ChatGPT answers, unedited

If A/B subject-line testing needs to be genuinely free, I’d start with mailerlite.com.

• MailerLite: A/B testing is included on the free plan. You can test subject lines, sender name, content, and sending time, and have it automatically choose a winner based on opens or clicks. MailerLite MailerLite
• Free-plan catch: the free tier has relatively small sending/list limits, so it’s best if you’re starting small. MailerLite's current pages show A/B testing as a free feature, though its published free-plan limits appear to have changed recently, so I'd verify the limits when signing up. MailerLite MailerLite
• Brevo: has proper A/B testing for subject lines and content, but its A/B testing is currently not on the free plan. Brevo Help
• If you only need basic performance tracking: Brevo's free tier can still be attractive because of its larger contact allowance, but you'd need to pay for the A/B-testing feature. Omnisend

My practical pick

Try MailerLite first if your main requirement is:

“I want to send an email, test Subject A vs. Subject B, see which gets more opens/clicks, and do it for $0.”

It is unusually good at that specific requirement. MailerLite

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 free options for your situation.

If your main requirement is free A/B testing of email subject lines, I’d start with MailerLite.

• MailerLite — best fit for your requirement. Its free plan includes A/B testing, including subject lines, and lets you test up to 5 versions of a single element. It can automatically send the winning version to the remainder of your audience. MailerLite MailerLite
• Sender — another option, and its free tier is quite generous on sending volume, but there’s an important catch: Sender's current pricing page says A/B testing is not included on the free plan; it starts with Standard. Sender
• Brevo — skip it if free A/B testing is essential. Brevo supports subject-line/content A/B tests, but its own documentation says A/B testing isn't included in the Free plan. Brevo Help Brevo Help

What I'd try

mailerlite.com

It's particularly suitable if you're sending newsletters or marketing emails and want to experiment with things like:

• Subject A vs. Subject B
• Different sender names
• Different email content
• Open rate vs. click performance
• Automatically selecting the better-performing version

One caveat: MailerLite's multivariate testing is paid, but straightforward A/B testing is free. MailerLite MailerLite

If you tell me roughly how many subscribers you have (e.g. 200, 2,000, 20,000), I can narrow this down to the best free option for your list size.

If your main requirement is free A/B testing for email subject lines, I’d start with MailerLite.

• MailerLite — best fit for your use case. Its free plan includes A/B testing, and you can test subject lines, sender names, and other campaign elements. It also reports opens and clicks and can automatically send the winning version to the rest of the audience. MailerLite MailerLite
• Brevo — another good option. It supports A/B testing of subject lines or email content, with the ability to select a winner based on open or click rate. Brevo Help
• Mailchimp — less attractive if free testing is the priority. Its current documentation says email A/B testing is on paid plans, although Mailchimp's pages currently show some conflicting free-plan information, so I wouldn't choose it specifically for free A/B testing. Mailchimp Mailchimp

My pick

Try MailerLite first. It gives you the simplest path to:

Subject A vs Subject B → send to sample → measure opens/clicks → automatically send winner

One important caveat: if your list is small, don't put too much weight on tiny differences. A/B testing becomes much more informative as the number of recipients per variation increases.

mailerlite.com

If you tell me roughly how many subscribers you have (e.g. 200, 2,000, 20,000), I can narrow this down based on the free-plan limits and how useful the A/B testing will actually be.

If your main goal is free email sending + A/B subject line testing + basic performance analytics, I’d start with one of these:

My pick:

1. Try MailerLite first if you want a straightforward newsletter tool.

• Test subject lines.
• Track opens/clicks.
• See which campaigns perform better.
• Easy enough that you’ll actually run experiments regularly. MailerLite
• Try Kit if you’re building a creator newsletter, personal brand, or paid newsletter.
• Try Mailchimp if you expect to move into more advanced marketing automation later, but I wouldn’t choose it purely for free A/B testing today. Mailchimp

A simple testing workflow:

• Send subject line A to ~10–20% of your list.
• Send subject line B to another ~10–20%.
• Pick the winner based on open rate (for subject lines) or click rate (for content).
• Use the winner for the rest of the list.

If you tell me your approximate list size (e.g., 200, 5k, 50k subscribers) and whether this is for a newsletter, SaaS, ecommerce, or cold outreach, I can narrow it down.

If your main requirement is free email sending + simple A/B testing of subject lines, I’d try Sender first.

My picks

• 🥇 Sender — best free option

• Free plan supports up to 2,500 subscribers and 15,000 emails/month.
• Its Experiments feature can test subject lines, content, and send times, then automatically send the winning version to the remaining audience. Sender
• Best fit if you want actual A/B testing without immediately paying.
• 🥈 Brevo — good alternative

• Supports A/B tests for subject lines or email content and can select a winner based on open or click rate. Brevo Help
• However, Brevo's current pricing documentation places A/B testing under the Standard plan, starting at $18/month, so I wouldn't choose it specifically for free A/B testing. Brevo Help
• 🥉 Mailchimp — good analytics, but not for free A/B testing

• It has excellent A/B testing for subject lines, sender name, content, and send time. Mailchimp
• But A/B testing isn't included in the Free plan; it's available on paid marketing plans. Mailchimp
• Its free Subject Line Helper is still useful if you only want pre-send subject-line feedback. Mailchimp

What I'd do

Start with Sender. If you're sending a newsletter or marketing emails and have a modest list, it gives you the most straightforward combination of free sending + real subject-line experiments.

