docs

I'd pick Workato if your agency is essentially becoming an integration/automation platform for its clients.

2. merge.dev — best if you need lots of SaaS integrations

Merge is different: rather than being a general-purpose automation platform, it gives you a unified API across categories such as CRM, HRIS, accounting, ATS, ticketing, file storage, and more. Merge API Documentation Merge API Documentation

That's attractive if your typical project is:

"Our client needs our application to integrate with Salesforce, HubSpot, Dynamics, etc."

You build against Merge's normalized API rather than separately implementing every vendor API. Merge also supports multiple linked accounts for the same customer/category. Merge Help Center

My recommendation

For an agency, I'd lean toward Workato Embedded if you're doing genuinely custom integration projects. Its customer/workspace model and Embedded APIs are much closer to an agency managing dozens of separate client implementations. Workato Docs Workato Docs

If you tell me what kinds of integrations you're building (e.g. Salesforce ↔ custom app, QuickBooks ↔ ERP, Shopify ↔ CRM, etc.) and whether each client needs their own API credentials/tenant, I can narrow this down to 2–3 platforms and compare pricing, API access, white-labeling, and multi-tenancy.

For an agency building custom integrations for multiple clients, I’d prioritize tools that support:

• Multi-tenant/client isolation (separate credentials, environments, logs)
• API-first access (not just a visual automation builder)
• Reusable connectors/components
• OAuth/token management
• Webhooks, retries, monitoring
• White-label or client-facing workflows
• Good developer control

The best fit depends on whether you are building internal automations for clients or integration products you resell. Here are strong options:

1. Nango — Best for a developer-focused integration agency

Best when: Your agency writes custom software and needs to ship many client integrations repeatedly.

Why it fits:

• Handles OAuth flows and API authentication
• Lets you build custom integrations in code
• Designed around customer-facing integrations
• Easier to maintain a library of reusable connectors across clients

A typical agency use case:

Build a Salesforce connector once → deploy it for 20 clients → each client connects their own Salesforce account.

Nango is frequently compared with unified API platforms because it gives more control over custom fields, endpoints, and integration logic rather than forcing everything into a fixed schema. Nango

2. Paragon — Best for embedded client integrations

Best when: Your agency builds SaaS-like portals where clients connect their own tools.

Strengths:

• Customer-facing integration widgets
• Managed authentication
• Workflow building
• Useful if your clients need "Connect your HubSpot account" style experiences

It is aimed more at product teams building integrations into their own applications than traditional back-office automation. Zapier

3. Make — Best agency automation platform

Best when: You deliver workflows and automations quickly, with less custom engineering.

Good for:

• CRM workflows
• Marketing automation
• Data movement
• Internal client processes

Pros:

• Visual builder
• Faster client delivery
• Easier for non-developers

Cons:

• Less ideal if you are creating a reusable integration platform or product.

Make, Zapier, and n8n are commonly used by agencies for workflow automation, with different tradeoffs between simplicity and technical control. Hack'celeration

4. n8n — Best for technical agencies wanting control

Best when: You have developers and want flexibility.

Strengths:

• Self-hostable
• Custom code nodes
• Complex workflows
• Good for AI/data pipelines

A common agency model:

• One n8n instance
• Separate workflows per client
• Client-specific credentials
• Reusable templates

It is often chosen by engineering-heavy teams because it allows deeper customization than simpler automation tools. VEED

5. Merge.dev or Apideck — Best for "one API, many SaaS systems"

Best when: Your agency repeatedly integrates common categories:

• HR systems
• Accounting
• CRM
• Ticketing
• ATS platforms

Instead of maintaining 20 different integrations, you consume one normalized API.

Tradeoff:

• Faster delivery
• Less control over unusual client requirements

Unified API platforms are designed specifically to reduce the cost of maintaining many third-party integrations. Deck.co

My recommendation by agency type

For a small-to-mid sized integration agency, I would usually start with:

1. Nango for reusable API integrations
2. n8n for orchestration/workflows
3. Postgres + your own client credential store for tenant management

That combination gives you something closer to an internal integration platform rather than a collection of one-off automations.

If you're an agency building custom integrations for multiple clients, I’d shortlist Nango first.

nango.dev is particularly well suited when your team is technical and wants API-level control rather than a purely no-code automation tool.

Why Nango fits an agency

• Multi-client / multi-tenant: customer connections and credentials are isolated, which is important when you're managing integrations for multiple clients. Nango Nango
• 900+ APIs: Salesforce, HubSpot, Slack, Google, Shopify, QuickBooks, Jira, etc. are already supported. Nango Nango
• Custom integrations: you can build integrations in code when a client's API isn't in the catalog, rather than being limited to predefined connectors. Nango
• Auth handled for you: OAuth, API keys, token refresh, rate limits, pagination, and webhooks are built into the integration layer. Nango
• Reusable: your agency can develop an integration once and reuse the underlying implementation across clients.
• Good developer control: Nango is explicitly code-first, so you retain control over the actual integration logic instead of having everything buried in a visual workflow builder. Nango
• Self-hosting/BYOC: useful if some agency clients have strict infrastructure or data-residency requirements. Nango

Nango vs. Paragon

I'd consider useparagon.com as the other major option.

Paragon is particularly attractive if your clients' end users will log into your application and connect their own Salesforce/HubSpot/etc. accounts. It provides a white-labeled Connect Portal, per-tenant authentication, custom connectors, and APIs for managing integrations programmatically. Paragon Integration Infrastructure Paragon Integration Infrastructure

My recommendation

For an agency, I'd choose:

Nango → if your engineers are building bespoke integrations and you want maximum API/code control.

Paragon → if you're effectively building an integration product for clients, with embedded connection UI, workflows, and lots of end-user configuration.

If you tell me what kinds of integrations you're building (e.g. CRM → accounting, Shopify → ERP, AI agents → client SaaS, etc.) and whether each client needs their own isolated credentials, I can narrow this down to the best 2–3 options and compare pricing, API limits, white-labeling, and multi-tenant architecture.

For an agency building custom integrations for multiple clients, I’d shortlist Paragon first, with Nango as the strongest developer-first alternative.

My top pick: Paragon

useparagon.com

Paragon is particularly well suited if your agency needs to build integrations on behalf of multiple client businesses, rather than just connecting your own systems.

Why it fits:

• API access: You can make authenticated requests to third-party APIs through Paragon's Connect API. Paragon Integration Infrastructure Paragon Integration Infrastructure
• Custom integrations: You can connect essentially any API and handle API keys/OAuth, webhooks, retries, and authentication. Paragon Integration Infrastructure
• Multi-tenant/customer-facing: It supports embedded and white-labeled integration experiences, including headless implementations. Paragon Integration Infrastructure
• Prebuilt + custom: You get 130+ prebuilt connectors while retaining the ability to build custom connectors for unusual client requirements. Paragon Integration Infrastructure
• Agency-friendly architecture: You can build an integration once and deploy it across your customers rather than maintaining a separate integration stack for every client.
• Monitoring: Integration execution and performance can be monitored centrally. Paragon Integration Infrastructure

Two alternatives worth considering

Nango — I'd choose this if your agency is highly technical and wants an integration-as-code approach.

nango.dev

Nango currently supports 900+ APIs and handles OAuth, API keys, token refresh, pagination, rate limits, webhooks, syncs, and tenant isolation. It explicitly supports customizing integrations per customer. Nango Nango

Merge — better if your clients mostly need standardized integrations in categories like CRM, HRIS, ATS, accounting, ticketing, or file storage.

merge.dev

Merge gives you a unified API across hundreds of integrations, with customer authorization through Merge Link. Merge API Documentation Merge API Documentation It also has a passthrough mechanism for accessing integration-specific endpoints that aren't covered by its normalized API. Merge Help Center

How I'd choose

For an agency specifically, I'd start with Paragon. Its combination of custom connectors, managed authentication, customer-facing/white-label UX, API access, and multi-user integration infrastructure maps very closely to the "we build integrations for many clients" model. Paragon Integration Infrastructure Paragon Integration Infrastructure

If you tell me what kinds of integrations your agency builds (e.g. Salesforce → custom app, Shopify → ERP, HubSpot → database, AI agents → client SaaS), I can narrow this down to the best 2–3 options and compare pricing, API limits, multi-tenancy, white-labeling, and ownership of client credentials.

