What it does

The subject line you wrote is not the one your reader sees. Each inbox cuts it at a different length, and the preview text next to it is often missing or a repeat.

Subject line tester shows you exactly what each inbox shows, checks for the things that quietly cost opens, and writes three rewrites that fit a phone screen in full.

How it works

  1. Type the subject line and preview text you are about to send.
  2. You see what Gmail on a laptop and a phone, Outlook on Windows and a phone, and Apple Mail on an iPhone each show, with the cut-off words marked.
  3. We check for a subject cut off on mobile, missing preview text, a preview that repeats the subject, shouting capitals, and a merge tag that did not fill.
  4. You get three rewrites, each on a different angle, that fit the phone screen in full.

Getting the most from it

  • Always write preview text. Without it the inbox shows whatever text comes first in your email.
  • Put the words that matter in the first 30 or so characters. That is what survives on a phone.