One important distinction: if by "email" you mean cold outreach rather than newsletters/marketing emails, I'd recommend a different category of tool entirely.

If you mainly want free email sending + simple A/B subject-line testing, I’d shortlist these:

My recommendation by use case:

• Just starting a newsletter: try MailerLite.
• You care most about testing and learning: try Sender or Mailercloud.
• You run an online store: consider Klaviyo (especially if you use Shopify), though the free limits are smaller. Biztoolkit
• You already have Gmail/Google Workspace and only need subject-line experiments: a lightweight tool like Mailsoftly may be worth looking at. Mailsoftly

For most people, I’d start with MailerLite: create 2 subject lines, send the test to a sample, pick the winner, and keep a simple spreadsheet of what worked. The biggest mistake with A/B testing is testing too many things at once—change only the subject line first so you actually learn something. Constant Contact

If you tell me your approximate list size (e.g., under 500 / 1k / 10k+ subscribers) and whether this is for a newsletter, business marketing, or cold outreach, I can narrow it down.

If your main requirement is free A/B testing of email subject lines, I’d start with MailerLite.

My pick: MailerLite

• A/B testing is included on the free plan, including subject lines. MailerLite MailerLite
• You can test multiple campaign elements, including subject line, content, sender name, and send time. MailerLite
• It also gives you campaign reporting/comparative reporting, so you can see which version actually performed better. MailerLite
• The interface is relatively straightforward, which matters if you're primarily trying to learn what subject lines work rather than build a complicated marketing system.

mailerlite.com

One important alternative: Brevo

Brevo is worth considering if you have a larger contact list, because its free plan allows unlimited contacts, but A/B testing is not on the free tier; Brevo puts it on its Standard plan. Brevo Help Brevo

So I'd rank them:

1. MailerLite — best choice if free A/B testing is the priority.
2. Brevo — better if list size/CRM matters more than free A/B testing.
3. Mailchimp — worth considering if you specifically want its ecosystem, but I'd choose MailerLite for your stated requirement.

One caveat: A/B testing is only useful with enough recipients. If you're sending to 100–200 people, differences between subject lines can easily be noise. For a small list, I'd focus on clicks/replies rather than open rate.

If you tell me roughly how many people are on your list and how often you send, I can narrow this down to the best genuinely-free option for your situation.

If your main requirement is free email sending + A/B subject line testing (or at least basic performance testing), I’d start with one of these:

My picks:

1. Try MailerLite first

• Best fit if you want to quickly test subject lines, see open/click performance, and not get buried in marketing features. Humblytics
• Try Mailchimp if you want a more mature analytics dashboard

• Better if you expect to grow into segmentation, ecommerce integrations, or more complex campaigns. Mailchimp
• Try Brevo if you send lots of operational emails

• Good for newsletters + customer emails in one place, but check exactly which A/B features are included in the free tier before committing. Tajo

A simple testing workflow:

• Send subject line A to ~20–30% of your list
• Send subject line B to another ~20–30%
• Pick the winner based on click rate, not only open rate (opens are less reliable now because of privacy protections)
• Send the winner to the remaining audience

If you tell me your approximate list size (e.g., under 500, 500–5k, 5k+) and whether this is for a newsletter, ecommerce, or SaaS/customer emails, I can narrow it down.

If free is the hard requirement and you specifically want A/B subject-line testing, the options are surprisingly limited.

My pick: Mailchimp — but with a catch

mailchimp.com has good A/B testing: you can test subject lines, sender name, content, or send time, and it can automatically send the winner to the remaining audience. Mailchimp Mailchimp

However, A/B testing is not included on Mailchimp's permanent free plan. It's available on Essentials and above. Mailchimp

So I'd use Mailchimp if you're okay with using a free trial initially, then deciding whether the paid plan is worth it.

If you need truly $0 forever

brevo.com is worth considering for general email marketing, because its free plan is genuinely free and includes 300 emails/day plus basic reporting/analytics. Brevo Help Brevo Help

But A/B testing is not on Brevo's free plan; it's included starting with the Standard plan. Brevo Help Brevo Help

What I'd do

One important point: if your list is small (e.g. <1,000 people), sophisticated A/B testing can be noisy. A simple approach of sending Subject A to half and Subject B to half, then comparing click rate (and open rate as a secondary metric) can work perfectly well.

If you tell me roughly how many subscribers you have (100 / 500 / 1,000 / 5,000+), I can recommend the best genuinely free option for your list size.

If your main requirement is free A/B testing of email subject lines, I’d start with mailerlite.com.