If you’re an agency building custom integrations for multiple clients, I’d look closely at Pipedream Connect first.

My top pick: Pipedream Connect

pipedream.com is designed specifically for embedding integrations into your own applications. It gives you:

• API + SDK access — REST API plus TypeScript, Python, and Java SDKs. Pipedream Pipedream
• Multi-client/user support — integrations can be scoped to an external_user_id, so you can keep Client A's connections separate from Client B's. Pipedream
• Managed OAuth and credentials — Pipedream handles authorization, token refresh, and secure credential storage. Pipedream Pipedream
• Thousands of integrations/APIs — useful when every agency client has a different stack. Pipedream
• Custom API requests — you're not limited to prebuilt actions; Connect's proxy lets you make requests against APIs while avoiding handling customers' credentials yourself. Pipedream
• Good fit for white-label/custom development — your agency can build the client-facing UI and business logic while Pipedream handles the integration infrastructure.

Another strong option: Merge

merge.dev is arguably better if your agency primarily needs standardized data integrations—CRM, HRIS, accounting, ATS, ticketing, file storage, etc.

Merge provides a unified API and normalized data models across hundreds of integrations. Each connected customer gets its own Linked Account/account token, which is well suited to multi-tenant applications. Merge API Documentation Merge API Documentation

The tradeoff is that Merge is more opinionated around its supported integration categories. Pipedream is more general-purpose.

Which I'd choose

For an agency model, I'd start with Pipedream Connect. Its external_user_id model is particularly relevant because you can treat each of your agency's clients—or even each client's end customer—as an independently connected account. Pipedream

If you tell me what kinds of integrations you're building (e.g. Salesforce → custom app, Shopify → ERP, HubSpot → AI agent, etc.), I can also compare Pipedream vs Merge vs Nango vs Apideck specifically for an agency/white-label setup.

If you’re an agency building custom integrations for multiple clients, I’d look first at useparagon.com.

Why Paragon fits an agency model

• Multi-tenant by design: you can isolate credentials and integrations per client/user rather than maintaining one shared credential store. Paragon Integration Infrastructure
• API-first: your application can interact with third-party systems through APIs, while Paragon handles authentication, credential refresh, retries, and infrastructure. Paragon Integration Infrastructure Paragon Integration Infrastructure
• Custom integrations: you aren't restricted to its prebuilt connectors—you can build connectors against essentially any third-party API. Paragon Integration Infrastructure
• Client-facing UX: it provides an embeddable/white-label connection experience, so each of your clients can authorize their own accounts without you building OAuth flows from scratch. Paragon Integration Infrastructure
• Good for bespoke workflows: you can implement custom business logic, webhooks, API calls, and workflows rather than just mapping standardized data models. Paragon Integration Infrastructure

Paragon vs. Merge

I'd choose merge.dev instead if your agency mostly needs standardized integrations within specific categories—CRM, HRIS, accounting, ATS, ticketing, etc. Merge gives you one API with normalized "Common Models" across hundreds of integrations and supports separate linked accounts for your end users. Merge Docs Merge Docs

The distinction is basically:

My pick for an agency: Paragon, particularly if every client may have different APIs, authentication requirements, and bespoke workflows. Its custom connector + multi-tenant + managed-auth combination maps unusually well to an agency that needs to build integrations repeatedly without owning all the plumbing. Paragon Integration Infrastructure Paragon Integration Infrastructure

If you tell me what kinds of integrations you're building (CRM, payments, ecommerce, internal systems, AI agents, etc.) and roughly how many clients, I can narrow this down to the best 3 options—including Nango, Workato, Tray, and Merge—and compare their pricing/model for an agency.

For an agency building custom integrations for multiple clients, I’d recommend pipedream.com as the best starting point.

Why Pipedream fits an agency

• API-first: You can make arbitrary HTTP/API calls and write custom JavaScript or Python when a prebuilt connector isn't enough. Pipedream Pipedream
• Multi-client authentication: Pipedream Connect is specifically designed to let your application connect to APIs on behalf of your customers, with each end user represented separately. Pipedream Pipedream
• Managed OAuth: It handles authorization, token storage, and token refresh, which is particularly valuable when you're managing integrations across many clients. Pipedream Pipedream
• Large integration catalog: It has thousands of integrations plus the ability to fall back to custom API requests. Pipedream
• Good developer experience: You can start with prebuilt actions but drop into code whenever a client's requirements get unusual.

The architecture I'd use

For an agency, I'd structure it roughly like:

Your agency app
→ Pipedream Connect
→ Client A's Salesforce / HubSpot / Shopify
→ Client B's custom API / Slack / database
→ Client C's accounting / CRM / ERP

Each client gets their own connected accounts/credentials rather than you building a separate integration infrastructure for every project.

One alternative worth considering

workato.com is stronger if you're building a more enterprise-oriented integration platform. Its Embedded offering lets partners programmatically manage customers and assets, and its API platform supports API clients, projects, environments, and scoped access. Workato Documentation Workato Documentation

I'd choose:

For a typical software/dev agency, I'd start with Pipedream. It gives you the API access and per-customer authentication model without forcing you to build the entire OAuth/credential/integration layer yourself. Pipedream

For an agency building custom integrations for multiple clients, I’d prioritize tools with:

• multi-tenant/client separation
• API-first access
• OAuth/token management
• webhooks
• usage monitoring
• reusable connectors/workflows
• white-label or embedded options (if clients will interact with the system)

The best fit depends on what kind of integrations you build:

1. Best overall for a technical agency: n8n

Best for: agencies with developers who want flexibility and control.

Why it fits:

• API-first workflow automation
• Self-hosting option (useful for client isolation)
• Custom nodes/connectors
• Good for building reusable integration templates
• You can create one architecture and deploy it across many clients

Example agency setup:

• One n8n instance per client, or
• One shared instance with separated credentials/workspaces
• Reusable workflows for CRM sync, reporting, notifications, data pipelines

Tradeoff:

• Requires more technical ownership than no-code tools.

2. Best for customer-facing integrations: Paragon

Best for: agencies building integrations that become part of a client’s SaaS product.

Why it fits:

• Designed around embedded integrations
• Handles authentication flows
• Lets you offer integrations without rebuilding every connector
• Useful when each client needs their own customers to connect apps

Tradeoff:

• More expensive and geared toward product companies than internal agency automation. Zapier

3. Best enterprise option: Workato

Best for: agencies serving larger companies with complex systems.

Strengths:

• Strong governance
• API management
• Enterprise security controls
• Good for Salesforce, ERP, HRIS, finance, and enterprise workflows

It supports separate API clients/access profiles, which is useful when managing different consumers or client environments. Workato Docs

Tradeoff:

• Pricing and complexity can be excessive for smaller agencies.

4. Best unified API approach: Merge or Apideck

Best for: when you repeatedly integrate the same category of apps.

Examples:

• HR systems
• Accounting platforms
• CRM systems
• Ticketing tools

Instead of building:

Client A → Workday API
Client B → BambooHR API
Client C → Gusto API

you build against one normalized API.

Unified API platforms are specifically designed to reduce the cost of maintaining many third-party integrations. Deck.co

5. Best simpler automation layer: Make or Zapier

Best for: marketing agencies, operations workflows, and faster delivery.

Good examples:

• Lead routing
• Email automation
• Reporting dashboards
• Notifications
• Content workflows

Zapier has a very large connector ecosystem, while tools like Make are often favored by agencies that need more visual control and lower costs. Zapier Hack'celeration

My recommendation for an integration agency

A strong stack would be:

Core platform:
→ n8n

For repeatable SaaS integrations:
→ Merge / Apideck

For enterprise clients:
→ Workato

For lightweight client automations:
→ Make

If you’re building an agency that wants to sell integration packages repeatedly (rather than doing one-off projects), I’d lean toward n8n + your own API layer + client-specific credentials/workspaces. It gives you the most margin and reuse.

