Cold Email Subject Line Tester
Analyze your cold email subject lines for length, spam triggers, and personalization. Preview exactly how your email will look on an iOS mobile lock screen.
Mobile Lock-Screen Simulator
80% of cold emails are judged and deleted directly from a phone's lock screen. Use the simulator on the right to see exactly how your subject line and preview text will truncate on an iPhone before you hit send.
What is the Cold Email Subject Line Tester?
Score your subject lines and preview exactly how they will truncate on an iOS Lock Screen before you hit send. Built for optimal performance, this tool executes client-side directly in your browser without uploading your sensitive data to external servers.
How to use the Cold Email Subject Line Tester
- Type or paste your candidate cold email or newsletter subject line.
- The analyzer scores your subject line based on character length, word count, spam trigger words, and personalization tokens.
- Inspect the live mobile and desktop inbox previews to check where your subject line will get cut off.
- Review concrete recommendations to improve open rates and avoid spam filter traps.
Example: Testing a B2B Outreach Subject Line
Quick question regarding your Next.js architecture
Score: 92/100 | Length: 49 chars (Safe on iOS Mail & Gmail) | Spam Words: 0
Ensures subject lines stay under 50 characters to prevent truncation on mobile smartphone lock screens.
Technical Guide & Privacy Assurance
Avoid using all-caps, excessive punctuation (like '???!!!'), and spam trigger words ('FREE', 'GUARANTEED', 'ACT NOW') which trigger algorithmic email quarantine filters.
Frequently Asked Questions
Why is the lock-screen preview important?+
80% of cold emails are read on mobile devices. If your subject line and preview text are too long, they will be cut off, ruining the hook.