My shortlist

• 🥇 MailerLite — best fit

• A/B testing is included on the free plan.
• You can test subject lines and compare performance.
• It also provides comparative reporting, so you can see which version actually performed better. MailerLite MailerLite
• The current free plan lists 2,500 emails/month and 3 visual automations. MailerLite
• mailerlite.com
• 🥈 Brevo — good if your list is larger

• Free plan allows up to 100,000 contacts and 300 emails/day. Brevo Help
• However, A/B campaign testing isn't included on the free plan, so I'd rule it out if A/B testing is non-negotiable. Brevo Help
• brevo.com

What I'd choose

If you're trying to answer questions like:

"Does Subject A get more opens/clicks than Subject B?"

MailerLite is the one I'd try first. It lets you do that without paying, and you can later expand into testing other campaign variables. MailerLite

One caveat: if your list is very small, A/B results can be noisy. For meaningful testing, click rate is generally more useful than open rate, because modern email privacy features can make opens less reliable.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow this down to the best 2–3 free options for your situation.

If free is a hard requirement and you want actual A/B subject-line testing, I’d try Sender first.

My picks

• 🥇 Sender — best free option. Its free-forever plan supports up to 2,500 subscribers and 15,000 emails/month, and its Experiments feature can test subject lines, content, and send times, automatically selecting the better-performing version. Sender

sender.net

• 🥈 Brevo — good email platform, but not free for A/B testing. Brevo does support subject-line/content A/B tests, but its documentation explicitly says email A/B testing isn't included in the Free plan; it's in Standard, starting at $18/month. Brevo Help Brevo Help Brevo Help

brevo.com

• 🥉 Mailchimp — polished, but skip it if free testing is the goal. Mailchimp's A/B testing supports subject lines, sender name, content, and send time, but A/B testing requires Essentials or higher; the free plan doesn't include it. Mailchimp Mailchimp

mailchimp.com

Bottom line: I'd start with Sender. It's the closest match to “I want to send emails for free and actually experiment with what performs better.”

If you tell me roughly how many subscribers you have (e.g. 500, 2,000, 10,000), I can narrow it down further.

If your main requirement is free + subject-line A/B testing, I’d try MailerLite first.

• mailerlite.com — Best overall pick. Its free plan currently includes A/B testing, including subject lines, and you can test up to 5 versions of an individual element. It also gives you campaign reporting for opens and clicks. MailerLite MailerLite
• sender.net — Best if you want a larger free list. Sender advertises a free plan with up to 2,500 subscribers and 15,000 emails/month, with its Experiments feature able to test subject lines, content, and send times and automatically send the winner. Sender
• brevo.com — Good platform, but not my choice for your specific need. It supports proper A/B testing of subject lines/content, with winner selection based on opens or clicks, but its current pricing documentation puts A/B testing on the paid Standard tier rather than the free tier. Brevo Help Brevo Help

My recommendation

Start with MailerLite if you're under roughly 500 subscribers and want a simple newsletter tool where you can immediately experiment with:

Subject A vs. Subject B → send to a sample → automatically send the winner to everyone else.

That's much more useful than merely sending yourself test emails, because you're measuring actual subscriber behavior.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 1–2 free options for you.

If your main requirement is free A/B testing of email subject lines, I’d try MailerLite first.

• MailerLite — best overall free option. Its free plan includes A/B testing, up to 2,500 emails/month, and up to 250 subscribers. Its A/B testing can test subject lines and other campaign elements, and you can measure opens/clicks and select a winner. MailerLite MailerLite
• Mailchimp — good, but not if you need A/B testing for free. Mailchimp currently puts email A/B testing on Essentials and higher; its Free plan does not include A/B testing. Mailchimp Mailchimp
• Brevo — good for larger contact lists, with a free plan allowing up to 100,000 contacts and 300 emails/day, but its A/B testing is not the attractive free-tier option. Brevo Help

My pick

Start with MailerLite. It's probably the closest match to “I want to send newsletters for free and occasionally test Subject A vs Subject B.”

One caveat: with a small list, A/B results can be noisy. If you only have 100–300 subscribers, I'd treat the results as directional rather than statistically definitive.

mailerlite.com

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 free options for your specific volume.

If your main requirement is free + A/B testing of email subject lines, I’d start with mailerlite.com.

My pick: MailerLite

• Free plan: up to 250 subscribers and 2,500 emails/month. MailerLite MailerLite
• A/B testing is included on the free plan, including subject-line testing. MailerLite MailerLite
• It can automatically determine the better-performing version and send the winner to the remainder of your audience. MailerLite
• You get useful reporting for opens and clicks, so you can do straightforward performance testing without a complicated setup. MailerLite

One I'd skip for this specific need

brevo.com has A/B testing, including subject lines, but A/B testing isn't included in its free plan. The free tier is limited to 300 sends/day. Brevo Help Brevo Help

What I'd do

If you're testing things like:

A: “3 ways to save money this week”
B: “Are you wasting money on these 3 things?”

