Cold EmailPopular
Cold email writer
You need to write a B2B cold email that gets replies.
You get Three email variants · Subject lines · Why each angle works
Subject line writer Claude skill
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.
- 4-step play
- 4 guardrails
- 1 file
- Human approval built in
Use it when you need cold email subject lines that get opened and do not look like marketing.
Then just ask your agent
“Write subject lines for this cold email to CFOs.”
Watch it work
One request in, expert work out
What happens when you ask your agent with this skill installed. Every step below comes straight from the skill.
You
Write subject lines for this cold email to CFOs.
Loaded skill
subject-line-writer- Write in the patterns that work for cold B2B
- Follow the format rules
- Give options per pattern
- Test fairly
Subject line options by pattern · Risk notes · Test plan
Ready for your review. Nothing is sent or changed until you approve.
- 4Steps in the play
- 4Guardrails
- 1Files in the skill
- 2 minTo read it all
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.
What you bring
- The email body
- Persona
- Trigger or angle
What you get
- Subject line options by pattern
- Risk notes
- Test plan
name:subject-line-writer
description: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".…
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 eachWhat 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."
Try it
Ask your agent like this
Once the skill is installed, plain requests like these load it automatically. Swap in your own company, buyer and numbers.
-
“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.”
What does the Subject line writer skill do?
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. You get: subject line options by pattern, risk notes, test plan.
When should I use the subject line writer skill?
Use it when you need cold email subject lines that get opened and do not look like marketing.
How do I install Subject line writer in Claude Code?
Run /plugin marketplace add prosyo-ai/gtm-skill and then /plugin install gtm-skills@prosyo to add the whole library, or run npx skills add prosyo-ai/gtm-skill –skill subject-line-writer for this skill alone. In Claude.ai, download the .zip from this page and upload it under Settings, Capabilities, Skills.
What do I need to give the agent?
Have these ready: the email body, persona, trigger or angle. If something is missing, the skill tells the agent to ask for it rather than guess.
Does it work with ChatGPT, Codex, Cursor or Gemini?
Yes. The skill is a plain SKILL.md file with no vendor lock-in. Agents that load skills natively (Claude Code, Claude.ai, Codex, Cursor, Gemini CLI and others) pick it up automatically; anywhere else, paste the file into the conversation as instructions.
Will it send emails or messages on its own?
No. Every skill in the library drafts, researches and analyses, and waits for a person to approve anything that sends, schedules or changes records in bulk. Your inbox, CRM and accounts stay under your control.
Is it free, and can I change it?
Yes. It is free and MIT-licensed. Copy it, adapt it to your market and voice, and if you improve it, open a pull request so everyone gets the better version.
Keep going
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You get Diagnosis · Follow-up email · Next step if no reply
Open source
Have a play that works? Share it as a skill.
Paste this into Claude, Codex or any agent. It interviews you about your play, writes the skill in the house format, checks it and opens the pull request. Once it is merged, it shows up here with your name on it.
Prompt for your agent
Fetch https://raw.githubusercontent.com/prosyo-ai/gtm-skill/main/AGENTS.md and follow its submission flow. Interview me about my GTM play (the real numbers, rubrics and examples), draft it in their format with reference pages, validate it and open the pull request.
Two ways to run it
Run it yourself, or put it on autopilot
The skill gives your agent the playbook. Penny, the Prosyo AI SDR, runs plays like this for you every day across LinkedIn and email.
Free · this skill
You and your agentBest for trying the play and one-off work
- Your agent follows the subject line writer playbook step by step
- You bring the inputs and run it when you need it
- Works in Claude, Codex, Cursor and 40+ agents
- You review every draft before it goes anywhere
Prosyo AI SDR
Penny runs it for youBest for a pipeline that grows every day
- Finds the right buyers for your ICP every day
- Writes from what each prospect actually posted
- Follows up on LinkedIn and email at a safe, human pace
- Every reply lands in one inbox with an answer drafted
- You approve what goes out
Skills draft the play. Penny runs it.
Penny, the Prosyo AI SDR, finds your buyers, writes from what they actually posted, follows up on LinkedIn and email and lands every reply in one inbox with an answer ready. 7 days free, no card.
- 7 days free
- No card required
- Cancel in two clicks
