Optimize · Subject-Line & A/B Variants

Generate 10 Subject Line Variants for a Cold Email

Turn one cold email body into 10 inbox-safe, testable subject line variants with per-variant rationale.

foundermanagerrepBeginner⏱ 30-45 min
When to use
Use this when you have a cold email body you like but the subject line is dragging open rates down. It produces 10 deliverability-safe variants, each testing a different lever (curiosity, specificity, personalization, social proof, pain, etc.) so you can ship a real A/B test instead of guessing. Best run before loading a new sequence into Instantly, Smartlead, or Apollo.
The prompt
You are a cold-email specialist for a digital marketing agency. You know inbox psychology and the rules of outbound deliverability — short, lowercase, no spam triggers, no clickbait, no fake Re:/Fwd:.
Agency: [AGENCY_NAME] — [SERVICES] | Email body: [EMAIL_BODY] | Prospect: [PROSPECT_NAME] at [PROSPECT_COMPANY] | ICP: [ICP_DESCRIPTION] | Current best subject + open rate: [CURRENT_SUBJECT] / [CURRENT_OPEN_RATE]
Write 10 cold email subject line variants for the email body above. Each variant must test a DIFFERENT psychological lever so the A/B test produces a real signal.

- Max 6 words OR 45 characters, whichever hits first
- All lowercase except proper nouns; no emoji; no clickbait; no "Quick question"; no fake Re:/Fwd:
- No spam-trigger words (free, guarantee, $$$, !!!)
- Each of the 10 variants tests a different lever: curiosity, specificity/metric, personalization, pain point, social proof, trigger event, question, contrarian, benefit, ultra-short
- Must be honest to the email body — no bait-and-switch

Numbered list 1-10. Format per line: " — lever:  — rationale: ". Put the variant you'd ship as the A/B winner candidate first and label it (WINNER).
Variables
  • [AGENCY_NAME] — Your agency name
  • [SERVICES] — What you sell (SEO, paid social, web design, etc.)
  • [EMAIL_BODY] — Paste the full cold email body the subject must fit
  • [PROSPECT_NAME] — First name of the prospect
  • [PROSPECT_COMPANY] — Prospect's company name
  • [ICP_DESCRIPTION] — 1-line description of who this email targets
  • [CURRENT_SUBJECT] — The subject you're currently using
  • [CURRENT_OPEN_RATE] — Current open rate %, e.g. 24%
Example input
Agency: NorthLoop — SEO + content for B2B SaaS | Email body: 90-word note offering a 15-min audit of their top 3 commercial pages | Prospect: Maya at Klario | ICP: Series A-B SaaS doing content marketing in-house | Current subject: "quick SEO question for klario" / 21%
Example output
1. klario's /pricing page (WINNER) — lever: specificity — rationale: names a page Maya owns; feels like a real audit, not a pitch.
2. saw klario ranking #6 — lever: trigger event — rationale: implies you looked; opens curiosity loop.
3. 3 fixes for klario seo — lever: benefit — rationale: promises value, count tightens it.
4. maya, quick thought on klario — lever: personalization — rationale: name + company, no fake urgency.
5. klario vs default tag — lever: contrarian — rationale: hints at a specific finding.
6. you missed a meta on /signup — lever: pain — rationale: concrete, mildly uncomfortable.
7. how rippling 4x'd organic — lever: social proof — rationale: peer SaaS reference.
8. one page, one fix? — lever: question — rationale: low-commit ask.
9. seo audit for klario — lever: ultra-short — rationale: clean control variant.
10. klario's content gap — lever: curiosity — rationale: vague enough to open, honest to body.
Pro tips
  • Always ship the WINNER + one ultra-short variant as your A/B — short wins more than people admit.
  • Test only 2 variants at a time per sending mailbox; more splits the sample too thin.
  • Re-run this prompt after 500 sends per variant — the losing lever often tells you what your ICP doesn't care about.
Works with
ClaudeChatGPTGemini
Done with prompts? Time to install the system
Book a STAOS call
Related prompts