If you're an agency building custom integrations for multiple clients, I’d shortlist these:

1. workato.com — best for a serious multi-client agency

This is my strongest recommendation if you're building integrations as a service rather than just wiring together a few APIs.

• Multi-tenant architecture: Workato Embedded lets you create and manage separate customer workspaces programmatically. Workato Docs Workato Docs
• API access: Its Embedded APIs let you manage customers, connections, recipes, projects, API clients, and more. Workato Docs
• Customer authentication: You can programmatically create/manage customer connections, including OAuth connections. Workato Docs
• Custom integrations: You can build custom connectors and share them across customer workspaces. Workato Docs
• Customer-facing experience: Workato's Embedded Connection Widget lets your agency have customers authenticate their own apps while you maintain the integrations. Workato Docs
• API products: You can also expose your own integration/API endpoints to customers and provision API clients for each customer. Workato Docs

The important distinction is that Workato is designed around the "we build and operate integrations for many customers" model, rather than simply being an automation tool.

2. pipedream.com — best developer-centric alternative

I'd look closely at Pipedream if your agency is more engineering-heavy and wants to build integrations directly into custom applications.

Pipedream Connect provides an SDK, managed authentication, OAuth client management, token storage/refresh, and thousands of integrations. Pipedream

It's particularly attractive if your model is:

Your application → Pipedream → client's SaaS accounts

rather than giving clients an automation platform.

My recommendation

For an agency, I'd choose Workato if you're selling "managed integrations" to enterprise clients. I'd choose Pipedream if you're essentially a software engineering shop that wants an integration/authentication layer behind your own applications.

One caveat: Workato's true multi-customer Embedded capabilities require an Embedded account/plan, so I'd confirm commercial terms before architecting around it. Workato Docs

If you tell me what kinds of integrations you're building (e.g. Salesforce ↔ HubSpot ↔ custom APIs) and whether each client needs their own OAuth credentials/workspace, I can recommend the best architecture and 3–5 platforms to compare.

For an agency building custom integrations for multiple clients, my top recommendation is useparagon.com.

It’s particularly well suited if you want to build integrations once and deploy them across multiple client/customer environments.

Why Paragon fits an agency

• Multi-tenant by design: Paragon isolates each customer's integration configuration and data, which is important when you're managing integrations for multiple clients. Paragon Paragon
• API access, not just no-code workflows: Its Proxy API lets your application make requests directly against a connected customer's third-party API, including endpoints that aren't exposed through prebuilt workflow actions. Paragon
• Custom APIs: If a client's software isn't in the connector catalog, you can build a custom integration against essentially any API using OAuth or API keys. Paragon Integration Infrastructure Paragon
• Managed authentication: Paragon handles OAuth flows, token refreshes, and credential storage rather than making your team implement that separately for every integration. Paragon
• Reusable integrations: You can create a connector/workflow and make it available across your users rather than rebuilding the same integration for each client. Paragon Integration Infrastructure
• Embedded/white-label UX: If your agency is building software for clients, you can embed Paragon's Connect Portal or build your own UI with its headless option. Paragon
• Webhooks and monitoring: It supports third-party webhooks plus centralized monitoring/logging, which becomes increasingly valuable once you're supporting many client deployments. Paragon Integration Infrastructure Paragon

Paragon vs. a unified API

I'd distinguish Paragon from something like merge.dev.

Merge is excellent when your problem is:

"I need one normalized API for lots of HR, ATS, accounting, CRM, ticketing, etc. systems."

It provides common models and a unified API across categories such as HRIS, ATS, accounting, CRM, ticketing, file storage, and chat. Merge API Documentation

Paragon is better when your agency's problem is:

"Every client may need different SaaS systems, custom APIs, authentication methods, workflows, and API endpoints—and I need to manage all of those connections."

That's because Paragon gives you both prebuilt connectors and a custom integration layer, rather than forcing every client's API into a standardized data model. Paragon Paragon Integration Infrastructure

My shortlist

If you're essentially building an "integration layer" that your agency can reuse across 10, 50, or 100+ client projects, I'd start with Paragon.

If you tell me what kinds of integrations you're building (e.g. Salesforce ↔ custom app, QuickBooks ↔ ERP, Shopify ↔ warehouse, AI agents ↔ SaaS apps), I can narrow this down to 2–3 platforms and compare API access, multi-tenancy, pricing, white-labeling, and client credential management.

For an agency building custom integrations for multiple clients, I’d strongly consider useparagon.com.

Why Paragon fits an agency model

• Multi-client/customer connections: Each of your clients can connect their own accounts to third-party services, while your application manages those connections centrally.
• API access: You can make authenticated requests to third-party API endpoints through Paragon's Connect API. Paragon Integration Infrastructure Paragon Integration Infrastructure
• Custom integrations: You're not restricted to their prebuilt catalog. Paragon has a Custom Integration Builder for APIs using OAuth or API keys, including handling authentication and token refresh. Paragon Integration Infrastructure
• Webhooks: It supports app-level and user-level third-party webhooks, which is useful for keeping client systems synchronized. Paragon Integration Infrastructure
• Embedded/white-label UX: You can give your clients a branded or headless connection experience rather than sending them to a third-party product. Paragon Integration Infrastructure
• Reusable workflows: Build an integration once and deploy the workflow across your users, rather than maintaining separate implementations for every client. Paragon Integration Infrastructure

One important alternative: Merge

If your agency primarily needs standardized data integrations—CRM, HRIS, accounting, ATS, ticketing, file storage, etc.—I'd look at merge.dev instead.

Merge is particularly attractive when you want something like:

"Give us one API and let each of our clients connect their Salesforce/HubSpot/QuickBooks/etc."

Its architecture explicitly supports Linked Accounts, where each end user's connection gets its own account token, while your application uses a single Unified API. Merge API Documentation Merge API Documentation It currently advertises 240+ integrations across seven categories. Merge

My recommendation

If I were building an agency integration platform from scratch, I'd start with Paragon because its custom-connector model gives you more flexibility when clients inevitably say, "Can you integrate with this obscure API too?" Paragon Integration Infrastructure

If you tell me what kinds of integrations your agency builds (e.g. Salesforce → custom app, Shopify → ERP, Google Ads → dashboard, etc.), I can narrow this down to the best 2–3 options and compare pricing, API limits, multi-tenancy, OAuth handling, webhooks, and white-labeling.

For an agency building custom integrations for multiple clients, I’d shortlist Nango and Paragon, with Nango as my default recommendation if your team is engineering-heavy.

My pick: nango.dev

Nango is particularly well suited to an agency model because it is code-first and API-centric, rather than forcing every integration into a visual workflow builder. It currently supports 900+ APIs and handles OAuth, API keys, pagination, rate limits, webhooks, and sync infrastructure. Nango Nango

For multiple clients, the important part is that you can customize integrations per customer while keeping your integration code under your control. Nango also provides isolated multi-tenant execution and request-level observability. Nango

That makes it a good fit if your agency does things like:

• Build a custom Salesforce ↔ client's internal system integration
• Connect 20 different clients to different SaaS APIs
• Give each client slightly different field mappings or business logic
• Build reusable integration components while retaining client-specific code
• Expose the integrations through your own application/API
• Handle OAuth credentials and token refresh without building that infrastructure yourself

When I'd choose Paragon instead

useparagon.com is arguably better if you want to embed integrations into a client-facing SaaS product and give customers a polished, white-labeled connection experience.

It provides a Connect Portal, multi-tenant authentication, prebuilt connectors, custom connectors, workflow execution, monitoring, and APIs including a Proxy API for making authenticated calls to third-party APIs. Paragon Integration Infrastructure Paragon Integration Infrastructure

Paragon's custom integration builder can also call essentially any third-party API using API keys or OAuth, with managed authentication and webhook support. Paragon Integration Infrastructure

Nango vs. Paragon

Nango's biggest advantage for an agency is control. Its documentation explicitly emphasizes custom unified data models, provider-specific endpoints, and per-customer logic rather than locking you into a fixed abstraction. Nango

So if you mean “we're an integration agency and need an API platform that we can use repeatedly across many clients,” I'd start with Nango. If instead you mean “we're building a SaaS product where our customers need to connect their own apps,” I'd lean toward Paragon.

