🧪 Cold Email A/B Test Designer
Pick what you're testing, paste your control, and get three variants — plus the sample size you need, the metric to track, and rules for when to call a winner.
Set up the test
Test one variable at a time — otherwise you can't attribute the lift.
Your test plan
Your test design will appear here
Fill in the form and click Design the test
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Frequently asked questions
How big does each test arm need to be?+
It depends on four things: your baseline reply rate, the smallest lift you want to detect, your confidence level (usually 95%), and statistical power (usually 80%). As a rough illustration, detecting a 30% relative lift on a ~5% baseline at those settings takes on the order of a few thousand sends per variant — small lifts on low baselines need far more volume than people expect. The tool calculates the exact number from your inputs and shows the math.
Should I test subject line and opener at the same time?+
No. Test one variable at a time. If you change both, you can't attribute the lift (or drop) to either. The tool enforces this — pick subject OR opener and lock the other.
What metric should I track?+
For subject-line tests: open rate (or reply rate if you don't track opens reliably — open tracking is increasingly unreliable with Apple Mail Privacy Protection). For opener tests: reply rate. The tool tells you which one matches your variable.
When can I call a winner?+
Only after every variant has hit the calculated sample size AND the difference exceeds the minimum-detectable-effect threshold (typically a 30% relative lift). Calling winners early on small samples is the most common mistake in cold email testing.
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