Marketing · Free Tool
Email Subject Line Tester
Preview how your subject line and preheader look in Gmail and Apple Mail, check them against real client truncation points, and scan for common spam-trigger words.
Subject length vs. client cutoffs
Gmail — inbox row
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Apple Mail / iOS — inbox row
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Spam-trigger word check
No common spam-trigger words found in the subject line.
Heuristic keyword check only — not a real spam-filter score. Spam filters weigh sender reputation, authentication (SPF/DKIM/DMARC), engagement history, and full message content far more heavily than any single word here.
About this tool
The subject line and preheader are the only parts of an email most recipients ever see before deciding whether to open it, yet they are frequently written last and tested least. This tool renders live inbox-row mockups styled after Gmail and Apple Mail / iOS so you can see, character by character, exactly where each client cuts off your text and how the preheader reads once it is squeezed in alongside the subject.
It also checks your subject line against character-count thresholds for Gmail on mobile and desktop, Outlook desktop, and Apple Mail on iOS — each client truncates at a different point, so copy that looks complete in one inbox can be cut off mid-word in another. A bundled list of common spam-trigger words and phrases flags terms worth a second look, though this is a simple keyword heuristic, not a real spam-filter score; sender reputation, authentication, and engagement history matter far more than any single word.
Common uses
- Checking whether a subject line will get truncated before the key offer or call-to-action on mobile Gmail before scheduling a campaign send
- Drafting preheader text that complements a subject line instead of repeating it, and confirming both fit together cleanly in an inbox preview
- Running a quick sanity check on subject line wording for common spam-trigger phrases before sending to a large list
Frequently asked questions
Are the character limits exact for every email client?
No — inbox clients render subject lines based on pixel width, font, screen size, and zoom level, not a fixed character count, so the limits shown here (roughly 30-40 characters for Gmail mobile, 60-70 for Gmail desktop, ~60 for Outlook desktop, and ~90 for Apple Mail on iOS) are practical approximations based on common real-world behavior, not guaranteed cutoffs.
Does flagging a spam-trigger word mean my email will go to spam?
No. This is a basic keyword match against a list of commonly cited spam-trigger words and phrases, meant as a quick heuristic prompt to reconsider your wording. Real spam filters weigh sender reputation, domain authentication (SPF/DKIM/DMARC), recipient engagement history, and full message content far more heavily than any single word in a subject line.
Is my subject line or preheader text sent anywhere?
No — everything runs client-side in your browser. The subject line, preheader, and any matches against the spam-word list are computed locally in JavaScript and never transmitted to a server.
Is my data uploaded to a server?
No. This tool runs entirely in your browser using JavaScript — nothing you type is transmitted, logged, or stored anywhere. You can even use it offline once the page has loaded.