Email subject line tester
Score your cold email subject line's open-rate potential — the exact length, words and formatting hurting it. Free, private, no signup.
100% client-side — nothing leaves your browser. Best cold subjects are 3–7 words, specific, lowercase, no hype.
Subject line tester FAQ
Is the subject line tester free?+
Yes — free, no signup, 100% client-side (nothing you type leaves your browser).
What makes a good cold email subject line?+
Short (3–7 words / under ~50 characters), specific to the recipient, often lowercase so it reads personal, with no salesy/urgency words, ALL-CAPS or exclamation marks.
Does a high score guarantee opens?+
No — the sender's reputation and inbox placement matter too. A great subject only helps once your mail reaches the inbox, which is what Autocloz's deliverability tooling handles.
Great subject? Now make sure it lands.
Warmup, DMARC/DKIM/SPF and A/B testing built in — so the right people actually see your subject line.