Email subject line tester

Type your subject line and, if you have one, the preview text that inboxes show next to it. The tester runs a short checklist on five things: is it clear what the email is about, does it give a reason to open, does it fit a phone inbox with the point up front, does it avoid the patterns spam filters and readers distrust, and does the preview text add something new.

Each line is a yes/no check and the score updates as you type, so you can try a variant and watch which checks turn green.

People decide whether to open from the sender name and a handful of words. "Your March invoice + 2 features you asked for" tells them exactly what's inside and why it matters to them. "Exciting news!" could be anything, so it reads as marketing and gets skipped. A specific detail, such as a name, a number, a date or a topic, does most of the work.

Most email is opened on a phone, where only the first few words of a subject line show before it is cut off. Put the point first, cut throat-clearing like "Just wanted to let you know", and keep it to a short phrase. If something important sits at the end of a long subject line, assume nobody sees it.

ALL CAPS, runs of exclamation marks, $$$ and phrases like "act now" or "you've won" look like spam to filters and to people. A fake "Re:" or "Fwd:" might lift one send, but it burns trust, and in the US the CAN-SPAM Act forbids subject lines that mislead about the content of the message.

The preview text (also called preheader) is the grey line most inboxes show after the subject. Left empty, the inbox fills it with whatever comes first in the email, often "View in browser" or an unsubscribe line. Use it to add a second reason to open rather than repeating the subject.