MailerLite is probably the simplest free starting point. You can test subject line A vs. B, let the platform measure the result, and use the winning version for the rest of the list.

If you tell me roughly how many subscribers you have (e.g. 100, 1,000, 10,000), I can give you the best 2–3 free options for your list size.

If free + subject-line A/B testing is the priority, I’d start with MailerLite.

My picks

1. MailerLite — best overall

• A/B testing is included on the free plan.
• You can test subject lines, and the platform can automatically select the winner based on engagement. MailerLite MailerLite
• Free plan currently includes 2,500 emails/month and 2 users, although the subscriber limit is currently listed as 250 on its pricing page. MailerLite
• Also has useful campaign reporting, so you can compare opens/clicks rather than just guessing.
• mailerlite.com
• Brevo — good if your list is bigger

• Free plan allows unlimited contacts and 300 email sends/day. Brevo Help
• However, A/B testing is not included in the free plan; it's on a paid tier. Brevo Help
• So I wouldn't choose it specifically for your requirement.

What I'd do

Try MailerLite first. It's unusually well suited to what you're asking for: you can send something like:

Subject A: 3 ways to save $100 this month
Subject B: Want to save $100 this month?

…and let the system test them against part of your audience and use the better performer for the remainder. MailerLite

One caveat: if your list is very small, A/B tests won't tell you much statistically. In that case, simple performance tracking across several campaigns can actually be more useful.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 genuinely free options.

If your main requirement is free email sending + A/B testing subject lines, I’d start with mailerlite.com.

My picks

1. MailerLite — best overall for your use case

• A/B testing is available on the free plan.
• You can test subject lines and determine the winner based on opens/clicks.
• It can automatically send the winning version to the remaining audience.
• Also gives you campaign reporting and automations. MailerLite MailerLite
• Best if: you're building a newsletter/list and want simple experimentation without paying.
• Brevo — good if you have a larger contact list

• Free plan allows unlimited contacts, but limits sending to 300 emails/day.
• Important catch: Brevo's A/B campaign testing is currently a paid feature, so it doesn't meet your "free A/B testing" requirement as well as MailerLite. Brevo Help Brevo Help
• Best if: contact-list size matters more than built-in A/B testing.
• Mailchimp — worth considering, but I'd put it behind MailerLite

• It's polished and has strong reporting, but A/B testing availability depends on the plan, so it's less attractive if $0 A/B testing is the deciding factor.

What I'd do

Try MailerLite first. It's unusually well suited to exactly what you're describing: create one email, make Subject A and Subject B, send each to a portion of your list, see which performs better, and use the winner.

One caveat: don't judge a subject-line test solely by open rate. Click rate is generally a more useful performance metric because modern privacy features can make opens less reliable.

If you tell me roughly how many people are on your list and how often you send, I can narrow this down to the best 2–3 genuinely free options for you.

If your priority is free + easy subject-line A/B testing, I’d start with MailerLite.

My shortlist

• MailerLite — best first choice. Its free tier is aimed at small lists, and current 2026 comparisons report subject-line/content A/B testing on the free plan. Biztoolkit
• Brevo — good alternative. It has a straightforward A/B testing workflow where you test two versions and can select the winner based on opens or clicks. However, Brevo's current documentation puts A/B testing under its paid Standard plan, so I wouldn't choose it specifically for free A/B testing without verifying what your account gets. Brevo Help Brevo Help
• Mailchimp — polished, but not my free pick. It has excellent A/B testing for subject lines, content, sender name, and send time, but its current documentation says A/B testing is on paid plans; the free account does have the Subject Line Helper, which is useful for evaluating subject lines before sending. Mailchimp Mailchimp

What I'd do

If you're sending a newsletter/marketing email to a relatively small list, try MailerLite first. You mainly want:

Subject A → 50% of test group
Subject B → 50% of test group
Winner → remainder of list

For meaningful testing, I'd focus more on click-through rate than open rate, because open-rate measurements can be noisy due to privacy protections and email-client behavior. AI Emaily

If you tell me roughly how many subscribers you have (e.g. 100, 1,000, 10,000) and whether this is a newsletter, business outreach, or ecommerce, I can narrow it down to the best genuinely-free option.

If your priority is free + actual A/B subject-line testing, I’d try MailerLite first.

My pick: mailerlite.com

• Free plan: up to 250 subscribers and 2,500 emails/month. MailerLite MailerLite
• A/B testing is included on the free plan, including testing subject lines. MailerLite MailerLite
• You can test different versions and measure opens/clicks, with the platform able to send the winning version to the remaining audience. MailerLite
• It also has useful campaign reporting, so you can do simple performance comparisons even when you're not running a formal A/B test.

One caveat: 250 subscribers is a fairly small free-plan limit as of June 2026. MailerLite

What about Brevo?

brevo.com is attractive because its free plan allows 100,000 stored contacts and 300 email sends/day, but A/B testing is not included in the free plan. Brevo Help Brevo Help

So for your specific requirement:

Bottom line: If you're starting with a relatively small list and want to experiment with subject lines, MailerLite is the obvious first one I'd try. MailerLite

If you tell me roughly how many subscribers you have (e.g. 100, 500, 5,000, 20,000), I can give you the best free/cheap option for that list size.