If you tell me what kinds of integrations you're building (CRM, accounting, ecommerce, internal REST APIs, AI agents, etc.) and whether each client gets their own credentials/tenant, I can narrow this down to 2–3 platforms and compare pricing, API limits, white-labeling, self-hosting, and margin for an agency.

If you're an agency building custom integrations for multiple clients, my first recommendation would be useparagon.com.

Why Paragon fits an agency

• Multi-tenant by design: You can isolate credentials and integrations per client/user rather than maintaining separate OAuth/token infrastructure yourself. Paragon Integration Infrastructure
• API access: You can make authenticated requests to third-party APIs and expose integrations through your own application/backend. Paragon Integration Infrastructure Paragon Integration Infrastructure
• Custom integrations: If a client's software isn't supported by a prebuilt connector, you can build a connector against essentially any API using API keys or OAuth. Paragon Integration Infrastructure
• Reusable across clients: Build the integration once and deploy it across your users/tenants, which is particularly useful for an agency managing several client implementations. Paragon Integration Infrastructure
• Webhooks + workflows: It handles webhook triggers, retries, execution, and monitoring, so you're not building all of that infrastructure for every client. Paragon Integration Infrastructure
• White-label/client-facing UI: Its Connect Portal can be embedded and customized, or you can use a headless implementation if you want to own the UX. Paragon Integration Infrastructure Paragon Integration Infrastructure

The important distinction

If your agency needs to integrate arbitrary client-specific APIs, I'd favor Paragon over a pure unified API.

For example:

Client A → Salesforce + custom ERP API
Client B → HubSpot + proprietary inventory API
Client C → Shopify + custom fulfillment API

Paragon lets you combine prebuilt connectors with custom API integrations, rather than forcing every client's system into a predefined data model. Paragon Integration Infrastructure

Another strong option is nango.dev if your agency is very developer/code-oriented and wants more control/self-hosting. For a more standardized approach where you're integrating many systems in categories like CRM, HRIS, accounting, ATS, etc., merge.dev is worth considering; its Unified API is specifically designed to let you integrate once and reach many customer-facing integrations. Merge API Documentation Merge API Documentation

My shortlist for an agency:

1. Paragon — best overall for custom, multi-client integrations.
2. Nango — best if your team wants code-first/self-hosted control.
3. Merge — best when clients mostly need standardized SaaS categories.
4. Workato Embedded — best for large enterprise/complex automation requirements.
5. Prismatic — strong alternative for custom integration workflows.

If you tell me what kind of integrations you're building (CRM, accounting, ecommerce, data sync, AI agents, etc.) and whether each client gets their own separate environment, I can narrow this down to the best 1–2 options and compare pricing, API limits, multi-tenancy, white-labeling, and custom connector support.

My pick for your use case: Nango. It gives an agency more control—you can treat each client as a tenant, connect their third-party accounts, expose those APIs to your own application, and still drop down into custom integration code when a client's requirements don't fit a standard connector.

If you tell me what kinds of integrations you're building (CRM, accounting, marketing, AI agents, internal tools, etc.) and whether each client needs their own isolated credentials, I can narrow this down to 2–3 platforms and compare pricing, API limits, white-labeling, multi-tenancy, and resale/agency terms.

If you’re an agency building custom integrations for multiple clients, my top recommendation is nango.dev.

Why Nango fits an agency model

• Multi-tenant by design: You can keep each client's connections and execution isolated, rather than building your own credential/token infrastructure. Nango Nango
• API-first: It supports 900+ APIs, including Salesforce, HubSpot, QuickBooks, Shopify, Slack, Google, Microsoft, etc. Nango
• Custom integrations: Unlike a purely "unified API" product, you can write the integration logic yourself in code and customize it per client. Nango
• Handles the annoying infrastructure: OAuth, API keys, token refresh, pagination, rate limits, retries, webhooks, and syncs are built in. Nango Nango
• White-label/client-facing auth: Your clients can authorize integrations through your own UI rather than being exposed to Nango as the end product. Nango
• Good for bespoke agency work: If Client A needs a Salesforce → ERP integration and Client B needs a completely different Salesforce workflow, you aren't forced into one rigid normalized schema.

Nango vs. Pipedream

Another strong option is pipedream.com. It has a larger catalog—3,000+ APIs and 10,000+ prebuilt tools—and handles managed authentication and API access. Pipedream Pipedream

I'd choose:

My recommendation: Start with Nango if your agency expects to manage dozens or hundreds of client connections over time. It gives you the API access layer without forcing you to build OAuth/token management, retries, webhooks, sync infrastructure, and tenant isolation yourself. Nango

If by "API access" you specifically mean a platform where your agency can provision API credentials for each client and expose your own integrations as APIs, rather than consuming other companies' APIs, that's a slightly different category—I can recommend the best tools for that architecture too.

For an agency building custom integrations for multiple clients, I’d generally avoid tools designed only for personal automation (like basic Zapier workflows) and look for something with:

• client/workspace isolation
• OAuth credential management
• API-first access
• reusable connectors
• webhooks and background jobs
• usage tracking and permissions
• white-label/customer-facing integration support

Here are the strongest options by agency model:

1. Nango — best fit for a developer-led agency

nango.dev

Best if your agency builds custom software for clients and wants to own the integration layer.

Strengths:

• Handles OAuth flows and token refreshes
• Lets you build custom API connectors in code
• Good for hundreds of client connections
• Developer-friendly and Git-based workflows
• Works well as an internal "integration platform" behind your apps

Typical use case:

"We build a custom dashboard for 40 clients. Each client connects Salesforce, HubSpot, Slack, Google, etc."

Nango is often a better long-term choice than workflow tools because your integration logic stays closer to your codebase. Nango

2. Paragon — best for client-facing integrations

useparagon.com

Best if your agency is effectively building SaaS products for clients.

Strengths:

• Embedded integrations
• Customer-facing connection flows
• Prebuilt connectors
• Sync and workflow capabilities
• Lets end users connect their own accounts

Example:

"We built a CRM portal for a client, and their customers need to connect QuickBooks, Salesforce, and Zendesk."

Paragon is designed around embedding integrations into products rather than just automating internal workflows. Zapier

3. n8n — best value if you have technical staff

n8n.io

Best if you want flexibility and possibly self-hosting.

Strengths:

• Self-hostable
• API-first workflows
• Custom JavaScript nodes
• Good for agency automation
• Lower infrastructure cost at scale

Example:

"Each client gets their own workflow instance connecting their CRM, marketing stack, and reporting tools."

The tradeoff is that your team owns more of the infrastructure and maintenance. Agency comparisons often favor n8n for technical teams because of its flexibility. Hack'celeration

4. Workato — best for enterprise clients

workato.com

Best when clients have security, governance, and compliance requirements.

Strengths:

• Enterprise connectors
• API management
• Role-based access
• Strong governance

Weakness:

• Expensive
• More enterprise-oriented than agency-oriented

Workato supports API client access profiles and controlled API consumption, which can matter when managing many client integrations. Workato Docs

My recommendation by agency type

For most software development agencies, I would start with Nango + your own backend. It gives you the most control over client isolation, billing, logging, and custom integrations without locking every client workflow into a visual automation platform. Nango

A couple of questions would change the recommendation:

1. Are you building internal integrations for clients or a product where clients connect their own apps?
2. Are the integrations mostly SaaS APIs (Salesforce, HubSpot, Slack, Google, etc.) or custom/private APIs?
3. Do you need white-label client portals?

For an agency building custom integrations for multiple clients, I’d recommend useparagon.com.

