Email Subject Line Tester
Analyze cold subject lines, predict click rates, and optimize using AI.
How it works: Type your subject line, select your target persona and tone, hit Analyze Subject, and get an instant AI-powered breakdown of where your subject line is failing — plus step-by-step rewrites to fix it.
1Configuration Settings
2Diagnosis Mode
Subject Line Guidelines
Optimal Length
Keep it between 40 and 60 characters. Subject lines that are too long will be truncated in mobile inbox previews.
Avoid Spam Triggers
Do not use aggressive sales words like 'free', 'guaranteed', 'act now', or excessive punctuation (!!!, $$$). These trigger junk mail filters.
Readability Level
Use simple, direct language. Subject lines written at a 5th-grade reading level typically receive the highest open rates.
Personalization
Include contact's first name or company name using merge tags (e.g. {{first_name}}). Personalized lines receive up to 26% higher open rates.
3Subject Line Composition
Your Diagnosis Results Will Appear Here
Did you know? Subject lines with 40-50 characters have the highest open rates. Type your subject line, select target personas/tones above, and analyze to see spam risk, readability, and AI-driven optimizations.
Confidence Disclaimer
The output is an estimate, not a guarantee. (Results are based on industry benchmarks and estimated conversion improvements. Actual results may vary.