How to use the Email Subject Line Tester
- 1
Paste your subject line, and the preheader if you use one.
- 2
Check the inbox preview and fix anything flagged.
- 3
Test two versions with your email platform's A/B feature and keep the winner.
What the score checks
The score combines checks that consistently affect opens: length and mobile cut-off, spam-trigger words, all caps and excess punctuation, emoji overuse, and signs of a clear, specific benefit such as a number or a question.
Write for the preview
On phones, roughly the first 30 to 40 characters show. Put the specific benefit first, and use the preheader for the supporting detail instead of repeating the subject.
- Lead with the outcome or the news
- Be specific: numbers beat adjectives
- Avoid fake urgency and "RE:" tricks
- Match the subject to what the email delivers
Frequently asked questions
What is the ideal subject line length?
Around 30 to 50 characters works well across devices. What matters most is that the first 30 characters make sense on their own.
Do spam words really hurt?
Modern filters look at sender reputation and engagement more than single words, but heavy hype language still lowers trust and opens.
Should I use emoji?
One relevant emoji can help stand out. Several look spammy, and they don't render the same everywhere.
Is my text stored?
No. Everything runs in your browser.