Free Tool

Subject Line Tester

Analyze your email subject line for spam triggers, length, readability, and engagement signals. Get an instant score with actionable tips.

10-point analysis
50+ spam triggers checked
Real-time scoring

0 characters · 0 words

Why subject lines matter

First impression

Your subject line is the first thing recipients see. 47% of email recipients open emails based on the subject line alone.

Spam filters

Certain words and patterns trigger spam filters. Avoid ALL CAPS, excessive punctuation, and known spam trigger words.

Optimal length

Subject lines between 30-60 characters perform best. Longer lines get truncated on mobile devices, hiding your message.

Personalization works

Personalized subject lines are 26% more likely to be opened. Use merge tags like {{first_name}} to increase engagement.