Email Subject Line Tester
Nearly half of recipients decide to open on the subject line alone, and spam filters read it first. Paste yours below for an instant score on length, spam-trigger words, formatting, emoji, personalization and specificity, with concrete fixes for anything dragging it down.
Free, no signup, nothing stored. The interactive tool loads with JavaScript; the scoring rules it uses are described below.
What the email subject line tester checks
- Length against the 30-60 character sweet spot and the ~45 character mobile preview cutoff
- More than 100 spam-trigger phrases, weighted by severity the way filters treat them
- ALL-CAPS words, exclamation runs and other formatting that shouts
- Emoji count: one can lift opens, four or more look like spam
- Personalization tokens ({first_name}) and bracket tags like [Webinar]
- Power words and numbers that make the promise concrete
How to use it
- Write or paste your subject line. Type the subject line exactly as you plan to send it, including any merge tags like {first_name} or bracket tags like [Webinar].
- Read the score and the breakdown. The tester scores nine signals out of 100 and flags every spam-trigger phrase it finds, weighted by how hard filters punish it.
- Apply the fixes and rescore. Work through the suggestions, retest, and aim for 70 or above before the campaign goes out.
Frequently asked questions
What is a good subject line score?
70 or above. Above 85 the subject is genuinely strong: right length, no spam triggers, a power word or number, and clean formatting. Anything under 40 carries real deliverability or open-rate risk.
Which words trigger email spam filters?
The heavy hitters are income claims ("make money", "extra income"), pressure ("act now", "limited time offer"), finance ("risk free", "no obligation", "guaranteed") and pharma terms. One mild phrase like "free" rarely sinks you on its own, but two or three stacked together with ALL CAPS and exclamation marks will. This tester weighs each phrase by severity.
How long should an email subject line be?
30-60 characters, or about 3-9 words. Most phone inboxes cut the preview at roughly 45 characters, so put the important words first.
Do emojis in subject lines help or hurt?
One relevant emoji can lift opens, especially on consumer lists. Four or more correlate with spam complaints and look unprofessional in B2B inboxes. Test with your own audience; this tool penalizes heavy emoji use.
Is my subject line stored anywhere?
No. Scoring runs in your browser and over a rate-limited endpoint that writes nothing to a database. We never see or store what you test.
Want this inside your marketing platform?
The tools on this page run on the same rules and benchmarks Medivot applies to your campaigns, webinars and pages. Scores in context, next to the work itself.
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