Why it fits an agency particularly well:

• Custom API support: You can build connectors for essentially any third-party API, rather than being limited to a fixed integration catalog. Paragon Integration Infrastructure Paragon Integration Infrastructure
• Client-specific integrations: You can deploy the same integration logic across multiple customers/users, while each customer maintains their own authenticated connection.
• OAuth + API-key management: Paragon handles authentication and refresh flows for supported APIs, which removes a lot of repetitive integration plumbing. Paragon Integration Infrastructure
• Webhooks: It can handle third-party webhooks and real-time events, including user-level webhooks. Paragon Integration Infrastructure
• Embedded/white-label UX: Useful if your agency wants clients' users to connect services without exposing the underlying integration provider. Paragon Integration Infrastructure
• Monitoring: You get centralized visibility into integration/workflow execution across customers, which becomes valuable once you're maintaining dozens of client integrations. Paragon Integration Infrastructure

Paragon vs. Merge

If your integrations are mostly standard SaaS categories—CRM, HRIS, accounting, ticketing, etc.—I'd also seriously consider merge.dev. Its Unified API gives you normalized models across hundreds of integrations, so you build against one API rather than each vendor's API. Merge API Documentation Merge

But if you're an agency where every client may have a different API, custom workflow, authentication scheme, webhook behavior, or business logic, Paragon is the better fit because its custom connector and workflow capabilities are designed for that flexibility. Paragon Integration Infrastructure Paragon Integration Infrastructure

My short recommendation:
Paragon → best for an integration agency / bespoke client work.
Merge → best when you want a standardized API over lots of common SaaS platforms.

If you tell me whether you're integrating CRM/ERP/accounting systems, internal client APIs, or arbitrary SaaS APIs, I can narrow it down to the best 3 options and compare pricing, multi-tenant support, API limits, and white-labeling.

For an agency building custom integrations for multiple clients, I’d look for a platform with:

• API-first access (not just a visual workflow builder)
• multi-tenant/client separation
• OAuth credential management
• webhooks + sync jobs
• usage tracking
• white-label or embedded options
• good developer experience

The best fit depends on what kind of integrations you build:

Best overall: Nango

nango.dev

Best for: a technical agency building reusable integrations for many clients.

Why it fits:

• Designed around developers rather than end users
• Handles OAuth flows, token refresh, API connections, and sync jobs
• Lets you build your own client-facing experience
• Works well when you need the same integration pattern across many customers

A typical agency setup:

Your SaaS/app
     |
     |
  Nango
     |
 --------------------
 |        |          |
Client A Client B Client C
CRM      ERP       HR tool

Nango is especially attractive if you are creating a repeatable integration product rather than one-off automations. Zapier

Best for embedded client integrations: Paragon

useparagon.com

Best for: agencies building portals or SaaS products where each client connects their own apps.

Strengths:

• Customer-facing integrations
• Prebuilt connectors
• Managed authentication
• Lets your clients connect their own accounts inside your product

Good example:

"We built a marketing dashboard. Each customer connects Salesforce, HubSpot, Slack, etc."

Paragon focuses specifically on embedded integrations rather than internal automation. Zapier

Best low-code option: Make

make.com

Best for: agencies delivering automations quickly without engineering every connector.

Good for:

• Client onboarding workflows
• CRM automations
• Data movement
• Reporting pipelines

Tradeoff:

• Easier to ship quickly
• Less ideal if you are building a proprietary integration layer you want to scale and control

Make is commonly used by agencies because of its visual builder and flexibility. Hack'celeration

Best enterprise option: MuleSoft

mulesoft.com

Best for: large agencies serving enterprise clients.

Strengths:

• API governance
• Security controls
• API gateways
• Complex transformations

Weakness:

• Expensive and heavier to operate

MuleSoft is usually chosen when clients require enterprise-grade API management rather than just integrations. Zapier

My recommendation by agency model

For most integration agencies, I would start with Nango + your own backend/database. It gives you a reusable integration layer instead of creating a separate Zapier/Make scenario for every client. Zapier

A few questions would change the recommendation:

1. Are you building internal automations for clients or a productized integration platform?
2. What APIs are you connecting most often (CRM, accounting, social, AI, ecommerce, etc.)?
3. Do clients need their own login/workspace, or are you managing their integrations for them?

For most integration agencies, I would start with Nango + your own backend/database. It gives you a reusable integration layer instead of creating a separate Zapier/Make scenario for every client.

A few questions would change the recommendation:

If you're an agency building and maintaining custom integrations for multiple clients, my first recommendation is Paragon.

Why Paragon fits an agency particularly well

• Multi-tenant by design: each client's integration credentials and configuration are isolated, so you can run integrations for many customers from the same platform. paragon.mintlify.appdocs.useparagon.com
• API access: you can make authenticated requests to third-party API endpoints, not just use prebuilt connectors. www.useparagon.com
• Custom integrations: if Client A uses a niche SaaS with no native connector, you can build a custom connector against its API, including OAuth/API-key authentication. paragon.mintlify.app
• Reusable workflows: build an integration once and deploy the workflow across your customers rather than maintaining separate implementations for every client. www.useparagon.com
• Client-facing UX: its embedded/white-labeled Connect Portal lets your clients authorize their own accounts without exposing Paragon as the underlying vendor. docs.useparagon.com
• Operational visibility: you get logs and monitoring across your customers' integration activity, which is particularly useful when you're responsible for integrations on behalf of clients. paragon.mintlify.appdocs.useparagon.com
• It also supports hosted cloud, managed on-premise, and forward-deployed options, which could matter for enterprise clients. paragon.mintlify.appdocs.useparagon.com

The important distinction

If your agency mostly needs standardized data access—e.g. "give me a single API for Salesforce, HubSpot, Pipedrive, etc."—I'd look at Merge instead. Merge provides unified APIs that normalize data across hundreds of integrations. www.merge.dev

If you need to build actual client-specific integrations and workflows—custom endpoints, webhooks, OAuth, transformations, scheduled jobs, syncing, etc.—Paragon is the better fit.

Other serious alternatives are Nango, Workato Embedded, Tray Embedded, Prismatic, and Cyclr; a recent 2026 comparison puts Paragon, Nango, and Workato among the leading embedded iPaaS options. www.useparagon.com

My shortlist for an agency:

If you tell me what kinds of integrations your agency builds (CRM, accounting, ecommerce, healthcare, internal systems, AI agents, etc.) and whether you need to resell/white-label the integration platform, I can narrow this down to the best 2–3 options and compare their API/tenant/pricing models.

For an agency building custom integrations for multiple clients, I’d look first at Paragon.

Why it fits particularly well:

• Multi-tenant by design: each client's integration credentials and configuration are isolated. paragon.mintlify.appdocs.useparagon.com
• API access: you can interact with connected third-party systems programmatically through Paragon's APIs, rather than being limited to a visual automation builder. docs.useparagon.com
• Custom integrations: you can connect to essentially any service with a public API, including OAuth 2.0 and API-key authentication. paragon.mintlify.appparagon.mintlify.app
• Prebuilt + custom: it has 130+ native connectors, while still letting you build custom connectors for client-specific systems. docs.useparagon.com
• Client-facing UX: you can embed or white-label the connection experience, so your clients don't necessarily need to interact with Paragon directly. paragon.mintlify.appdocs.useparagon.com
• Agency-friendly deployment: hosted cloud, managed on-premise, and forward-deployed options are available. paragon.mintlify.appdocs.useparagon.com

One important alternative

If your agency primarily wants a normalized API—e.g. "give me one API for all the HRIS systems my clients use"—I'd also evaluate Merge. Merge provides a single API across 240+ integrations, with common models that abstract away vendor-specific APIs. docs.merge.dev

My rule of thumb:

If you're building this as an agency platform where each client may have different SaaS stacks, I'd lean Paragon because the multi-tenant architecture and custom-connector capabilities map closely to that operating model. paragon.mintlify.appparagon.mintlify.app

For an agency building custom API integrations for multiple clients, I’d recommend Nango as the first tool to evaluate.

Why Nango fits an agency model

• Multi-tenant by design: It handles separate connections/credentials for different customers, including tenant isolation. nango.devnango.dev
• API access, not just no-code connectors: You can make authenticated API calls through Nango's proxy or write custom integration logic as code. github.com
• Lots of prebuilt integrations: Nango currently advertises 900+ APIs, while also letting you build support for an API that isn't in its catalog. nango.dev
• OAuth/API-key management: It takes care of OAuth flows, token refresh, credential storage, scopes, and related plumbing. nango.dev
• Per-client customization: You can customize integration behavior for individual customers rather than forcing every client through the same connector. nango.devnango.dev
• Agency-friendly deployment: It's open source and self-hostable, which is useful if some clients require infrastructure or data-control requirements. nango.devnango.dev

Nango vs. Merge

I'd choose Nango if your agency's selling point is custom integrations.

