Subject line tester
Paste a subject line to get an instant readability and spam-risk score. The checks are structural — length, caps, punctuation, trigger words — so they help in any language.
What the score checks
A good subject line is short enough to show in full on mobile, specific, and free of the patterns spam filters distrust. The tester scores the structural signals you can control before sending.
- Length — long subjects get truncated, especially on phones
- Word count — a tight, scannable line beats a sentence
- Spam-trigger words — 'free', 'act now', '$$$' and friends raise risk
- ALL-CAPS and excess punctuation — classic spam-filter red flags
- Emoji and personalization — used well, both can lift opens
Writing subject lines that get opened
- Lead with the value or curiosity, not your brand name
- Keep it under about 60 characters so nothing gets cut
- Match the subject to the content — misleading lines kill trust
- Test one variable at a time so you learn what actually moves opens
Frequently asked questions
Does a high score guarantee inbox placement?
No. The subject is one signal; deliverability also depends on authentication, sender reputation and engagement. A clean subject helps, but it's not the whole story.
Do the checks work in other languages?
The structural checks — length, caps, punctuation, personalization — work in any language. The spam-word list is English-focused, so weight that check accordingly.
Should I always use emoji?
Not always. Emoji can lift opens for some audiences and annoy others. Test with your own list rather than following a blanket rule.
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