ChatGPT answers, unedited

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 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.

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.