Subject line tester
Check a newsletter subject line and preview text for length, phone truncation, spam-trigger phrases, shouting and misleading tricks. Instant, free, and private: it runs in your browser.
Try an example:
Checking
This scores wording only. Inbox placement is decided mostly by authentication and sender reputation. For that side, read this email deliverability guide.
What the tester checks
- Length and truncation. Character count, with a live phone and desktop inbox preview so you can see where your line gets cut.
- Trigger phrases. A list of phrases common in spam and scams ("free gift", "act now", "you've been selected"), split into strong and mild. Strong ones cost more points.
- Shouting. All-caps words (common acronyms like AI or SEO are ignored), stacked punctuation and emoji overload.
- Misleading tricks. Fake "Re:" or "Fwd:" prefixes, which also run against US CAN-SPAM rules on deceptive subject lines.
- Preview text. Whether you wrote one, whether it repeats the subject, and whether its length suits most inboxes.
- Merge tags. Personalization tags that need a fallback so nobody sees a blank.
The score starts at 100 and loses points for each problem, weighted by how much it tends to matter. It is a writing aid, not a prediction of open rate. To check the technical side (SPF, DKIM, DMARC), use our email deliverability checker. For the full craft, read our guide to newsletter subject lines, and for what goes under the subject line, how to write a newsletter.
FAQ
Does this test tell me if my email will land in spam?
No. It checks the words in your subject line and preview text. Whether a message reaches the inbox depends mostly on authentication (SPF, DKIM, DMARC), your sending reputation and how readers engage. Use this to catch obvious problems, then test real sends with a seed or placement tool.
How long should a newsletter subject line be?
Short enough that the important words show on a phone. Phones often cut subject lines somewhere around 30 to 45 characters depending on the app and screen, so put the key idea first and keep most lines under 60 characters.
Are spam trigger words still a thing?
Less than they used to be. Modern filters weigh reputation and engagement far more than individual words. But phrases like "free gift" or "act now" still look like spam to people, and people deciding not to open is what hurts reputation over time.
Is my subject line sent anywhere?
No. The checks run entirely in your browser with JavaScript. Nothing you type is stored or sent to a server.