The best email A/B testing tools are the testing features built into your email platform: 
Klaviyo for ecommerce brands that want to pick winners by orders, Mailchimp for multivariate tests with up to eight versions, and 
Omnisend if you want A/B testing on a free plan.
For a quick subject line check before you send, the free Omnisend Subject Line Tester and Mailmeteor Subject Line Tester score a line in seconds, but only a real A/B test tells you what your list will open and click.
How we picked: we read each vendor's public docs and pricing pages, checked public ratings where a review site showed them, and matched each tool to email tests in our archive. We have not used these tools ourselves.
One note on money: we may earn a commission if you sign up for Omnisend through our links.
None of the other tools on this page pay us.
Email A/B testing tools compared
| Tool | Best for | Starting price (as of November 2026) | Free plan or trial | Rating (source) |
|---|---|---|---|---|
| Klaviyo | Ecommerce brands testing campaigns and flows | Email plan $20/mo for 251-500 contacts | Free plan (250 active profiles, 500 sends/mo) | 4.7/5, 3,430 reviews (Shopify App Store) |
| Mailchimp | Small teams that want multivariate tests | Standard $20/mo for 500 contacts; A/B testing starts on Essentials | Free plan (no A/B); 14-day Standard trial | 4.8/5, 1,558 reviews (Shopify App Store) |
| Omnisend | Ecommerce on a tight budget | Standard $16/mo for 500 contacts | Free plan includes A/B testing | 4.7/5, 3,201 reviews (Shopify App Store) |
| Brevo | Cheap volume sending with basic tests | Standard $18/mo billed monthly (A/B testing starts here) | Free plan, 300 emails/day | Not checked |
| ActiveCampaign | Testing inside automations | Starter $15/mo billed yearly, 1,000 contacts | Free trial | Not checked |
| HubSpot Marketing Hub | B2B teams already on HubSpot CRM | Professional $800/mo (A/B testing tier) | Free tools, no email A/B | Not checked |
| MailerLite | Newsletters, creators and small sites | Comfort $12/mo for 500 subscribers | Free plan with A/B testing | Not checked |
| Omnisend Subject Line Tester | Free pre-send subject line check | Free | No account needed | Not rated |
| CoSchedule Headline Studio | Writers who score subject lines and headlines | Basic plan free; Premium paid | Free Basic plan | Not checked |
| Mailmeteor Subject Line Tester | Free score plus AI rewrites | Free (fair use) | No signup | Not rated |
Prices change with list size. Every price above is the entry point on the vendor's own page; your bill will be higher once your list grows.
The 10 best email A/B testing tools and subject line testers
Entries 1-7 are email platforms with built-in split testing.
Entries 8-10 are subject line testers that score a line before you send it.
Use both: the tester to clean up a draft, the platform to find out what your list actually does.
1. Klaviyo
Best for: ecommerce brands that want to judge email tests on revenue, not just opens.
What it does: Klaviyo is an email and SMS platform built around store data.
You can A/B test campaigns and individual flow emails, and campaign tests can pick a winner by open rate, click rate or placed order rate.
Key features:
- Campaign A/B tests with two or more variations; the winner is sent to the rest of the list
- A/B testing inside flows such as welcome and abandoned cart series
- Placed order rate as a winning metric
- Email and SMS tests in one tool
Pros:
- Lets you pick winners by orders, which avoids "more opens, fewer sales" results
- Deep ecommerce data for segments
- Free plan to start
Cons:
- Costs climb quickly as active profiles grow
- Built for ecommerce; SaaS and lead-gen teams use few of its best features
- Free plan email support lasts only the first 60 days
Pricing: free up to 250 active profiles and 500 email sends a month.
The Email plan is listed at $20/month for 251-500 contacts on Klaviyo's Shopify App Store listing; see Klaviyo pricing for larger lists.
Rating: 4.7 out of 5 from 3,430 reviews on the Shopify App Store.
In our archive: the reason to judge by orders or clicks.
A curiosity subject line got +12.7% opens but fewer unique clicks, so MarketingExperiments counted it as a loss.
2. Mailchimp
Best for: small businesses and nonprofits that want simple A/B tests, plus multivariate tests once they grow.
What it does: Mailchimp is a general email platform used by every kind of business.
Its A/B tests cover subject lines, design, content and send times, and higher plans add multivariate tests with up to eight campaign versions.
Key features:
- A/B tests on subject line, design, content and send time
- Multivariate testing with up to eight variations on Standard and Premium
- Works for ecommerce, SaaS, lead gen and nonprofits
Pros:
- Easy to set up for first-time testers
- Multivariate testing at a mid-range price
- Large integration library
Cons:
- No A/B testing on the Free plan
- Multivariate is not on Essentials
- Prices rise in steps as contacts grow
Pricing: A/B testing is included on Essentials, Standard and Premium, per Mailchimp's plan comparison.
