Subject Line Spam Checker

About Subject Line Spam Checker

A subject line has an outsized effect on whether a marketing or outreach email even gets opened — but it's also the single biggest factor spam filters weigh when deciding whether an email lands in the inbox or gets routed to junk. Certain words and patterns ("free," "act now," excessive exclamation marks, ALL CAPS) are strongly correlated with spam in filter training data, regardless of how legitimate the actual email is.

This tool scores a subject line against several concrete signals: overall length (subject lines over 60 characters often get truncated in inbox previews, especially on mobile), the presence of common spam-trigger words and phrases, the number of all-caps words, excessive exclamation marks, and emoji usage. Each issue reduces the score from a starting 100, giving you a quick numeric read on deliverability risk.

This checks structural, well-documented spam-filter signals — it doesn't guarantee inbox placement, since actual spam filtering also considers sender reputation, domain authentication (SPF/DKIM/DMARC), and recipient engagement history, none of which a subject-line checker can evaluate. Use this as a quick sanity check before sending, not a guarantee of deliverability.

How it works

1. Enter your subject line. Type the exact subject line you're planning to send.
2. Review the score and flags. See a 0-100 score with specific issues called out.
3. Revise and re-check. Adjust the subject line and watch the score update instantly.