Email Subject Line Tester
Score your email subject line for length, spam-trigger words, caps, punctuation and engagement signals, with a live inbox preview.
Last reviewed by the Radiatus Cloud team
Scoring checks length, word count, spam-trigger words, ALL CAPS, excessive punctuation, personalization, numbers and urgency. Heuristics based on common email-marketing guidance — always A/B test with your real audience.
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Score an email subject line
A subject line decides whether an email is opened, and small issues, length, spam words, too many caps, hurt it. This tool scores your subject line for length, spam-trigger words, capitalisation and punctuation, so you can improve it before sending.
Why the subject line is everything
The subject line is the entire pitch for whether an email gets opened, and several avoidable factors undermine it: a line too long is truncated on mobile, spam-trigger words push it toward the junk folder, excessive capitals or exclamation marks read as shouting or spam, and cluttered punctuation looks unprofessional. Scoring the subject against these factors surfaces the specific problems to fix, which is far more useful than guessing why open rates are low. It is a quick check that catches the issues quietly costing you opens.
A quick quality check
It runs entirely in your browser, so nothing you enter is uploaded, which matters when the input concerns your own business or security posture.
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Frequently Asked Questions
Why does the subject line matter so much?
Because it is the entire pitch for whether an email is opened. A weak subject line means the email is never read, however good its content.
What hurts a subject line?
Being too long (truncated on mobile), spam-trigger words, excessive capitals or exclamation marks, and cluttered punctuation, all of which the tool checks.
How does subject length affect opens?
A line too long is cut off on mobile, where most email is read, so the key message may never be seen. Concise subjects fare better.
What are spam-trigger words?
Words associated with spam that can push an email toward the junk folder. Avoiding them helps the email reach the inbox to be opened.
Is my input uploaded?
No. The tool runs entirely in your browser.
Privacy & Security
Runs entirely in your browser. No data is sent to any server.
How to Use
Type your subject line to get an instant score out of 100 with specific fixes and a preview of how it truncates on mobile.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
Related Tools
Incident Impact Calculator
BusinessEstimate the cost of a security incident from severity, affected users and downtime hours, with a compliance and trust rating and the response actions each severity level demands.
Third-Party Risk Assessor
BusinessAssess vendor risk based on data access and type.
Data Breach Cost Estimator
BusinessEstimate what a data breach would cost from records exposed, cost per record, days to detect and hours of downtime, split into direct and indirect costs.