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Email subject line checker

Check subject lines for length, mobile/desktop truncation and spam trigger words.

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Output
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Email subject line checker
Paste one or more email subject lines, one per line, and this tool scores each one for deliverability risk before you hit send. For every subject it reports the character count, whether it survives the truncation point of a typical mobile inbox and a typical desktop client, and which words trip common spam filters — so you can fix a line before an A/B test wastes a send.
Set separate character limits for mobile and desktop, since most mail apps clip a subject line well before the 78-character convention email itself allows for. The truncation preview shows exactly what gets cut, not just a fits/doesn't-fit verdict. Toggle warnings for ALL CAPS words, excessive punctuation ("Buy now!!!") and a high emoji count — all three read as promotional to spam filters and to recipients scanning an inbox. The spam-word list is selectable by language, because "free" and "zadarmo" trigger different filters. Turn on preheader checking to also test the preview text mail clients show next to the subject — write a line as Subject|Preheader text and both halves get checked and counted separately.
Paste several subjects at once to compare a batch from a campaign draft or an A/B test. With sorting on, the riskiest subject line moves to the top of the report so the one that needs fixing first is the one you see first; turn it off to keep your original order instead.
Everything runs in your browser. Subject lines and preheader text are never uploaded anywhere, so it is safe to check drafts before a campaign goes out. Copy the report, download it as a .txt file, or send the output back into the input to refine a subject and re-check it.
FAQ
What counts as a spam trigger word?
A curated list of words and phrases (like "free", "act now" or "guaranteed") that commonly lower deliverability or read as promotional to spam filters. Pick the list language that matches your subject line.
Why does mobile truncate a subject shorter than desktop?
Phone inboxes show a narrower subject column than desktop mail clients, so they typically clip a line sooner. Set your own mobile and desktop limits if your audience skews toward a specific client.
How do I check a preheader line?
Turn on "Check preheader" and write the line as Subject|Preheader text — everything after the first | is treated as the preheader and counted and scanned separately.
What does the risk score mean?
Each spam trigger, ALL CAPS word, run of punctuation, high emoji count and truncated line adds to a subject's score. Low is 0, medium is 1–3, high is 4 or more — sort by risk to see the riskiest subject first.
Are my subject lines uploaded anywhere?
No. Subject and preheader checking runs entirely in your browser — nothing you paste here is sent to a server.