Free tool
Test your subject line before you send it.
Type a subject line to get a score and the reasons behind it, plus roughly how it looks on a phone.
The short answer
A good cold email subject line is short, specific and sounds like one person writing to another. Under about 40 characters means it should show in full on most phones. Avoid capitals, exclamation marks, discount language and fake "Re:" prefixes, which win an open and lose the reader's trust.
How the score works
It starts at 100 and takes points off for what makes a subject look like marketing: length, risky phrases, capitals, exclamation marks, fake replies and emoji. Each check is shown, so you can see why you got the score.
These are rules of thumb, not a prediction. No tool can tell you your open rate, and a subject that scores well can still fail if it isn't relevant to the reader. The real test is sending two versions and comparing replies.
Ideas that tend to work
- Name something about them: their company, role, or something they posted.
- Write it in lower-key words, like an email to a colleague.
- Make it match the email. A clever subject that misleads only gets you a spam complaint.
More ideas in our cold email subject lines.
Questions
How long should a cold email subject line be?
Short enough to show on a phone, which is usually about 35 to 40 characters. Many good ones are two to five words.
Should I use Re: in a cold email?
No. It pretends you've spoken before, and it breaks trust as soon as someone opens it.
Do emoji help?
They're common in marketing emails, so they can make a one-to-one email look like a campaign. For cold email, leave them out.
Can this predict my open rate?
No. It checks for common problems. Open rates are also less reliable than they used to be, so judge a subject by the replies it gets.
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