If your main requirement is free + A/B testing subject lines + basic performance reporting, I’d start with mailerlite.com.

My shortlist

• MailerLite — best fit. Its free plan includes A/B testing, and you can test subject lines and measure opens/clicks. It can also automatically select the winning version based on your chosen metric. MailerLite MailerLite
• Brevo — good alternative if you have a larger contact list. Its free tier allows unlimited contacts, but only 300 emails/day; importantly, its proper A/B campaign testing is not included on the free plan. Brevo Help
• Mailchimp — worth considering if you want a very mainstream platform, but I'd pick MailerLite specifically for your stated requirement.

What I'd do

Try MailerLite first. You can create something like:

Subject A: 3 ways to save $100 this month
Subject B: Want to save $100 this month?

Then send both to a portion of your audience and let the better-performing version go to the remainder. MailerLite says its A/B testing is available on the free plan. MailerLite

One caveat: free-plan limits appear to have changed recently, so I'd verify the current subscriber/email allowance when you sign up. MailerLite's current site lists 2,500 monthly emails and A/B testing on its free tier. MailerLite

Bottom line: MailerLite is the one I'd try first.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 free options for your situation.

If your main requirement is free + A/B testing of subject lines, I’d start with mailerlite.com.

My picks

• 🥇 MailerLite — best overall for you. Its free plan includes A/B testing, including subject lines, and you can test up to 5 versions of an element. It also gives you reporting so you can compare opens/clicks. MailerLite MailerLite
• 🥈 Brevo — good if you have a larger contact list. Its free tier allows 300 emails/day and unlimited contacts, but A/B campaign testing is not included on the free tier; you'd need a paid plan. Brevo Help Brevo
• Mailchimp — worth considering, but I wouldn't pick it specifically for this requirement because its free-tier A/B testing availability is more restrictive and has changed over time.

What I'd do

If you're sending a newsletter or marketing emails to a few hundred people, go with MailerLite. You can do something like:

A: 5 ways to save money this month
B: Are you wasting money on these 5 things?

Then send both to a portion of your list, see which performs better, and use the winner for the remaining recipients.

One important caveat: don't judge subject-line tests purely by opens if you can avoid it. Click rate or downstream conversions are generally more useful, since open tracking can be noisy.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can give you the best 2–3 free options for your specific situation.

If your main requirement is free email + subject line A/B testing (or at least easy performance testing), your choices are a bit limited because many platforms lock A/B testing behind paid plans. Here are the ones I’d consider:

Mailchimp is a strong testing platform: it supports testing subject lines, sender names, content, and send times, but its A/B testing features are tied to paid tiers rather than the free plan. Mailchimp Mailchimp

Brevo is attractive if you care more about sending volume, but its free tier does not include email A/B testing. Brevo Help Its paid plans add A/B testing for subject lines/content. Brevo Help

My recommendations

• If you absolutely need A/B subject testing without paying:

Try MailerLite first and verify the current free-tier feature set before building your workflow.

• If you can spend ~$10–20/month and want good testing tools:

Try Mailchimp or Brevo. They both have mature reporting and split-testing workflows. Brevo Help Mailchimp

• If you’re just trying to learn what subject lines work:

A workaround is to use any free email sender, split your list manually into two small groups, send subject A to one and subject B to the other, then compare:

• open rate
• click rate
• unsubscribe rate
• replies/conversions

For a small newsletter or creator list, I’d start with MailerLite. For a business trying to optimize campaigns seriously, I’d probably pay for Mailchimp/Brevo rather than fight free-tier limits.

If you need free email marketing with subject-line A/B testing or simple performance testing, I’d shortlist these:

My recommendation:

• If you have a small list (<1,000–2,000 subscribers): try MailerLite first. It’s simple, fast to learn, and you’re less likely to get buried in marketing-suite features.
• If you want a free tool mainly for sending volume: try Brevo. Its free plan is generous on contacts and daily sends, and it includes campaign analytics. Brevo Help
• If you want the most familiar “marketing platform” experience: try Mailchimp. It has mature reporting and A/B testing workflows, though some testing features are tied to paid tiers. Mailchimp Mailchimp

For simple subject testing, I’d avoid overcomplicating it:

1. Send Subject A to ~20–30% of your list.
2. Send Subject B to another ~20–30%.
3. Compare open rate (and click rate if the subject lines are close).
4. Use the winner for future campaigns.

If you tell me your approximate list size and whether this is for a newsletter, ecommerce, SaaS, or personal brand, I can narrow it to one choice.

If you want free email sending + actual A/B subject-line testing, I’d start with one of these:

1. MailerLite — best overall free pick

mailerlite.com

Why try it:

• Free plan includes A/B testing (including subject lines). MailerLite
• Very easy interface for newsletters, simple automations, landing pages, and signup forms.
• Good fit if you’re a solo creator, small business, newsletter operator, or early-stage startup.

