Score your subject line out of 100, catch spam triggers before you hit send, and see exactly how it renders in a real inbox on mobile and desktop.
Score your subject line out of 100, catch spam triggers before you hit send, and see exactly how it renders in a real inbox on mobile and desktop.
Over half of email opens happen on mobile, where subject lines truncate around 35 to 40 characters. If your key message lands after that point, most recipients never see it.
All scoring happens locally in your browser using established email marketing benchmarks, not a live spam filter test. A flagged word rarely sends an email to spam on its own, deliverability depends on many factors including sender reputation and authentication that this tool cannot check.
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Your subject line decides whether an email is opened, ignored or sent to spam. It is the highest-leverage line of copy in any email campaign.
This free email subject line tester scores your subject line, checks length, flags spam trigger words, excessive capitals and punctuation, and shows an inbox preview so you can see how it will look before you hit send.
Test several versions in a minute, then send the strongest two as an A/B test.
A strong subject line is usually 30 to 50 characters, specific, free of spam triggers like "100% free" or "ACT NOW", and paired with a preheader that adds information. Type yours above to get a score and inbox preview.
Write two or three options before testing. Comparing is faster than perfecting one.
Add emoji or personalisation tokens exactly as they will be sent.
Trigger words, ALL CAPS and heavy punctuation are highlighted so you can fix them.
See the overall rating and how your length compares with what inboxes display.
Check the inbox preview, then edit until it reads well and nothing important is cut off.
The score combines the factors most linked to opens and inbox placement.
Top: all caps, three exclamation marks and spam phrases. Bottom: specific, urgent and easy to trust.
Length 30 to 50 characters is the sweet spot
Spam triggers "free!!!", "guaranteed", "act now"
Capitals avoid ALL CAPS words
Punctuation max one ! or ?
Clarity specific benefit or curiosityNo tool can guarantee inbox placement. Sender reputation and list quality matter more than any single word.
Rewriting a promotional subject line.
Inboxes cut long subject lines. Put the key words first.
| Where it is read | Characters visible (approx.) | Tip |
|---|---|---|
| Mobile inbox | 30 to 40 | Front-load the benefit |
| Desktop Gmail | 60 to 70 | Use the preheader for detail |
| Desktop Outlook | 50 to 60 | Keep it under 50 to be safe |
| Smartwatch and notifications | 20 to 25 | First three words must make sense alone |
Relevance beats tricks. Readers open emails that clearly matter to them.
About 30 to 50 characters works well across devices. Mobile inboxes often show only 30 to 40 characters.
Phrases like "100% free", "act now", "guaranteed", "cash" and "winner", especially with all caps and lots of exclamation marks. Modern filters weigh sender reputation more than single words.
One relevant emoji can help a subject line stand out. Test it with your audience and check it renders on major email clients.
The short preview text shown after the subject line in most inboxes. Use it to add detail or a second reason to open.
Often, when it is relevant. Using a first name helps less than referencing something the reader actually did or wants.
Open rates vary widely by industry and are less reliable since Apple Mail Privacy Protection. Track clicks and conversions too.
We design, write and automate email flows that turn subscribers into repeat customers. Explore our digital marketing services.