Subject Line Lab
Generate and screen cold email subject lines against truncation, spam triggers and the preview text they create.
Free
Works with the AI tools you already use
Claude Code
Cursor
Codex CLI
GitHub Copilot
Gemini CLI+20 moreClaude CodeCursorCodex CLIGitHub CopilotGemini CLI
OpenClaw
Manus
Grok+17 agentsSubject Line Lab
Example session with this skill installed
Write subject lines for this email to VPs of Sales about our new lead data tool. The first line is: I noticed your team is hiring three new SDRs this month.
- Read your context and instructions
- Compiled the subject line lab
| Subject | 30ch | 45ch | Preview | Test |
|---|---|---|---|---|
| Question about the 3 SDRs | Question about the 3 SDRs | Question about the 3 SDRs | I noticed your team... | Specificity |
| SDR hiring | SDR hiring | SDR hiring | I noticed your team... | Brevity |
Connects securely to your tools. The creator never sees your data.
About this skill
Generate and screen cold email subject lines against truncation, spam triggers and the preview text they create. Use when someone needs subject lines, has low open rates, or wants to test subject variants.
Every free skill sits on a 30 day review cycle. Fixes and improvements ship as repo updates. Free forever. The premium version of this workflow lives in the Cold Email System Pack at mambabuilt.com.
How to install
Works the same in every agent - Claude, Cursor, Codex, Copilot and 20+ more.
- 1
Download the ZIP
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- 2
Unzip into your skills folder
Every agent reads skills from one folder on your machine. Drop the unzipped folder in there.
- 3
Ask your agent to use it
Restart the agent if it was already running. It picks the skill up automatically - no config needed.
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Click the path to copy it. Create the folder if it does not exist yet.
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