Email
A/B Test Subject Line Prompt Template
This subject line A/B test prompt generates matched pairs testing one variable at a time. Get clean results and learn what your list loves. Try it today.
The prompt
Role: You are an email optimization specialist who designs clean A/B tests. You know a good test changes exactly one variable so the winner teaches you something. Context: My email is about [EMAIL_TOPIC] for [AUDIENCE]. My current control subject line is [CONTROL_LINE], which got [CONTROL_PERFORMANCE]. I want to test this variable: [TEST_VARIABLE], for example tone, length, personalization, curiosity versus clarity, or emoji versus no emoji. Task: Generate 5 A/B test pairs. Each pair keeps everything the same except the one test variable, so results are readable. For each pair, label which is A (control style) and B (challenger), state the hypothesis in one sentence, and note what a win for B would teach us. Format: 5 numbered pairs, each with A line, B line, hypothesis, and learning. Then recommend which pair to test first and why. Constraints: Every line under 50 characters. Only one variable changes per pair. Hypotheses must be specific and falsifiable. No spam trigger words. Keep suggestions realistic for a list of [LIST_SIZE] subscribers.
Variables to fill in
Replace each [variable] in the prompt with your own details:
[EMAIL_TOPIC] [AUDIENCE] [CONTROL_LINE] [CONTROL_PERFORMANCE] [TEST_VARIABLE] [LIST_SIZE]
Example input
EMAIL_TOPIC: new feature launch; AUDIENCE: existing customers; CONTROL_LINE: New: one-click reports are here; CONTROL_PERFORMANCE: 32% open rate; TEST_VARIABLE: curiosity vs clarity
How to use this prompt
Test one pair at a time on a random 20 percent sample, wait 4 hours, then send the winner to the remaining 80 percent. Record what you learn for future sends.
Tips for the best results
- Change one variable per test or the result teaches nothing.
- You need a few hundred opens per variant for a meaningful read.
- Test subject lines first: they move the needle most.
Frequently asked questions
How long should I run a subject line test?
Four to six hours is usually enough for most of your opens to land. Then send the winner to the rest of the list the same day.
What should I test after subject lines?
Preview text, then send time, then the CTA button. Work down the email in order of impact on the click.