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Marketing & Content

Subject-Line A/B Variant Generator

Every email campaign gets 6 subject lines as a ready A/B test pack.

Saves about ~30 min per week

What it does

  • Takes your campaign topic and audience once
  • Generates 6 subject lines across proven styles
  • Keeps them under length limits per platform
  • Outputs them ready for your A/B test setup

How it works

  1. Campaign brief fed in
  2. AI drafts 6 subject lines in different styles
  3. Lines output with hook-type labels
  4. You pick the pair to test

What's included

  • Brief template
  • 6-style generator
  • A/B test pack

Set it up yourself

Follow these 4 steps in order. You will need accounts for: Gmail, Claude.

Step 1: Write the brief fields

  1. Create the brief inputs: topic (the email's promise), audience, tone, and 1-2 proof points.
  2. Save the brief as a reusable workflow template.
  3. Keep the offer and deadline out of the subject unless you want them tested.
  4. Test that the workflow accepts a brief and produces one row per line.

Watch out: A concrete promise in the brief beats a vague topic — 'recover 10 hours' generates sharper subjects than 'productivity hacks'.

Step 2: Add the subject prompt

  1. Build: 'Draft 6 subject lines for this email. Styles: 1 curiosity, 2 benefit, 3 social-proof, 4 question, 5 urgency (light), 6 specific-number. Under 45 chars each (under 30 for SMS). Return JSON array with style and subject.'
  2. Add: no clickbait, no ALL CAPS, match {tone}.
  3. Paste with API key.
  4. Test on the brief.
  5. Check character counts.

Watch out: Style labels matter — they tell you which variant won so future briefs can lean into winners.

Step 3: Export the test pack

  1. Output the 6 lines to a sheet/section with Style and Subject columns.
  2. Pick the 2 most different lines for your A/B test (don't test near-identical ones).
  3. Paste them into your mail platform's A/B test fields.
  4. Split 50/50 for a clean read (or send 10% to whichever needs data).
  5. Run until the winner is statistically clear.

Watch out: Testing two identical-phrasing lines wastes the test — choose the most stylistically distinct pair.

Step 4: Log the results

  1. Record winner by style in a 'Subject Winners' sheet.
  2. After 10 tests, review which styles win for which audiences.
  3. Feed the pattern back into the brief prompts (charge the prompt 'strongest in this niche was question-type').
  4. Retire styles that consistently lose.
  5. Refresh quarterly.

Watch out: The feedback loop is the pay-off — a log of 10 tests is worth more than any single variant.

Frequently asked questions

What does the Subject-Line A/B Variant Generator automation do?

Every email campaign gets 6 subject lines as a ready A/B test pack. Takes your campaign topic and audience once

How much time does Subject-Line A/B Variant Generator save?

It is estimated to save ~30 min per week. Actual savings depend on your volume.

Which tools does Subject-Line A/B Variant Generator use?

It works with Gmail and Claude.

What does Subject-Line A/B Variant Generator include?

Brief template, 6-style generator, A/B test pack.

Can I set up Subject-Line A/B Variant Generator myself?

Yes. The do-it-yourself guide on this page walks through 4 steps, from getting access to testing the finished automation.