Subject line tester
See how your subject line looks in the inbox, and catch what could hurt opens before you send.
Checks as you type. Tags like {{first_name}} are filled in with sample values for the preview.
What makes a good cold email subject line
Cold email subject lines work differently from newsletter ones. The best read like a note from a colleague: short, lowercase or sentence case, specific to the reader, and with nothing that looks like an ad.
Keep it under about 40 characters so it shows in full on a phone, leave out exclamation marks, caps and sales words, and never fake a reply with Re:. Then test two versions and keep the one that gets more replies.
How to use it
- 1
Type your subject line. Use tags like {{company}} if you personalize. We fill them in for the preview.
- 2
Add preview text. Optional: the first line of your email, which shows next to the subject.
- 3
Fix what’s flagged. Each check says why it matters. The score updates as you type.
Questions about subject lines
How long should a cold email subject line be?
Under about 40 characters, often just two to five words. Phones cut subjects off around there, and short subjects look more personal.
Should I use the person’s name in the subject?
It can help, but their company or a specific detail usually works better than a first name, which many sales emails now use.
Do emoji help open rates?
In newsletters, sometimes. In cold email they make the message look automated, so leave them out.
Is it OK to start a subject with Re:?
No. Faking a reply might get one extra open, but people notice, it damages trust, and inbox providers treat it as deceptive.
How is the score worked out?
It starts at 100 and loses points for each check that flags something: more for serious issues like a fake Re: or several spam words, less for small ones. It’s a guide, not a prediction. The real test is replies.
Setup checks out? Start sending.
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