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Cold email subject line tester: score your subject before you send

Type a cold email subject line and get a score out of 10 against the rules Pipefire writes its own subjects to: length, case, sales language, and whether it gives the pitch away. Free, no sign-up, nothing stored.

What does this cold email subject line tester check?

  • Length: at most 4 words and 40 characters. Three large cold email datasets agree that short subjects get opened most.
  • Case: lower case, except names. Capitalised subjects read like a campaign.
  • The pitch: no words that name what you sell, such as "website", "SEO" or "platform". The subject earns the open; the body makes the case.
  • Sales language: no "free", "guaranteed", "act now" or exclamation marks, and no fake "Re:".

What makes a good cold email subject line?

One that looks like a note from one person to another and names something in the reader's world: "quiet tuesdays" for a salon, "storm damage" for a property manager. It should make sense to them before they open it and say nothing about your product. Our guide to cold email subject lines has examples by situation.

Should a cold email subject line be a question or use numbers?

The research disagrees, so the tester notes them rather than marking them down. One large study found question subjects opened best; two others found they cost opens. Test both on your own list. A question usually works better as the last line of the email, where it asks for the reply.

Does a good subject line stop a cold email going to spam?

Barely. Spam filters weigh the sending domain's reputation and authentication far more than the words. A clean subject from a domain with no SPF, DKIM or DMARC still lands in spam. Check those with the domain checker, and see why cold emails go to spam.