Email Subject Line Optimizer
Score email subject lines 0-100 with heuristics for length, spam triggers, emoji and personalization.
About this tool
Scores each email subject line from 0-100 using transparent heuristics and lists the factors that helped or hurt plus concrete suggestions. It checks ideal length and word count, emoji use, ALL-CAPS, spam-trigger words, personalization tokens, numbers, questions and excessive punctuation. Built for email marketers refining open rates; it is heuristic, not AI.
Frequently asked questions
What makes a good email subject line length?
Roughly 30-50 characters and 4-9 words tends to display fully and read well, especially on mobile. The tool penalizes lines outside that range.
Why does my subject line score low?
Common culprits are spam-trigger words (free, guarantee, act now, $$$), ALL-CAPS words, more than two emoji, and excessive punctuation like !!! - the breakdown lists exactly what hurt.
Is this scoring AI-based?
No, it uses transparent heuristics for length, word count, emoji, caps, spam words, personalization tokens, numbers and questions. Always A/B test with your real audience.