SubMac / Free tools / Email subject line checker
Check your subject line before you hit send.
Type a subject line and get a score, an inbox preview and plain tips on length, spam words and clarity.
Runs in your browser. Nothing you type is uploaded.
How it looks in an inbox
How it works
Three steps. That’s it.
- 01
Type your subject
Paste the line you plan to send.
- 02
Read the checks
Length, spam words, capitals, punctuation and clarity, each with a tip.
- 03
Fix and copy
Edit until it scores well, then copy it.
Questions
Good to know.
What is a good subject line length?
About 25–60 characters, or 4–9 words. Phones show roughly the first 35–50 characters, so put the important words first.
What are spam-trigger words?
Words like “free”, “urgent”, “act now” or “guaranteed” that spam filters and busy readers associate with junk. One may be fine; several add up.
What subject should I use for a job application?
Keep it plain and specific: “Application: Marketing Assistant – Your Name”. If the job ad gives a reference number or tells you what to write, use that.
Does this use AI?
No. It follows clear rules, so the same subject always gets the same score, and nothing you type is sent anywhere.
Does a high score guarantee my email is opened?
No tool can promise that. The checks catch the common problems that hurt opens and deliverability.
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