Cold Email Subject Line Tester
Free cold email subject line tester — paste your subject line and get a score for length, spam triggers, personalisation, and curiosity gap.
About this tool
Scores subject lines on four dimensions that correlate with open rates: length (3–8 words is optimal), spam trigger words, personalisation tokens, and curiosity gap signals. Runs locally.
Frequently Asked Questions
- How long should a cold email subject line be?
- 3–8 words. Subject lines over 60 characters get truncated on mobile, where 60%+ of B2B email is read.
- What are spam trigger words to avoid?
- 'Free,' 'guarantee,' '$$,' 'urgent,' excessive ALL CAPS, and excessive punctuation are the worst offenders. The tester flags the rest.
- Does personalisation actually improve open rates?
- Yes — subject lines with a specific personalisation token (company name, role, recent trigger) open at roughly 1.5–2× the rate of generic subject lines in most B2B cohorts.