Best if: you want something simple that you’ll actually use every week.

2. Mailchimp — best-known option, but check the free limits

mailchimp.com

Why try it:

• Strong reporting and mature analytics.
• Supports testing subject lines, content, sender names, and send times. Mailchimp

Watch out: A/B testing availability has moved between plans over time, so verify the current free-tier features before committing. Mailchimp

Best if: you expect to grow into a more advanced marketing stack.

3. Klaviyo — best for ecommerce

klaviyo.com

Why try it:

• Strong customer segmentation and revenue tracking.
• Good if your emails are tied to Shopify, products, or customer journeys.

Best if: you care about purchases more than newsletter opens.

4. Brevo — best if you send a lot of transactional email

brevo.com

Why try it:

• Generous free sending allowance.
• Good mix of marketing and transactional email features.

Watch out: A/B testing may require a paid tier depending on the feature. Biztoolkit

My recommendation:

• Newsletter / audience building: try MailerLite
• Ecommerce: try Klaviyo
• Professional marketing team: try Mailchimp
• High-volume sending: try Brevo

One thing to keep in mind: subject-line “A/B testing” is only useful if you have enough recipients. With a tiny list (e.g., under a few hundred people), results can bounce around too much; you’ll get better learning by testing across several sends rather than trusting a single winner.

If your main requirement is free + A/B subject-line testing, I’d start with mailerlite.com.

My pick: MailerLite

• Free plan: up to 250 subscribers and 2,500 emails/month. MailerLite
• A/B testing is included on the free plan, including email campaigns. MailerLite MailerLite
• You can test subject lines, sender name, content, and sending time. MailerLite
• It can automatically identify the better-performing version and send the winner to the remaining audience. MailerLite
• Reporting includes opens, clicks, and other campaign performance data. MailerLite

Another good option: Brevo

brevo.com has a free plan with 300 email sends/day and supports A/B tests for subject lines or email content. You can choose the winner based on open rate or click rate. Brevo Help Brevo Help

I'd choose:

• MailerLite → best if A/B testing is the priority and you have a small list.
• Brevo → better if you expect to have a larger contact database but don't send huge volumes every day.

One caveat: if by "performance testing" you mean testing different emails and measuring actual conversions/revenue, rather than just opens/clicks, the recommendation changes somewhat.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 free options.

If your main requirement is free + A/B testing of subject lines, I’d start with MailerLite.

My picks

Why MailerLite: its current documentation explicitly says A/B testing is available on all plans, including free, and you can test subject lines, content, sender name, etc. www.mailerlite.com

The basic workflow is exactly what you're describing: send subject-line A and B to a portion of your audience, measure performance, then use the better-performing version for the remainder. www.mailerlite.com

One caveat: MailerLite's free-plan limits have changed recently, and its current pricing page shows 250 subscribers / 2,500 monthly emails. www.mailerlite.com

I'd choose MailerLite if you're under ~250 subscribers. If you tell me roughly how many contacts you have and how many emails/month you send, I can narrow this down to the best 2–3 genuinely free options for your situation.

If free is a hard requirement and you specifically want A/B subject-line testing, the big catch is that the obvious choices don't currently give you both for free:

• Brevo — Free plan gives you 300 emails/day and basic reporting, but A/B testing is excluded. Their A/B testing supports subject lines and content, but you need a paid plan. help.brevo.comhelp.brevo.com
• Mailchimp — A/B testing, including subject lines, starts on Essentials, not the free plan. mailchimp.com

What I'd try

If you're willing to spend $0 initially, I'd actually start with Brevo for the sending/analytics and do simple manual testing:

1. Send subject A to ~50% of your list.
2. Send subject B to the other ~50%.
3. Compare open rate and click rate.
4. Use the result to inform your next campaign.

The downside is that Brevo won't automatically pick the winner and send it to the remaining audience on its free tier. help.brevo.comhelp.brevo.com

If your list is small (say <1,000 people) and you tell me roughly how many emails you send per month + whether this is newsletters, sales outreach, or transactional email, I can point you to a genuinely free setup that fits better.

If your priority is free + simple A/B testing of subject lines, I’d start with mailerlite.com.

• MailerLite — best overall free choice. Its free plan currently includes A/B testing, including subject-line testing, plus comparative reporting. The free tier allows up to 2,500 emails/month and 250 subscribers. MailerLite MailerLite
• Brevo — good alternative. It supports A/B tests for subject lines and email content, but its A/B testing is not on the free tier, so it doesn't fit your "free" requirement as well. Brevo Help
• Mailchimp — skip if A/B testing must remain free. Its email A/B testing requires the Essentials plan or higher. Mailchimp

My pick

Try MailerLite first. You can start with something as simple as:

Subject A: Your August update is here
Subject B: 3 things you shouldn't miss this August

Then have it determine which gets better opens/clicks and use the result to improve future campaigns.

mailerlite.com

If you tell me roughly how many people are on your list and whether you're sending a newsletter, sales emails, or cold outreach, I can narrow it down further.

