Email Subject Line Scorer
Score your subject line on length, spam triggers, personalization, specificity, action verbs, and curiosity hooks. Each rule is explained — no black-box magic. Use it before every send.
35 chars (mobile shows ~35)
Clean — no spam triggers
No personalization token detected.
Fix: Add {first_name} or use the recipient's company name — proven to lift open rates 5-15%.
Includes a number.
Passive or noun-led.
Fix: Lead with a verb: 'Ship your', 'Try this', 'Stop doing X'.
No emoji — safe choice.
Question or curiosity hook present.
Frequently asked questions
What's the optimal email subject length?
25–50 characters. Mobile inbox previews truncate at about 30–40 chars (varies by client and screen size). Optimizing for the truncation point — making the first 30 chars carry the value — beats trying to squeeze information into the full 50.
Which words actually trigger spam filters?
Modern Gmail/Outlook spam filters are ML-based, not just keyword matchers — but obvious patterns still raise scores: 'FREE!!!', 'act now', 'click here', '100% guaranteed', dollar signs in clusters ($$$), excessive caps. Our scorer flags the textbook ones; for ML score insight, send through tools like Litmus or Email on Acid.
Does personalization actually lift open rates?
Yes — peer-reviewed studies and platform-level data both show 5–15% lift from using the recipient's first name. The effect is strongest when paired with relevant content; spammy personalization ('JOHN, you won!') hurts more than it helps.
Should I use emoji in subject lines?
Depends on audience. B2C and consumer audiences: one emoji often lifts opens. B2B and professional audiences: emoji can read as promotional and reduce opens. The scorer caps at one — multiple emoji almost always hurts deliverability.