Subject Line Tester
Preview how your email subject lines appear in Gmail, iOS Mail, and Outlook. See exact truncation behavior across mobile and desktop clients.
Try examples:
Gmail Mobile
~37 chars
S
Sender Name
12:34 PM
Subject line preview...
Preheader text appears here
Gmail Desktop
~70 chars
Sender Name
Subject line preview...
- Preheader text
12:34 PM
iOS Mail
~48 chars
Sender Name
12:34 PM
›
Subject line preview...
Preheader text appears here after the subject
Outlook Mobile
~40 chars
S
Sender Name
12:34 PM
Subject line preview...
Preheader text appears here
Features
- Visual preview across 4 email clients: Gmail Mobile, Gmail Desktop, iOS Mail, and Outlook Mobile
- See exact character truncation with ellipsis matching real client behavior
- Live character count with color-coded status (green/yellow/red)
- Dark mode toggle for each preview
- Example subject lines demonstrating truncation issues
- Works entirely in your browser - no data sent to servers
Character limits by client
| Client | Mobile | Desktop |
|---|---|---|
| Gmail | ~37 chars | ~70 chars |
| iOS Mail | ~48 chars | ~78 chars |
| Outlook | ~40 chars | ~60 chars |
How to use
- Enter a sender name (or use the default)
- Type your subject line and watch the character count
- Add optional preheader/preview text
- View all 4 client previews simultaneously
- Toggle dark mode on any preview to check appearance
- Click example subject lines to test truncation scenarios
Character count indicators
- Green: Within safe limit (≤37 chars) - displays fully on all mobile clients
- Yellow: May truncate on some mobile (38-50 chars) - test carefully
- Red: Will truncate on most mobile (>50 chars) - consider shortening
Tips
- Front-load important words - they’ll always be visible
- Test with preheader text to see the full inbox row appearance
- Mobile character limits vary by device width - these are typical values
- Emojis count as 1-2 characters depending on the client