Email subject line length checker

A subject line is cut around 60 characters on desktop and around 35 on mobile — and mobile is where most email is opened. Front-load accordingly.

Thirty-five characters is roughly five words, which is far less room than people assume when writing at a desk. The preview text beside it is the underused half: most clients show 40 to 90 characters of the email body after the subject, and leaving that to be filled by "View this email in your browser" wastes the most valuable line in the inbox. Set it deliberately with a preheader. Two things to avoid regardless of length: ALL CAPS and multiple exclamation marks both correlate with spam filtering, and the RE: or FW: prefix on a message that is neither is a trust cost that outweighs any open-rate gain.