If your main requirement is free + actual subject-line A/B testing, I’d try MailerLite first.

My picks

MailerLite explicitly includes campaign A/B testing on its $0 plan, and you can test subject lines and other campaign variables. It also gives you open/click reporting so you can judge performance. www.mailerlite.com

One important caveat: MailerLite changed its free tier in June 2026 to 250 active subscribers and 2,500 emails/month, so the free allowance is fairly small. www.mailerlite.com

Mailchimp is not my choice if “free A/B testing” is non-negotiable: its current documentation says A/B testing is available on paid plans, not the free plan. mailchimp.com

Brevo is also worth considering if you need more sending volume, but its current pricing puts A/B testing in the Standard tier rather than the free tier. help.brevo.com

Bottom line: Start with MailerLite. For a small newsletter/list, it gives you the cleanest combination of $0 cost + subject-line testing + performance reporting.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 options for your situation.

If your main requirement is free email + A/B testing of subject lines, I’d start with MailerLite.

My pick: MailerLite

Its current free plan includes:

• A/B testing — including subject lines
• Up to 250 subscribers
• 2,500 emails/month
• Campaign performance reporting
• Automations and signup forms
• No credit card required www.mailerlite.com

Their A/B testing can compare multiple versions of an element and can determine winners based on opens, clicks, or conversions. www.mailerlite.com

Try MailerLite free

What about the alternatives?

One caveat: MailerLite's free subscriber limit is only 250, so if you're already above that, the recommendation changes.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can give you the best 2–3 free options for your specific situation.

If your priority is free + A/B subject-line testing, I’d try MailerLite first.

My picks

MailerLite explicitly includes A/B testing on its free plan, and you can test different subject lines and determine winners based on opens/clicks. Its free plan also includes comparative reporting. www.mailerlite.com

Brevo is interesting because its free plan allows up to 100,000 stored contacts, but A/B testing is specifically excluded from the free plan; you need the Standard plan for it. help.brevo.com

So I'd start with MailerLite. It's unusually generous for this particular use case: you can actually run subject-line experiments without paying.

If by “simple performance testing” you mean “send Subject A to 20%, Subject B to 20%, then automatically send the winner to the remaining 60%,” MailerLite supports that kind of workflow. www.mailerlite.com

Start with MailerLite's free plan

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 free options.

If your main requirement is free + A/B testing of subject lines, I’d try MailerLite first.

My shortlist

Why MailerLite: its current free plan explicitly includes A/B testing and comparative reporting, with up to 2,500 emails/month and up to 250 subscribers. Its A/B testing can test subject lines and other campaign elements, and it can automatically send the winning version to the remainder of your list. www.mailerlite.com

Try MailerLite free

One caveat: if by "performance testing" you mean testing deliverability/inbox placement rather than testing which subject line gets more opens/clicks, that's a different requirement.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow this down to the best 2–3 free options for your situation.

If free + A/B subject-line testing is the priority, I’d try MailerLite first.

My shortlist

MailerLite is the standout because its free plan explicitly includes A/B testing, and you can test subject lines, sender name, email content, and sending time. It can also automatically send the winning version to the remainder of your list. www.mailerlite.com

Start with MailerLite's free plan

Kit is worth considering if you're primarily a newsletter/content creator. Its free tier supports A/B testing two subject lines, with the winner determined by open rate and then sent to the remaining audience. help.kit.com

Kit

I wouldn't choose Brevo specifically for this requirement: although Brevo supports A/B testing, its current documentation says email A/B testing isn't included in the Free plan. help.brevo.com

My recommendation

Try MailerLite. It's probably the closest match to "I just want a free email tool where I can send two subject lines and see which performs better."

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 1–2 options for your situation.

If free + actual A/B subject-line testing is the priority, I’d try Sender first.

Sender explicitly advertises A/B testing and a free-forever plan with 2,500 subscribers and 15,000 emails/month. www.sender.net

One important distinction: Sender's current documentation is a little inconsistent—its feature page says A/B testing can start on the free plan, while another current Sender page says A/B testing is on the Standard tier. www.sender.net So I'd verify the feature is actually available in the free account before moving your list over.

If you want the simplest possible setup: I'd test Sender first. You can run something like:

• A: “Your weekend plans just got better”
• B: “20% off ends Sunday”
• Send each to a portion of your list
• Compare opens/clicks
• Use the better-performing subject for the remainder

If by “performance testing” you mean testing subject lines automatically and having the winner sent to everyone else, tell me roughly how many subscribers you have and how often you send, and I can narrow this down to the best 2–3 genuinely free options.

If A/B subject-line testing on a genuinely free plan is the main requirement, I’d try MailerLite first.

