Tool · 3 free checks
Cold Email Subject Line Checker
Paste a subject line to see whether it reads fully on a phone, trips spam filters or sounds like an advert — with a score and specific fixes.
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See it in 30 seconds
What makes a cold email subject line work
The best cold email subject lines are short, specific and calm. They mention the reader's business or a real problem, read fully on a phone, and avoid words that spam filters and busy owners associate with adverts — "free", "guaranteed", "act now", prices and exclamation marks.
What the checker looks at
- Length — phones show roughly the first 35–45 characters.
- Spam-trigger words — a list of words and phrases that commonly hurt delivery or replies.
- Shouting — ALL-CAPS words and exclamation marks.
- Honesty — fake "Re:" or "Fwd:" prefixes, which also break the US CAN-SPAM rules.
- Personalisation — whether it speaks to the reader or their business.
Frequently asked questions
Is a high score a guarantee of opens?
No — it means the subject avoids the common mistakes. Opens also depend on your sender name, sending reputation and who you're writing to.
How long should a subject line be?
Aim for 25–50 characters and 3–8 words, so it shows in full on most phones.
Is it free?
3 checks free with no sign-up; unlimited with ClientoraHQ Tools Pro.