Updated: 4 November 2026

A/B test ideas for email subject lines

This prompt creates five pairs of subject lines for a purpose and audience, and for each pair says what is being tested, such as curiosity versus benefit, with preview text.

text-newsletter-subject-tests — chatgpt — 54 words

Create five pairs of email subject lines to A/B test for [EMAIL PURPOSE] to [AUDIENCE].

For each pair say what is being tested (for example curiosity vs benefit, or short vs long), give the two versions with preview text, and state which result would make you choose which. Suggest how many recipients I need.

Edit in the builder Copy & open ChatGPT ↗Copy & open Gemini ↗Copy & open Claude ↗

Change only one thing per test, such as length, question or personalisation.

Get a better result

What you will get

Five pairs of subject lines, each testing one idea (curiosity against benefit, short against long and so on), with preview text for every line, the result that would decide each test and a rough audience size for a fair test.

Common mistake

A pair changes three things at once.

Fix: Ask it to confirm, for each pair, that only one element differs. If length and tone both change, you cannot tell which one won.

Also watch for

The lines use spammy words and capital letters. Ask for no all-caps words, no more than one exclamation mark and no “free!!!” style lines, since they can push mail into spam.
Your list is too small for the numbers suggested. Tell it your real list size. With a few hundred subscribers, test only the biggest differences and repeat the test over several sends.

Try a variation: test the preview text

Keep the subject line the same in both versions and test two different preview texts instead, which is easy to overlook.

Still not right? Reply with this

Here are my results so far: [WINNERS, OPEN RATES AND DATES]. What pattern do they show, and what should I test next?