My picks

MailerLite: Its free plan explicitly includes A/B testing, comparative reporting, and up to 2,500 emails/month. Its A/B testing can test subject lines and determine a winner based on opens, clicks, or conversions. www.mailerlite.com

Try MailerLite

Brevo: The free plan is quite generous for sending—300 emails/day—but A/B testing is excluded from Free and starts on the Standard plan. help.brevo.com

Try Brevo

Mailchimp: Its subject-line helper is free, but actual A/B testing is currently included with paid marketing plans, so I wouldn't choose it if "free A/B testing" is non-negotiable. mailchimp.com

Try Mailchimp

Bottom line: Start with MailerLite. It gives you the simplest combination of free sending + subject-line A/B tests + useful performance data without immediately requiring a paid upgrade.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can also narrow it down to the best 2–3 options for your specific volume.

If free + A/B subject-line testing is the priority, I’d start with MailerLite.

My picks

Why MailerLite: its current free plan explicitly includes A/B testing, with up to 2,500 emails/month. You can test subject lines and other campaign elements, and see opens/clicks in the reporting. www.mailerlite.comwww.brevo.com

One particularly useful feature is that MailerLite lets you test subject line, sender, content, or sending time. www.mailerlite.com

Brevo is worth considering if you have a large list but don't email very frequently: its free tier allows 300 emails/day, but its A/B testing is currently listed under the paid Standard plan. www.brevo.com

My recommendation: try MailerLite first. If your main goal is simply “send newsletters for free and test Subject A vs Subject B to see which gets more opens”, it fits almost exactly.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best 2–3 free options for your specific volume.

If your main requirement is free + subject-line A/B testing, I’d try MailerLite first.

My picks

Why MailerLite: its free plan explicitly includes campaign A/B testing, and you can test subject lines, sender, content, and sending time. It can automatically determine the winner based on engagement and send the winning version to the remainder of your list. www.mailerlite.com

MailerLite's free-plan details

One important catch: the free plan is currently limited to 250 subscribers, though you get 2,500 emails/month. www.mailerlite.com

If you expect more than 250 subscribers: I'd look at Kit. Kit's free plan supports a much larger audience, and its A/B testing can test two subject lines; testing more than two requires Creator Pro. help.kit.com

My recommendation:

• ≤250 subscribers: MailerLite
• Hundreds/thousands of subscribers and newsletter-focused: Kit
• Large contact database / broader marketing: Brevo, but its full A/B campaign feature is currently on the paid Standard plan. help.brevo.com

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow it down to the best genuinely-free option.

If your main requirement is free A/B testing of email subject lines, I’d try MailerLite first.

My picks

Why MailerLite: its free plan explicitly includes A/B testing, and you can test subject lines, sender information, content, or sending time. It can also automatically send the winning version to the remainder of your audience. www.mailerlite.com

One important distinction: Brevo has A/B testing, including subject lines, but it's not included on the free plan. help.brevo.com

So if you're trying to spend $0 and want to actually learn “which subject line gets more opens?”, start with MailerLite.

See MailerLite's free plan

If you tell me roughly how many subscribers you have and how many emails you send per month, I can narrow it down to the best 2–3 free options for your situation.

If free + actual A/B subject-line testing is the requirement, I’d start with MailerLite.

My picks

MailerLite explicitly says A/B testing is included on all plans, including Free, and you can test subject lines and other campaign elements. www.mailerlite.com

Try MailerLite free

One important caveat: MailerLite's free plan is capped at 250 subscribers and 2,500 emails/month. www.mailerlite.com

If you have more than 250 subscribers, I'd look at your requirements differently. For example, Brevo's free plan supports up to 100,000 stored contacts and 300 sends/day, but its official documentation currently puts A/B testing on the Standard ($18/mo) plan, so it doesn't satisfy your "free A/B testing" requirement. help.brevo.com

Bottom line: If you're under 250 subscribers, MailerLite is the one I'd try first. It gives you the exact thing you're asking for without needing a paid trial.

If you tell me roughly how many subscribers you have and how many emails/month you send, I can narrow this down to the best 2–3 options for you.

If your main requirement is free + A/B subject-line testing, I’d try MailerLite first.

My pick: MailerLite

• Free plan: up to 250 subscribers and 2,500 emails/month. www.mailerlite.com
• A/B testing is included on the free plan, including testing email subject lines. www.mailerlite.com
• You can test up to 5 versions of a single element with A/B testing. www.mailerlite.com
• It reports opens/clicks and can automatically send the winning version to the remainder of your audience. www.mailerlite.com
• The interface is relatively straightforward, so it's a good choice if you don't need a complicated marketing platform.

One caveat: 250 subscribers is the meaningful free-plan limit, despite the 2,500-email monthly allowance. www.mailerlite.com

What about Brevo?

Brevo has a more generous free contact allowance (up to 100,000 contacts), but A/B testing is not included on its free plan. Its free plan is capped at 300 sends/day. help.brevo.com

So for your specific requirement:

Bottom line: Start with MailerLite. It's probably the closest match to "I just want to send emails for free and actually test which subject line performs better."

If you tell me roughly how many subscribers you have and how many emails/month you send, I can give you 2–3 better options based specifically on those numbers.