Email subject tester
Score an email subject line with local rules only: character and word counts, spam-word hits, uppercase ratio, exclamation marks and emoji, plus Gmail and Outlook truncation previews and concrete suggestions.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Subject line
Everything is analysed locally with rules — no network calls and no AI. The score is a relative hint; real inbox placement also depends on your sending domain and engagement history.
Result
Type a subject line to see the score and truncation previews.
What this tool does
- Sanity-check a marketing subject before sending: swap out words like FREE, 100% or limited time to cut the odds of landing in spam.
- Check mobile truncation: phone inboxes show roughly 40 characters, so keep the subject under 50 and front-load the key information.
- Review internal announcements for all-caps runs and stacked exclamation marks — both trip spam filters and read like shouting to colleagues.
- Prepare a few A/B variants, screen out the obviously weak ones with the score, and send the rest.
Example
Input
Quarterly product roadmap review for the platform team
Output
54 characters (over the 50-character mobile guideline), 8 words, 2.2% uppercase, 0 exclamation marks, 0 emoji, no spam rules matched; score 92 (excellent). Gmail mobile truncates at 40 characters, while Gmail desktop and Outlook show it in full.
Shorten it to "Q4 platform roadmap review" and the count drops to 27 characters, so every client shows it in full — and the score stays perfect.
Frequently asked questions
How is the score calculated?
It starts at 100: spam-word weights subtract up to 40, an uppercase ratio above 30% costs 10 (above 50% costs 20), more than one exclamation mark costs 8 (more than three costs 15), a subject over 50 characters costs 8 (over 70 costs 15), and more than three emoji costs 5. Anything at 85 or above is "excellent".
Why 50 characters for mobile?
Phone inbox lists fit roughly 40 characters, while Gmail desktop shows about 70 and Outlook about 60. Keeping the subject within 50 characters is a safe rule of thumb, and the tool shows truncation previews for all three widths.
What is in the spam-word list?
Two self-built rule sets: English entries such as FREE, 100%, guaranteed, act now, click here, winner and urgent, plus Chinese entries such as 免费, 限时, 秒杀, 中奖, 立即购买 and 最低价. English rules match on word boundaries, so "Freedom" does not trigger "free".
Does the analysis go online or upload my subject?
No. It is all local regex and counting in the browser — no requests, no AI service, and the input disappears when you refresh.
Why did a perfectly fine subject score low?
The rules only see the subject text, not your sending domain, recipient engagement, body content or links, so treat the score as a relative hint rather than a hard standard.
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