Email Subject Line Tester
Test subject line length and preheader across major email clients. Gmail, Outlook, iOS Mail, Yahoo, Android, Apple Watch: on desktop and mobile. See exactly where each one truncates.
Email Marketing Intelligence
Subject-line truncation points differ by 20-40 characters between clients.
Gmail mobile cuts at ~35 characters. Outlook desktop shows ~60. iPhone portrait shows ~42. If the key hook sits past character 35, mobile Gmail users never see it. This tool previews across every major client so you can see what gets cut where.
Subject + preheader
Subject line 0 chars
Preheader (preview text) 0 chars
Preview across clients
Rules of thumb
35-character hook: Front-load the most important word in the first 35 characters. That's what mobile Gmail shows.
50-60 character sweet spot: Shows fully on most clients. Opens rate studies consistently show this range outperforms shorter and longer.
Preheader is the second line of selling: If the subject is a hook, the preheader is the confirmation. Don't waste it on "View in browser".
Avoid ALL CAPS and excessive punctuation. flagged by spam filters and feels pushy.
Next steps
Keep deliverability high so your subject lines even get seen
A great subject line is wasted if your emails land in Promotions. Check SPF, DMARC, DKIM, and spam-trigger words.
Frequently asked questions
What does this tool show?
Where major mail clients (Gmail, Outlook, iOS Mail, Yahoo, Apple Watch) truncate your subject line. And how it renders with preheader.
What subject line length works?
30 to 50 characters is the sweet spot. Longer gets truncated on mobile. Shorter can look empty.
What is the preheader text?
The preview text after the subject. 40 to 90 characters. Often more important than subject for mobile open rates.
Should I use emojis?
Occasionally yes: can lift open rates. Overused they look like spam. One emoji per subject max.
Can emojis break on older clients?
Some older desktop clients render them as boxes. Modern clients handle them fine.
Does CAPITALS hurt deliverability?
All-caps subjects get flagged by some spam filters. Partial caps (one word) is fine.
Should I personalise subjects?
First name in subject can lift open rates 10 to 25%. Overuse makes it feel templated.
What about question-form subjects?
Work well for engagement emails. Mix with declarative subjects: all questions reads formulaic.
Does Gmail truncate differently than Outlook?
Gmail: ~70 characters on mobile. Outlook desktop: ~90. iOS Mail: 35 to 70. The tool shows each.
What about Apple Watch?
Severely limited: ~20 characters. For transactional emails this matters.
Should I include the brand name in subject?
From-name shows the sender; subject can skip the brand. Front-loading brand uses expensive subject real estate.
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