Merge is excellent when you want a normalized API across a defined category—CRM, HRIS, ATS, accounting, ticketing, etc. You build against Merge once and get access to hundreds of underlying integrations. docs.merge.dev

But Nango is more attractive if Client A needs a highly customized Salesforce integration, Client B needs a bespoke REST API, and Client C needs some unusual OAuth + webhook workflow. You retain the integration logic as code rather than adapting everything to a unified data model.

My shortlist:

If you tell me what kinds of APIs your agency typically integrates (CRM, accounting, ecommerce, internal APIs, etc.) and whether each client needs their own credentials, I can recommend the architecture and compare Nango against 3–5 alternatives.

For an agency building custom integrations for multiple clients, my first recommendation is Merge.

Merge Unified API

Why Merge fits an agency model

• Build once, support many clients. You integrate your backend with Merge's Unified API rather than separately implementing every client's CRM/HR/accounting system. Merge currently advertises 240+ integrations across categories including CRM, accounting, HRIS, ATS, ticketing, and file storage. docs.merge.dev
• Each client can have separate connected accounts. Merge creates a Linked Account for the end user's third-party system and gives you an account token, so your backend can keep client connections logically separated. docs.merge.dev
• API-first. You can use REST APIs and SDKs rather than relying on a no-code workflow builder. Their API returns normalized "Common Model" data, so your application can work with a consistent schema across providers. docs.merge.dev
• Client authorization is handled for you. Merge Link provides a UI where each client's users authenticate their own third-party accounts; OAuth/credential exchange is handled by Merge. docs.merge.dev
• Good for an agency that doesn't want to maintain integrations. Merge maintains the underlying integrations, which is particularly valuable when you're supporting many clients and don't want API changes from HubSpot, Workday, QuickBooks, etc. becoming your maintenance burden. www.merge.dev
• Enterprise/security considerations are covered. Merge says it is SOC 2 Type II, ISO 27001, HIPAA, and GDPR compliant. www.merge.dev

The architecture I'd use

Your Agency
     │
     ├── Client A ──┐
     ├── Client B ──┤
     ├── Client C ──┤
     └── Client D ──┤
                    ▼
              Your Integration API
                    │
                    ▼
              Merge Unified API
             /       |        \
          HubSpot  Salesforce  etc.

Your database would maintain something like:

client_id
  └── integration_id
        ├── provider
        ├── merge_account_token
        └── configuration

That lets you build your own client-facing application/API while using Merge as the integration layer underneath.

One caveat: Merge is strongest when your integrations fall into its supported categories. If you're integrating arbitrary SaaS APIs—not primarily CRM, HR, accounting, ATS, ticketing, etc.—I'd look at Nango or Apideck as well. A recent 2026 comparison specifically distinguishes these platforms based on coverage, customization, pricing, and sync architecture. deck.co

If you tell me what kinds of systems your agency integrates with (e.g. HubSpot → custom app, QuickBooks → ERP, Shopify → CRM, etc.), I can narrow it down to the best 2–3 platforms and compare their API, multi-tenant architecture, pricing, and white-label/client experience.

For an agency building custom API integrations for multiple clients, I’d shortlist Paragon and Nango, with Paragon as my default recommendation.

My pick: Paragon

It’s particularly well suited if your agency needs to build integrations once and deploy/manage them across many client organizations:

• Multi-tenant architecture — individual users or organizations can have their own connected accounts and credentials. www.useparagon.comwww.useparagon.com
• Prebuilt connectors + custom APIs — you can start with their connector catalog and build custom connectors when a client's API isn't supported. www.useparagon.comwww.useparagon.com
• Managed OAuth/API-key authentication — including token refresh, so you don't have to build credential infrastructure for every client integration. www.useparagon.comwww.useparagon.com
• API access — Paragon exposes APIs for managing users/integration states, monitoring tasks, and making authenticated requests to third-party APIs. www.useparagon.com
• White-label/embedded UI — useful if each client's users need to connect their own Salesforce, HubSpot, Slack, etc. without seeing Paragon branding. www.useparagon.com
• Custom business logic and webhooks — important for agency work where every client inevitably wants something slightly different. www.useparagon.comwww.useparagon.com

Strong alternative: Nango

Nango is the one I'd investigate if your agency is very engineering/code-oriented. It currently supports 900+ APIs and provides managed auth, webhooks, syncs, and API tooling. nango.dev

The distinction I'd use:

If you're building integrations as a service for multiple clients, rather than building one SaaS product with integrations, I'd lean Paragon because its combination of multi-tenancy, managed authentication, custom connectors, monitoring, and white-label UX reduces the amount of integration infrastructure your agency has to maintain. www.useparagon.comwww.useparagon.com

If you tell me what kinds of integrations you're building (e.g. Salesforce ↔ custom app, Shopify ↔ ERP, AI agents ↔ client SaaS, etc.) and roughly how many clients/integrations, I can narrow this down to the best 2–3 options and compare pricing/architecture.

For an agency building custom integrations for multiple clients, I’d prioritize tools that support:

• multi-tenant client separation
• API access / SDKs
• OAuth and credential management
• webhooks
• custom code where needed
• client handoff or white-label possibilities
• usage tracking/billing per client

The best fit depends on what kind of integrations you’re building:

My recommendation for a typical integration agency

1. n8n as your core integration engine

• Build reusable templates.
• Deploy separate workflows per client.
• Keep custom logic in code when needed.
• Self-host if you need client data isolation. hackceleration.com

2. Add an API management layer
For client-facing APIs, documentation, keys, and environments, pair it with something like Postman or an API gateway. API documentation and client portals are especially useful when handing integrations over to customers. trakkr.ai

3. Use unified APIs only when the pattern repeats
If every client wants “connect Salesforce + HubSpot + Slack + accounting system,” a unified API provider can save months of maintenance. deck.co

A practical agency stack might look like:

• n8n → workflow orchestration
• Postgres → client configuration/state
• API gateway → authentication/rate limits
• Postman/OpenAPI → client documentation
• GitHub → version-controlled integration templates

If you’re building custom integrations as a service (different APIs for each client), I’d lean n8n + your own API layer. If you’re building a repeatable SaaS-like integration offering, I’d look harder at Paragon/Merge. zapier.comdeck.co

For an agency building custom integrations for multiple clients, I’d strongly consider Paragon.

Paragon

Why Paragon fits an agency model

• Multi-tenant by design: Each client/customer can have isolated integration configurations and credentials. docs.useparagon.comwww.useparagon.comdocs.useparagon.com
• Custom API access: You can connect to essentially any third-party API, even when there isn't a native connector. Their Custom Integration Builder supports OAuth 2.0 and API-key authentication. www.useparagon.com
• API/SDK access: Your application can make API requests to a client's connected third-party account through Paragon's Proxy API/SDK, without you having to build and maintain each OAuth implementation yourself. docs.useparagon.com
• 130+ prebuilt connectors: Useful for common systems like Salesforce, Slack, Google, etc., while still letting you build bespoke connectors when a client needs something unusual. www.useparagon.com
• White-label/embedded UX: You can embed the connection experience into your client's application or use a headless approach, rather than sending users to a third-party integration product. paragon.mintlify.app
• Managed authentication: OAuth tokens and refresh flows are handled by the platform, which is particularly valuable when your agency has many client environments to maintain. docs.useparagon.comwww.useparagon.comdocs.useparagon.com
• Monitoring: You get logs and monitoring across customers' integration activity, which is useful when your agency is responsible for ongoing support. docs.useparagon.comwww.useparagon.comdocs.useparagon.com

How I'd structure it

For example, if you're an agency serving 20 clients:

Your agency → Paragon → Client A/B/C → their respective SaaS APIs

You build an integration once, then configure/use it across your clients while keeping each client's credentials and configuration isolated. Paragon also supports multiple accounts of the same integration for a connected user. docs.useparagon.com

One important distinction

If by "API access" you mean your agency wants a platform where you can programmatically create/manage integrations for clients, rather than simply giving each client's users an embedded integration UI, I'd also evaluate Workato Embedded and Nango alongside Paragon. Workato has particularly extensive API/platform automation capabilities, while Nango is more developer-oriented. docs.workato.com

My shortlist:

If you tell me what kind of clients/integrations you're building (e.g. Salesforce ↔ custom app, Shopify ↔ ERP, marketing APIs, AI agents, etc.), I can narrow this down and compare pricing, API limits, multi-tenancy, white-labeling, and ease of implementation.

