Email Subject Line Tester

How to use the email subject line tester

1. Type or paste the subject line.
2. Read the previews to see what survives truncation in each client.
3. Act on the reader-facing notes; treat the spam wording as advisory.

About this tool

A subject line is not read; it is glanced at, in a list, usually on a phone, and usually truncated. This shows where the common clients cut it off — around 41 characters on an iPhone in portrait, about 47 on Gmail for Android, 60 in Outlook on the desktop — so you can see whether the part that survives still says anything.

That is the useful half of subject line advice, and it is measurable. The first forty characters carry the message; everything after them is a bonus for the minority reading on a wide screen.

The spam wording check is a heuristic and the page says so rather than dressing it up as a score. No filter has published its rules, and modern filtering weighs sender reputation, authentication and recipient engagement far above the words in a subject. A legitimate sender writing "free" is fine; a poor sender is not rescued by avoiding it. Any tool that returns a deliverability percentage from a subject line alone is inventing it.

The checks that are worth acting on are the ones about the reader rather than the filter: shouting in capitals, a stack of emoji that some clients render as boxes, repeated exclamation marks, and a false `Re:` on a first message — which is a dark pattern, and one recipients notice and remember.

Common uses

• Checking a subject line fits a phone's preview.
• Comparing two drafts of the same subject.
• Catching accidental shouting or a stray Re: before sending.

Frequently asked questions

How long should an email subject line be?

Around 40 characters survives everywhere, including an iPhone in portrait. Up to 60 is safe on desktop clients, and beyond that the end is decoration.

Do spam words really get emails filtered?

Far less than people think. Sender reputation, authentication and engagement dominate modern filtering, and no filter publishes its wording rules — so treat word lists as writing notes.

Should I use emoji in a subject line?

One can work for a consumer audience. Several read as insincere, and some clients still render them as empty boxes, which looks like a fault rather than a flourish.