How it works
- Type or paste one subject line.
- The page counts characters and words, and marks merge tokens such as {{first_name}}.
- A preview shows roughly where a narrow phone inbox may cut the line. Mail apps differ.
Questions
What does the mobile cutoff mean?
The preview fades the subject after about 40 characters. That is an approximate width for a narrow inbox, not a measurement of Gmail, Apple Mail or Outlook.
Is there a required subject length?
No. This page does not treat a character count as a passing score. It shows the length so you can see what may be hidden.
Which tokens does it recognise?
It flags brace, bracket and percent placeholders such as {{company}}, {first_name} and %FIRSTNAME%. It does not check that your sending tool will replace them.
Does a short subject avoid spam filters?
No. Length and the word list are editing aids. They do not describe a mailbox provider’s filter.
Is the subject sent anywhere?
No. The tester runs locally in the browser.