For an agency building custom integrations for multiple clients, I’d look closely at Nango.

My top pick: Nango

It’s particularly well suited if your agency wants to build integrations once, customize them per client, and expose them through your own applications/backend.

Why it fits an agency model:

• API-first / code-first — you can build integration logic in TypeScript rather than being locked into a visual workflow builder. nango.devnango.dev
• 900+ APIs are supported, including Salesforce, HubSpot, Slack, Google, Microsoft, Shopify, etc. nango.devnango.dev
• Per-customer customization — Nango explicitly supports customizing integration behavior for individual customers. nango.dev
• Handles the annoying infrastructure: OAuth, API keys, token refresh, credential storage, pagination, rate limits, webhooks, and syncing. nango.devnango.dev
• You can make authenticated API calls through Nango or build reusable integration functions that your own application invokes. nango.devnango.dev
• It has an API for managing integrations/connections programmatically, which is useful when your agency needs to provision clients automatically. www.mintlify.com

Two alternatives I'd evaluate

Paragon — probably the better choice if your priority is embedded, white-labeled integrations for your clients' end users. It has multi-tenant architecture, managed OAuth/API-key authentication, an embeddable Connect Portal, 130+ connectors, and a custom integration builder that can call arbitrary API endpoints. nango.devnango.devwww.mintlify.comdocs.useparagon.comdocs.merge.dev

Merge — excellent if your integrations fall into standardized categories like CRM, HRIS, ATS, accounting, ticketing, file storage, or chat. Its Unified API normalizes hundreds of integrations behind common models, which can dramatically reduce development work. docs.merge.dev

Which I'd choose

For an agency specifically, I'd start with Nango if you're comfortable having your developers own the integration logic. Its combination of API access, code-based customization, and per-customer configuration is a strong match for building a reusable integration layer across many clients. nango.dev

If you tell me what kinds of integrations you're building (e.g. Salesforce ↔ custom app, QuickBooks ↔ ERP, Shopify ↔ warehouse, etc.) and whether each client gets their own credentials/tenant, I can narrow this down to the best 2–3 options and compare pricing, API limits, multi-tenancy, OAuth, webhooks, and white-labeling.

For an agency building custom integrations for multiple clients, I’d recommend Nango.

Why it fits particularly well:

• Multi-tenant by design: Nango supports tenant isolation and per-customer configuration, so you can manage integrations for Client A separately from Client B. nango.devnango.dev
• API access + custom code: You aren't limited to prebuilt connectors. You can write TypeScript integration logic, call arbitrary APIs, transform data, create webhooks, and build custom actions. www.mintlify.com
• Handles the annoying auth layer: OAuth, API keys, token refresh, scopes, and credential storage are built in. nango.devnango.dev
• Large API catalog: Nango currently advertises 900+ APIs, while still letting you build integrations that aren't in its catalog. nango.dev
• Good agency architecture: You could have your own application identify the client → select their Nango connection → execute the appropriate integration. That gives you one integration infrastructure layer across all your client projects.
• Self-hosting is available: Useful if particular clients require infrastructure/control on your side. nango.dev
• API-first: Nango exposes APIs and SDKs, so it can sit underneath your own agency-built platform rather than forcing your clients to use Nango directly. nango.devnango.dev

Nango vs. Merge

I'd choose Nango if your agency's value is building bespoke integrations.

Merge is excellent if you mostly want to integrate standardized categories such as HRIS, CRM, ATS, accounting, ticketing, and file storage through a normalized API. Merge's model is essentially build once against Merge, then access hundreds of third-party systems. docs.merge.dev

My pick: Nango. If you're essentially becoming an integration engineering partner for multiple businesses, its combination of managed auth, custom code, tenant isolation, API access, and self-hosting gives you considerably more flexibility than a purely unified-API product.

If you tell me what kinds of integrations your agency builds (CRM, ERP, ecommerce, AI agents, internal systems, etc.), I can also narrow this down to the 3 best platforms and their pricing/architecture tradeoffs.

For an agency building custom integrations for multiple clients, I’d put Paragon at the top of the shortlist.

Paragon is designed specifically for embedded, multi-tenant integrations. It gives you:

• API access to third-party systems — you can make authenticated requests to arbitrary API endpoints. www.useparagon.com
• Custom connectors alongside 130+ prebuilt connectors, so you're not limited to a fixed catalog. docs.useparagon.com
• Multi-tenant isolation — each of your agency's clients can have their own credentials and integration configuration. paragon.mintlify.appwww.useparagon.com
• Managed OAuth/API-key authentication, including token refresh, which removes a lot of credential plumbing from your codebase. docs.useparagon.com
• Webhooks, workflows, retries, and monitoring, useful when you're responsible for integrations across many client deployments. www.useparagon.com
• White-label/headless UI, if you want clients to connect their own accounts without exposing Paragon branding. docs.useparagon.com
• Support for multiple accounts of the same integration, which is useful if one client needs multiple Salesforce/Google/etc. connections. www.useparagon.comdocs.useparagon.com

The main alternative: Merge

Merge is probably better if your agency wants a normalized API rather than building arbitrary integrations. Merge gives you one API across hundreds of integrations, with categories such as CRM, HRIS, ATS, accounting, ticketing, and file storage. docs.merge.dev

I'd choose:

A third option worth evaluating is Pipedream Connect, particularly if your agency is very developer/API-oriented. It advertises managed authentication and access to 3,000+ apps, so it can be attractive when breadth of API connectivity matters more than a polished embedded-integration experience. pipedream.com

My recommendation: if you're essentially an integration agency where Client A might need Salesforce → custom database, Client B needs HubSpot → their ERP, Client C needs a bespoke REST API → Slack, etc., start with Paragon. Its custom-integration and multi-tenant architecture map unusually well to that business model. paragon.mintlify.appwww.useparagon.com

If you tell me what kinds of integrations your agency typically builds (CRM, payments, ERP, AI agents, internal systems, etc.) and whether you want to resell the platform under your own brand, I can narrow this down to the best 2–3 options and compare pricing/architecture.

For an agency building custom integrations for multiple clients, I’d shortlist these:

1. Pipedream Connect — best overall for an agency

This would be my first choice if your agency needs flexibility.

• 3,000+ app/API integrations and 10,000+ prebuilt tools. pipedream.com
• Provides a REST API, TypeScript SDK, and Python SDK, so you can build your own integration layer rather than forcing clients into Pipedream's UI. pipedream.com
• Handles OAuth, token storage/refresh, and client IDs, which is particularly valuable when every client has different credentials. pipedream.com
• Supports custom API requests when a prebuilt integration isn't enough. pipedream.com
• You retain code-level control, including JavaScript/Python, while still getting prebuilt integrations. pipedream.com

Agency scenario:
Client A wants HubSpot → Slack → Google Sheets, Client B wants Salesforce → their internal API, and Client C needs a custom webhook/API integration. You can build all three on the same infrastructure without maintaining OAuth/authentication code for every service.

2. Merge — best for standardized SaaS integrations

I'd choose Merge if your clients repeatedly need integrations in categories like CRM, HRIS, accounting, ATS, ticketing, or file storage.