Standard starts at $20/month for 500 contacts with a 14-day free trial (Mailchimp pricing).
Rating: 4.8 out of 5 from 1,558 reviews on the Shopify App Store.
In our archive: the kind of test multivariate suits.
MECLABS Institute tested several subject line themes for VolunteerMatch; network-size lines got a -12.5% click rate against passion-led lines.
3. Omnisend
Best for: ecommerce brands that want A/B testing without paying first.
What it does: Omnisend is an email, SMS and push platform for online stores.
Its email A/B testing is on every plan, including Free, and it runs the free subject line tester in entry 8.
Key features:
- Campaign A/B testing on all plans
- Pre-built ecommerce flows such as welcome and cart abandonment
- Email, SMS and web push in one place
- 24/7 live chat and email support on every plan
Pros:
- A/B testing on the Free plan
- Lower entry price than Klaviyo
- Free migration from another platform
Cons:
- The Free plan sends only 500 emails a month to 250 contacts, too few for a meaningful test
- Ecommerce focus; not a fit for SaaS or B2B lead nurturing
- The 30% discount on the pricing page only applies if you pay three months upfront; after that you pay the full monthly price
Pricing: Free; Standard $16/month for 500 contacts; Pro $59/month for 2,500 contacts; both are 30% off if you pay three months upfront (Omnisend pricing).
Omnisend has an affiliate program, so we may earn a commission if you sign up through our link.
Rating: 4.7 out of 5 from 3,201 reviews on the Shopify App Store.
In our archive: a flow worth testing. CNET's series of simpler welcome emails moved opens from 32% to 46% and clicks from 12% to 21%, across several bundled changes.
4. Brevo
Best for: businesses that send a lot of email on a small budget and only need basic tests.
What it does: Brevo (formerly Sendinblue) is an email, SMS and CRM platform priced on email volume.
A/B testing of subject lines or content starts on the Standard plan.
Key features:
- A/B tests on subject lines or content
- AI send time optimization on Standard
- Click heatmaps in email reports
Pros:
- Low price for high send volume
- Free plan to try the editor and sending
Cons:
- No A/B testing on Free or Starter
- Big price jump from Standard to Professional ($499/month billed monthly)
Pricing: Free plan up to 300 emails a day; Starter $9/month; Standard $18/month billed monthly or $16.17 billed yearly (Brevo pricing).
In our archive: a small test that needed a rerun.
Apollo Education Group's name in the preheader lifted opens +9%, but only on the second run; the first run did poorly.
5. ActiveCampaign
Best for: SaaS, B2B and service businesses that want to test steps inside automations.
What it does: ActiveCampaign is a marketing automation platform with a built-in CRM option.
Campaign A/B testing is on every plan, and Pro and Enterprise add split testing inside automations.
Key features:
- Campaign A/B testing on all plans
- Automation split testing on Pro and Enterprise
- Predictive sending and conditional content on Pro
Pros:
- Strong automation builder for nurture sequences
- Good fit for lead gen and SaaS onboarding
- 30-day money-back guarantee
Cons:
- Automation tests need Pro, $79/month billed yearly
- Starter and Plus test email campaigns only
- Less ecommerce-specific than Klaviyo or Omnisend
Pricing: Starter $15, Plus $49, Pro $79 and Enterprise $145 per month, billed yearly for 1,000 contacts (ActiveCampaign pricing).
In our archive: why sequences are worth testing.
HomeAdvisor's project-matched follow-up emails got 2x conversion and 1.5x clickthrough.
6. HubSpot Marketing Hub
Best for: B2B and SaaS teams that already run their CRM on HubSpot.
What it does: HubSpot's marketing emails can be A/B tested on a share of your list, with the winner chosen by open rate, click rate or click-through rate and sent to everyone else.
A/B testing is on the Professional and Enterprise tiers.
Key features:
- Set the test sample, test length and a fallback version
- A/B tested emails inside workflows
- Results tied to CRM contacts and deals
Pros:
- Email results sit next to pipeline data
- Clear setup steps in HubSpot's own docs
Cons:
- A/B testing needs Professional, from $800/month
- Expensive if you only need email
- HubSpot recommends at least 1,000 contacts per A/B test email
Pricing: Free tools; Starter from $7/month per seat; Professional from $800/month with three core seats; Enterprise from $3,600/month (HubSpot pricing).
In our archive: a B2B subject line win.
AppVault named the prospect's applicant tracking system in the subject line and opens went from 13% to 66%.
7. MailerLite
Best for: newsletters, creators and small sites that want testing on a free plan.
What it does: MailerLite is a simple email platform with landing pages and forms.
A/B testing is available to all users; multivariate testing (up to 8 versions across 3 elements) is on Comfort and Power.
