Cold emailsubject line tester.
Score a subject line for length, sales words and tone, and see exactly how much of it shows in Gmail, Apple Mail and Outlook.
How it works
- Type a subject lineMerge tags are fine
- See the scoreWith what to change
- Check the previewsPhone and desktop
Free, no sign-up. Runs in your browser. Nothing you type is sent anywhere.
The tool
Your subject line
How it shows in the inbox
What works for cold email
- Two to five words that look like an internal email.
- lowercase reads more human than Title Case.
- Mention something specific to them: their company, role or city.
- Never a fake Re: or Fwd:.
What makes a cold subject line work.
What the result means, and how to fix what it finds.
Short and plain
The best cold subject lines look like an email from a colleague: two to five words, often lowercase, with nothing that sounds like marketing. 'quick question' and 'idea for {{company}}' outperform clever lines because they don't trigger the 'this is a sales email' reaction.
Phones cut it short
Most email is read on a phone, where only the first 35 to 40 characters show. Anything past that is cut. Put the meaningful part first, and check the previews to see exactly what your reader sees.
What to avoid
Sales words (free, offer, discount), capitals, exclamation marks and emoji all make a subject line look like advertising. A fake 'Re:' or 'Fwd:' tricks people into opening, then annoys them into reporting you, and Gmail flags such subject lines.
Make it about them
A subject that mentions their company, role, city or something they did gets opened more than one about you. Use merge tags carefully: an empty field leaves a gap, so check your list has the data, and test it with our merge tag preview.
Test them properly
One subject line beating another on a few dozen sends usually means nothing: the difference is often chance. Test two at a time, send each to at least a few hundred people from the same list, and compare replies, not just opens. Opens are less reliable than they used to be, because Apple Mail and some security tools open emails automatically. Change only the subject between the two versions, so you know what made the difference. Keep the winner, then test it against a new idea. Write down each result, so the next campaign starts from what your audience responded to rather than from scratch. Over a few months you'll learn which kinds of subject line your buyers answer, which is worth more than any list of examples. And test the email body too: a great subject on a weak email only gets more people to ignore it.
In mailzy
Test subject lines on real sends.
mailzy campaigns let you A/B test versions of each email and show which one gets more replies.
Questions before you start.
Ask us on the chat if yours isn't here. A real person answers.
Should cold email subject lines be lowercase?
It often helps: lowercase reads like a quick personal note. It isn't a rule, but Title Case reads like a newsletter.
How long should a subject line be?
Under 40 characters so it shows in full on phones; two to five words is ideal for cold email.
Do emoji help?
Not in cold email. They make it look like marketing.
More free tools.
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Open the toolEverything for cold email, in one place.
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