ChatGPT answers, unedited

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.