Free Email Subject Line Tester
Preview subject lines across mobile and desktop inboxes before your next campaign.
A strong email subject line has to survive a crowded inbox before anyone reads the campaign. Test the hook, check the visible mobile preview, and pair it with supporting preview text before you send.
- Preview mobile and desktop truncation
- Check subject and preview text length
- Catch repeated punctuation and all caps
- Flag common promotional trigger words
- Useful for newsletters, launches, and cold outreach
- Free, no login required
Start typingAim for a clear hook in the first 40 characters, then use preview text for supporting detail.
Subject characters
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Subject words
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Preview characters
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Mobile inbox
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Your subject line appears here
Preview text appears here when you add it.
Desktop inbox
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Your subject line appears here
Preview text appears here when you add it.
Suggestions
- Write a clear subject line before checking the inbox preview.
How to Test an Email Subject Line
- Paste your subject line and read the mobile preview first.
- Add preview text to support the hook instead of repeating it.
- Rewrite the first words until the main value appears before the truncation point.
When This Tool Helps Most
- Newsletter editors - check whether the issue hook is visible in the inbox.
- Lifecycle marketers - compare launch, onboarding, and winback subject lines before testing.
- Freelance writers - polish client campaign subject lines without needing an ESP preview.
Related guides
Frequently Asked Questions
- What does the Email Subject Line Tester check?
- It checks subject length, word count, mobile and desktop truncation, repeated punctuation, long all-caps phrases, emoji overuse, and common promotional trigger words.
- What is a good email subject line length?
- There is no single perfect length, but many teams aim for roughly 30-60 characters and put the most important hook in the first 40 characters for mobile inboxes.
- Should I write preview text with my subject line?
- Yes. Preview text gives you a second line of inbox copy and prevents email clients from pulling generic fallback text from the body.
- Does this guarantee higher open rates?
- No. Sender reputation, list quality, timing, audience fit, and offer strength also matter. This tool helps you catch copy and preview issues before sending.
- Is my subject line stored?
- No. The checker runs in your browser session only and does not store your subject or preview text.