subject-line-writer
Use this skill when you need cold email subject lines that get opened and do not look like marketing: "write subject lines for this email", "my open rates are low", "A/B test subject lines". Writes short, lowercase, internal-looking subject lines matched to the email's angle, explains the pattern behind each, flags spam and clickbait risks, and sets up a fair subject-line test. For cold outreach, follow-ups and re-engagement emails.stars—
forks—
watches—
updatedNot available
Use this after the email is written. The subject line's job is to get the email opened by the right person without promising something the body does not deliver.
Inputs
- The email body (subject lines are written for a specific email, never in a vacuum).
- The persona and seniority.
- The trigger or angle the email uses.
The play
1. Write in the patterns that work for cold B2B
| Pattern | Example | When |
|---|---|---|
| Topic, two to four words | "month-end close" | Default |
| Trigger reference | "new sdr team", "the series b" | Email leads with a trigger |
| Peer or customer | "contoso's close" | Strong, approved proof |
| Question | "manual reconciliations?" | Pain is very common |
| Their initiative | "europe expansion" | Announced plan |
| Mutual context (only if real) | "maria suggested i reach out" | Genuine referral |
2. Follow the format rules
- 1 to 5 words; under 40 characters so it is not cut on phones.
- Lowercase or sentence case; it should look like it came from a colleague.
- No first-name merge field in the subject (it reads as automated), no emojis, no exclamation marks, no "quick question".
- The subject must be true to the email. Clickbait wins opens and loses replies and trust.
3. Give options per pattern
Return 2-3 options for 3 patterns. Mark the recommended one.
4. Test fairly
- Change only the subject; keep body, list and send time the same.
- At least 200 sends per variant before judging.
- Judge on reply rate, not opens. Open tracking is unreliable: privacy features pre-load images and inflate opens, and many teams disable tracking pixels to protect deliverability.
Output format
Recommended: <subject>
Topic: <3 options>
Trigger: <3 options>
Question: <3 options>
Avoid: <any risky phrasing found and why>
Test: A = <..>, B = <..>, judge on reply rate after 200+ sends each
What good looks like
- Reads like a peer's email in a crowded inbox.
- Connects directly to the first line of the email.
- No spam-pattern words: "free", "guarantee", "act now", "limited time", percentages off.
- The common mistake is clever or vague subjects ("thoughts?", "a crazy idea") that get opened out of curiosity and then deleted with irritation.
Rules
- MUST keep subject lines under 40 characters.
- MUST match the subject to the email's actual content.
- NEVER use fake reply or forward prefixes ("Re:", "Fwd:") on a first email.
- NEVER use a referral subject unless the referral is real.
Example prompts
- "Write subject lines for this cold email to CFOs."
- "Give me 10 subject lines for a follow-up that shares a case study."
- "Set up a subject line test for our new campaign."