Email Subject Line Tester
Score your subject line on length, spam triggers, caps, and personalization to predict open rate.
Runs entirely in your browser. Your subject line is never uploaded anywhere.
How to use this tool
Type or paste your email subject line into the box and press Test subject line. This free email subject line tester instantly checks the character length, scans for common spam trigger words, measures caps and emoji overuse, and looks for personalization. You get a single subject line score from 0 to 100, an open rate grade, a breakdown of each check, and plain tips you can act on right away. Adjust your wording and test again until the score is where you want it.
How the score works
Length out of the 30-50 character sweet spot: up to -25
Each spam trigger word found: -8 (capped at -30)
Three or more all-caps words, or any word longer than 10 caps: -15
More than one emoji: -10
Excessive punctuation (multiple ! or ?): -10
No personalization signal (name token, "you", "your"): -10
Final open rate grade: 80+ Excellent, 60-79 Good, 40-59 Fair, below 40 Poor
The spam trigger check uses a small built-in list of words that filters and inboxes commonly flag, such as "free", "winner", "guaranteed", "act now", "cash", and similar promotional language. None of these guarantee the spam folder on their own, but stacking several of them raises risk and lowers your subject line score. The personalization check rewards subject lines that speak directly to the reader, since those tend to lift open rates.
A real example
Take the subject line "FREE GIFT!!! Claim your CASH bonus now". It is 39 characters (good length), but it contains three spam triggers ("free", "cash", "now") for -24, it has all-caps words for -15, and excessive punctuation for -10. Starting from 100 that lands around 51, an open rate grade of Fair. Rewriting it as "John, a small thank-you is waiting for you" removes every trigger, keeps a friendly length, and adds personalization, pushing the score into the Excellent range.
Common questions
Is this email subject line tester really free?
Yes. It is completely free with no sign-up, no limits, and no account. Everything runs in your browser and nothing you type is sent to a server.
What is a good subject line length?
Aim for roughly 30 to 50 characters. That range usually displays fully on both desktop and mobile inbox previews, which protects your open rate.
Will a high score guarantee a high open rate?
No. The score is a guideline based on common best practices and a spam trigger check. Your audience, sender reputation, and send time matter too. Treat the result as an estimate, not a promise.
Why are spam trigger words a problem?
Filters weigh many signals, and heavy promotional language is one of them. A single word rarely hurts, but several triggers plus all-caps and lots of punctuation together can push a message toward the spam or promotions folder.
Does adding the reader's name help?
Personalization, like using a name or the words "you" and "your", tends to make subject lines feel relevant, which can improve open rates. The tool gives credit for a personalization signal in its scoring.