cold-email-subject-line-tester

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---
name: cold-email-subject-line-tester
description: Generates, scores, and split-tests email subject lines, producing angle-distinct variants, a numeric scorecard, and a test plan with sample size and decision metric. Covers B2B cold outbound and B2C lifecycle/promotional email, and flags spam-trigger words inside the subject line only. Use whenever the user mentions a subject line, open rates, email A/B test, preview text, or "nobody opens my emails", even if they don't say "subject line" explicitly. Do NOT use for body copy or inbox-placement audits (mbfinotti/sales-skills@cold-email-deliverability), personalization angles (mbfinotti/sales-skills@sales-outreach-personalization), or cadence design (mbfinotti/sales-skills@sales-outbound-sequence).
license: MIT
metadata:
  author: Maya-Beth Finotti
  version: "1.4.3"
---

# Subject Line Tester

Generate subject line variants from an already-chosen personalization angle, score them against a numeric rubric, and design a statistically honest split test to pick the winner.

Two facts frame everything here:

- No named, cross-source framework exists for subject lines the way MEDDIC exists for qualification - only single-vendor branded methods and one unbranded convergence (keep B2B cold subjects short; avoid numbers and question marks in them).
- Nearly every published subject-line statistic comes from companies selling email tooling, none of it independently audited: trust the direction, never the magnitude.

Where sources flatly contradict each other (notably lowercase vs. title case), treat the question as a test candidate, never a rule.

Scope: the subject line (plus preheader for B2C) is the whole deliverable.

Never:

- Write body copy.
- Audit deliverability, headers, domains, or authentication.
- Research prospect signals.
- Plan touch-by-touch cadence.

Flag spam-trigger vocabulary inside the subject itself as a scoring check, then hand the full inbox-placement review to `mbfinotti/sales-skills@cold-email-deliverability`.

## Interview

Ask one question per message. Offer multiple-choice options. Skip anything already answered by context. If your harness has persistent memory and a prior run stored this user's answers, confirm them instead of re-asking.

1. Regime: B2B cold outbound, or B2C lifecycle/promotional? Ask this first - the two follow different rules.
2. Recipient persona, role, and seniority? Executive inboxes decide in seconds; the pattern set narrows sharply for them.
3. Which personalization angle is already chosen - pain point, competitor, company initiative, executive priority, shared context, trigger event? If none, stop and route to `mbfinotti/sales-skills@sales-outreach-personalization` first. Ranking these is step 4's job, not this question's.
4. What does the email body actually promise or deliver? The subject must never outrun it.
5. Can your sending platform (sequencer or ESP) split-test? At what volume (list size or sends per day)?
6. Which decision metric can you trust in your setup: replies or meetings, clicks or conversions, or only opens?
7. By what date must the result land? A deadline inside the week promotes the near-zero-research angles and cuts the parked-question tests entirely; a date far enough out to collect 200+ sends per variant keeps a test in scope.
8. One-off win on this campaign, or a compounding asset? Compounding promotes the reusable angles (internal-style noun, persona pain, executive anchor) and the casing test; one-off promotes whichever angle today's list already supports.
9. Effort ceiling: how many research minutes per prospect are affordable, and how many sends per day are available? Near-zero minutes deletes the trigger-event, competitor and initiative angles outright; a quota too small to reach the per-variant floor deletes the test queue.
10. B2C only: do you control the preheader text, and is emoji acceptable to the brand?

Re-rank the angle catalog against the answers to 7-9 before drafting, and tell the user whic