Free Tool
Email Subject Tester
Test any subject line for open-rate strength, spam risk, and rewrite angles you can use immediately.
0 words0 characters
Enter a subject line to see score and rewrite ideas.
How to write high-open-rate subject lines
Use this free email subject line analyzer to test one variable at a time. Start with a direct benefit, add one concrete detail, then test curiosity vs direct-response framing.
- Aim for 4-9 words and roughly 28-52 characters for mobile readability.
- Include one measurable promise like a number, time window, or specific outcome.
- Avoid spam triggers and over-punctuation to protect inbox placement.
Related tools: Headline Scorecard ยท Reel Analyzer
Email Subject Tester FAQ
What is a good email subject line length?
For most audiences, 4-9 words and under ~52 characters performs well because mobile inboxes truncate long subject lines.
Does this tool improve deliverability?
It helps reduce obvious spam signals and weak phrasing. Deliverability also depends on sender reputation, domain setup, and list quality.
Should I use curiosity or direct benefit?
Test both. A practical baseline is one direct-benefit version, one curiosity version, and one urgency version in every campaign split test.