Free email subject line tester

Between 30 and 50 characters. Gmail on a phone shows roughly 35 to 40 before it cuts, and Outlook's desktop list is similar, so put the words that matter first and treat anything past 50 as a bonus the reader may never see.

Specificity. A name, a number, a date or a decision beats a clever line almost every time. The reader is scanning a list and deciding whether this concerns them; a subject that answers that in four words wins.

Modern filters score the whole message and the sender's reputation, not a banned word list, so one word rarely sends you to spam on its own. Stacking them does: all caps, several exclamation marks, "free," "guaranteed," "act now" and a currency figure in one line is a pattern filters recognise.

The role and your name: "Senior Analyst application, Priya Raman". Recruiters filter and sort by subject, so anything that helps them find you again later is worth more than anything clever.

In consumer newsletters they can lift opens slightly. In cold outreach, job applications and anything internal, they cost you credibility and can render as a box on older clients. If in doubt, leave them out.