Key features:
- Test subject lines, content, sender names and send times
- Winner sent to the rest of the list automatically
- A/B testing for forms and landing pages too
Pros:
- A/B testing on the Free plan
- Low paid prices
- 14-day trial of premium features
Cons:
- Free plan caps at 250 subscribers and 2,500 emails a month
- Lighter ecommerce data than Klaviyo or Omnisend
Pricing: Free; Comfort $12/month and Power $25/month for up to 500 subscribers, billed monthly (MailerLite pricing).
In our archive: a newsletter test that lost.
Using the first article's headline as the preheader cut clicks by -12% for MarketingExperiments.
8. Omnisend Subject Line Tester
Best for: a free check of any subject line, whatever platform you send from.
What it does: paste a subject line and the tester scores it from 0 to 100% on length, wording and scannability.
It flags spam-prone words and shows a mobile and desktop preview.
Key features:
- 0-100% score with suggestions
- Spam word and helpful word flags
- Mobile and desktop inbox previews
Pros:
- Free, no account needed
- Fast enough to check every send
Cons:
- Scores generic rules, not your audience
- Can't tell you which line drives clicks or sales
Pricing: free.
In our archive: why a score is only a start.
The Global Leadership Summit expected a star speaker's name to win, but "13 world-class speakers" won again and again (no figures were shared).
9. CoSchedule Headline Studio
Best for: content teams who write blog headlines and email subject lines and want one scoring tool.
What it does: CoSchedule's email subject line tester gives an overall score based on length, keywords and character count, then breaks it down by word balance, skimmability and sentiment.
It is part of Headline Studio, which also scores headlines for the web, YouTube and social.
Key features:
- Overall score plus word balance and sentiment
- Version history of past subject lines and scores
- Works for headlines and captions too
Pros:
- Free Basic plan
- Useful word-level feedback for writers
Cons:
- Needs an account and uses a credit system
- Rewards "power words" that may not suit your brand
Pricing: Basic is free; Premium is paid (Headline Studio pricing).
In our archive: list-style lines are not a sure thing.
A "Top 10 insights" email got about -80% clicks against general copy in a MECLABS test.
10. Mailmeteor Subject Line Tester
Best for: getting a score and a few AI-written alternatives to test.
What it does: the Mailmeteor tester checks format, length, emoji use and spam words, gives a score out of 100, and suggests rewrites. It is free with no signup.
Key features:
- Score out of 100
- Spam word and emoji checks
- AI-generated alternative subject lines
Pros:
- Free and no signup
- Gives you variants to put into a real A/B test
Cons:
- Fair-use limits apply
- AI rewrites can sound generic
Pricing: free.
Which one is right for you
Ecommerce brands
Klaviyo if you want to judge tests by orders and test inside flows.
Omnisend if you want A/B testing on a cheaper plan.
See our guide to cart abandonment emails for flows worth testing first.
SaaS and B2B
ActiveCampaign for testing automation steps; HubSpot if your CRM is already there and you can pay for Professional. More ideas in SaaS email tests.
Lead gen, nonprofits and newsletters
Mailchimp for multivariate tests, MailerLite for a free plan with A/B testing.
Browse lead-gen email tests for what has worked.
No budget
MailerLite or Omnisend free plans for real tests, plus the Omnisend or Mailmeteor tester before each send.
For free website testing tools, see free A/B testing tools.
What to look for
- Winning metric: can it pick a winner by clicks or orders, not only opens?
- Flow testing: can you test welcome, cart and onboarding emails, not just one-off campaigns?
- Plan gate: check which plan unlocks A/B testing; on Mailchimp, Brevo and HubSpot it is not the cheapest one.
- Test sample and length: you should control what share of the list gets the test and how long it runs.
- Number of variations: two is enough for most tests; multivariate needs a large list.
- Reporting: look for results you can export or tie to revenue, not just a winner badge.
- Price at your list size: compare the price at your real contact count, not the starting price.
Real email test results
These are email tests from our archive, including ones that lost. More in our email A/B testing guide.
MarketingExperimentsNot every email test needs an email platform.
EnergySage signed its account verification email with a real team member's name and approved properties rose +3.98%, in a server-side test run on 
VWO.
Watch out for
- Open rates as the only goal. Apple Mail Privacy Protection and image blocking make opens noisy, and a line that wins opens can lose clicks, as the curiosity test above did.
- Small lists. A test on a few hundred contacts rarely shows a real difference. Check with our sample size calculator and significance calculator.
- Short test windows. Most tools let you send the "winner" after a few hours. Morning opens may not match the whole day.
- Trusting a score over a test. Subject line scores follow general rules. Your list may disagree.
- One-off wins. Apollo's preheader test did poorly the first time and won on the retest. Rerun big wins before you change every email.
For website and app testing tools, see our A/B testing tools roundup or the full tools hub.