Free browser tool
Email Subject Line Checker
Check an email subject line for length bands, audience fit, clarity, preview repetition, priority action, send actions, timing signals, send-window choice, inbox QA, before-and-after fixes, mobile preview, send packet, body opener, copy, and clear controls.
Updated 2026-07-06
Result summary
Ready to check an email subject line.
Score appears after the check.
Mobile inbox preview appears after the check.
Send decision appears after the check.
Audience fit appears after the check.
First body sentence suggestion appears after the check.
- Action
- -
- Timing
- -
- Preview
- -
- Reply prefix
- -
Send risk
-
Run the check to see whether the subject is ready, risky, or missing key inbox signals.
Send actions
Priority action appears after the check.
Final send checklist
Preview advice
Inbox QA
Best pattern appears after the check.
Length bands
- Desktop
- -
- Mobile
- -
- Preview
- -
Send window cues
Send window choice appears after the check.
Subject options
Before and after fix
- Before
- -
- After subject
- -
- After preview
- -
- Why
- -
How to use this tool
- Paste or type your input into the tool.
- Choose the action or option that matches your task.
- Review the output before copying it into another app.
Notes
Review subject length bands, audience fit, preview repetition, the next priority action, copyable send actions, action and timing signals, send-window choice, inbox QA checklist, best subject pattern, final send checklist, mobile preview, send packet, body opener, rewrites, and privacy cautions.
Inputs are processed in the browser for this static MVP. Avoid pasting secrets into any online tool unless you understand the environment.
FAQ
What makes an email subject line clear?
A clear subject names the topic and gives one useful signal about action, timing, or status. A busy reader should know what the message is before opening it.
How long should it be?
Shorter is usually easier to scan, but the best length depends on whether the action and topic are visible. Long setup words belong in preview text or the body.
Should preview text repeat the subject?
No. Preview text should add context, timing, attachment detail, or a decision request, not duplicate the subject line.
Why enter sensitive terms?
Use the field for account names, addresses, private project labels, or anything that should not appear in the inbox scan line. The check flags those words so you can move details into the body.
What are send-window cues?
They are visible timing words such as today, Friday, or next week. The tool surfaces them so the subject, preview, and first body sentence can repeat the same real deadline.