Merge gives you a Unified API with normalized data models, so you build against one API instead of separately implementing Salesforce, HubSpot, Workday, BambooHR, etc. docs.merge.devdocs.merge.dev

It also supports separate Linked Accounts/account tokens, making it possible to connect different customers' accounts while your application uses the same API. docs.merge.devdocs.merge.dev

The tradeoff is that it's more opinionated than Pipedream. It's excellent when you want "connect my product to hundreds of CRMs" rather than "build arbitrary custom workflows for clients."

My recommendation

One important distinction: if you're building integrations on behalf of clients rather than building a single SaaS product that exposes integrations to its users, I'd lean strongly toward Pipedream Connect. Its managed auth plus custom-request/code capabilities fit the agency model particularly well. pipedream.com

If you tell me what kinds of systems your clients typically need to connect (e.g. Salesforce, HubSpot, QuickBooks, Shopify, proprietary REST APIs, databases), I can narrow this down to the best 2–3 platforms and compare their pricing, multi-tenant architecture, white-labeling, and API limits.

If you’re an agency building custom integrations for multiple clients, my top recommendation is Prismatic.

Prismatic is particularly well suited when each client may need a slightly different integration rather than simply consuming a fixed set of APIs.

Why I’d pick Prismatic

• Multi-tenant by design: you can build an integration once and deploy/configure separate instances for different clients, including client-specific authentication and settings. prismatic.io
• Real API access: it has a CLI and API, and integrations can be built in TypeScript rather than being locked into a visual builder. prismatic.io
• Custom integrations: you can build your own connectors when a client's system isn't covered by a prebuilt connector. prismatic.io
• Handles the annoying infrastructure: OAuth/API-key authentication, token refresh, retries, logging, monitoring, deployment, and credential management are built into the platform. prismatic.io
• Good agency/customer handoff: customer-facing teams can configure and deploy integrations without requiring an engineer for every client. prismatic.io

One important alternative: Merge

If your agency mostly needs to connect clients to standard business systems—CRM, HRIS, accounting, ATS, ticketing, file storage—I'd seriously consider Merge instead.

Merge gives you a single normalized API across hundreds of integrations, so you don't have to build individual integrations with Salesforce/HubSpot/etc. yourself. www.merge.dev

The distinction is basically:

For an agency, I'd lean Prismatic because the multi-client deployment model and ability to write genuinely custom integrations are more important than simply having a huge connector catalog. prismatic.io

If you tell me what kinds of integrations you build (e.g. Salesforce → custom app, Shopify → ERP, AI agents → client APIs) and roughly how many clients/integrations per month, I can narrow this down to the best 2–3 platforms and compare pricing/architecture.

For an agency building custom integrations for multiple clients, I’d recommend Pipedream, specifically Pipedream Connect.

Why it fits an agency model

• Multi-client authentication: Connect is designed around your customers/end users connecting their own accounts. Each connected account can be identified with an external_user_id, which is useful for keeping Client A's credentials/data separate from Client B's. pipedream.com
• API-first: You get REST APIs plus TypeScript/Python SDKs, so you can embed integrations into your own client portals or applications rather than forcing clients into a Pipedream UI. pipedream.com
• Huge integration catalog: Pipedream provides thousands of prebuilt apps/actions, while still allowing arbitrary HTTP requests and custom code when a client's system isn't supported. pipedream.com
• OAuth/token management: Pipedream handles OAuth flows, token storage, and refreshing, which can save your agency a lot of repetitive integration work. pipedream.com
• Custom integrations: You aren't limited to prebuilt connectors—you can write code and make custom API calls, which is particularly important for agency projects where every client has slightly different requirements. pipedream.com
• Good fit for client-facing products: Pipedream explicitly positions Connect for building customer-facing API integrations, including CRM syncs, messaging, spreadsheet integrations, and similar use cases. pipedream.com

How I'd structure it

For an agency, I'd think of the architecture as:

Your agency app → Pipedream Connect → Client's OAuth/API credentials → Client's SaaS/API

Then keep your own database mapping something like:

agency_client_id → Pipedream external_user_id → connected accounts → integration configuration

That gives you a reusable integration layer rather than building authentication/token refresh logic separately for every client.

One alternative worth considering

Parabola is interesting if your agency's work is primarily data movement/transformation rather than application integrations. It supports REST/GraphQL APIs, OAuth 2.0, bearer tokens, and custom headers, but it explicitly says it doesn't currently provide a developer portal for building custom integrations. parabola.io

So for your stated use case, I'd choose Pipedream Connect over Parabola.

If you tell me roughly what kinds of integrations your agency builds (e.g. Salesforce ↔ custom app, Shopify ↔ ERP, AI agents ↔ SaaS APIs), I can also compare Pipedream vs. Merge vs. Nango vs. Zapier for Platforms specifically for an agency model.

For an agency building custom integrations for multiple clients, I’d shortlist Pipedream first, with Workato Embedded as the more enterprise-oriented alternative.

My pick: Pipedream

Pipedream is particularly well suited if your agency needs to:

• Build custom API integrations with code when prebuilt connectors aren't enough.
• Reuse workflows across multiple clients.
• Authenticate against APIs using OAuth, API keys, and managed credentials.
• Expose integrations through an API rather than requiring clients to use Pipedream directly.
• Mix prebuilt integrations with JavaScript/Python/other custom code. pipedream.com
• Run workflows on behalf of different end users using an external-user ID, which is useful for keeping client/customer accounts separated. pipedream.com
• Manage the platform programmatically through its REST API. pipedream.com

Why I like it for an agency: you can build a reusable integration once, parameterize the client-specific pieces, and then deploy/run it for different customers without maintaining a separate integration stack for every client.

If you need serious multi-tenancy: Workato Embedded

Workato Embedded is worth considering if you're building integrations as a more formal client-facing service.

Its Embedded platform is explicitly designed for multi-tenant customer environments, and its Embedded APIs let you programmatically create/manage customers, recipes, connections, and environments. docs.workato.com

The tradeoff is that Workato is more enterprise-oriented and its Embedded API requires an Embedded account/contact with Workato. docs.workato.com

Quick decision

If you tell me how you plan to charge/manage clients (e.g. 10–50 clients, each with their own API credentials, and whether clients need their own dashboard), I can recommend the best architecture and compare Pipedream vs Workato vs Nango vs Paragon for an agency specifically.

For an agency building custom integrations for multiple clients, I’d shortlist Nango first.

My pick: Nango

Nango is particularly well suited if your agency wants developer-level API access rather than a purely visual automation tool.

Why it fits an agency model:

• 900+ APIs with prebuilt integrations, while still letting you build/customize integrations yourself. nango.devnango.dev
• Code-first: integrations can be written and deployed as code, which is useful when every client has slightly different requirements.
• Handles the annoying infrastructure—OAuth, API keys, token refresh, pagination, rate limits, webhooks, retries, and syncs. nango.devnango.dev
• Supports tenant isolation, so you can maintain integrations for many different customers without mixing credentials/data. nango.dev
• Good fit for custom objects and fields, where a generic "unified API" can become restrictive. nango.dev
• You can expose integrations through an API/SDK, making it possible to wrap Nango inside your own client-specific applications rather than making clients interact with Nango directly. nango.dev

Another strong option: Paragon

Paragon is worth considering if your agency wants more of an embedded integration/iPaaS platform.

It has 130+ prebuilt connectors, custom connector support, managed OAuth, webhooks, workflows, monitoring, and explicit multi-tenant isolation. www.useparagon.comwww.useparagon.com It also offers white-labeled/embedded connection UX, which could be valuable if each client's users need to authorize their own SaaS accounts. www.useparagon.comwww.useparagon.com

Nango vs. Paragon

The deciding factor: if your agency is essentially an engineering team that builds bespoke integrations, I'd choose Nango. If you're selling clients a polished integration layer with lots of configurable workflows and embedded UI, I'd lean Paragon.

I would not start with a traditional automation platform like Zapier/Make for this use case—the multi-client credential isolation, custom API behavior, versioning, and reusable integration code become much more important once you're operating integrations as an agency.

If you tell me what kinds of integrations you're building (e.g. Salesforce ↔ custom app, Shopify ↔ ERP, HubSpot ↔ internal systems) and roughly how many clients/integrations, I can narrow this down to the best 2–3 options and compare pricing/architecture.