Email writing
Free Email Subject Line Tester
Paste a subject line and instantly see how it truncates on desktop and mobile Gmail, plus common issues that hurt open rates.
Updated September 6, 2026 · Free · Runs in your browser
An email subject line tester shows how a subject will look in a typical Gmail desktop and mobile inbox list, and flags length, all-caps words, stacked punctuation, and filler openers before you send.
0 characters · runs in your browser, nothing is sent or stored
How to test an email subject line
- Paste the subject. Type or paste your subject line into the tester. Nothing is sent to a server.
- Read the inbox preview. Check the desktop (~65 characters) and mobile (~38 characters) previews to see what gets cut.
- Fix flagged checks. Front-load the point, stay under about 60 characters, drop all-caps, stacked punctuation, extra emoji, and filler openers like “quick question”.
- Copy it into Gmail. Use the revised subject when you compose in Gmail.
What this tool is not
- It does not send email or change anything in Gmail.
- It does not predict or guarantee open rates.
- Truncation is approximate — real devices and fonts vary.
Frequently asked questions
Is this subject line tester free?
Yes — it runs entirely in your browser, requires no signup, and nothing you type is sent to a server or stored.
What does the tester check?
Character count against typical desktop (~60–70) and mobile (~30–40) display limits, all-caps words, stacked punctuation, emoji count, and filler openers like “quick question” that waste visible characters.
What is the ideal subject line length?
Keep the essential part within the first 40 characters so it survives mobile truncation, and stay under roughly 60 characters overall.
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