Free tool · Scored as you type
Would you open
this subject line?
Eight checks tuned for cold email — not newsletters. See your subject the way Gmail shows it, on desktop and on a phone, before a single prospect does.
Scored as you type, entirely in your browser. The link in your address bar reproduces this exact test.
What 100,000+ cold emails teach about subjects
Short wins because mobile decides
More than half of B2B email gets triaged on a phone, where ~38 characters survive. If your point lives in character 50, it doesn't exist.
Curiosity beats clarity — barely
'quick question' style subjects open well precisely because they withhold. But the email body must pay that curiosity off fast, or the reply rate dies where the open rate thrived.
Lowercase is a feature
An all-lowercase subject reads as dashed-off and personal. It's a small dishonesty with a big effect — use it only if your email genuinely is personal.
The subject's real job is the second email
A great subject that doesn't match the body earns an open today and a spam report tomorrow. Filters track that. Write the subject the body deserves.
Questions, answered honestly
What makes a good cold email subject line?
It looks like an email from a colleague: 2–8 words, sentence case, specific, zero hype. 'quick question about the Q3 rollout' beats 'Unlock Explosive Growth Today!' every single time, because the first one gets opened out of curiosity and the second gets reported out of reflex.
How is the score calculated?
Eight checks, each tuned for cold outreach rather than newsletters: length, word count, spam-trigger phrases, ALL CAPS, exclamation marks, emoji, Title Case and personalization tokens. Warnings cost a few points, hard failures cost more. The score is a writing aid, not a deliverability guarantee.
Do spam words in the subject really send email to spam?
Not by themselves — modern filters weigh sender reputation and engagement far more than word lists. But trigger phrases correlate with low engagement and high report rates, and those do sink you. Think of the word check as a 'does this smell like marketing?' test.
Should subject lines be personalized?
Yes, when the personalization is real. {{company}} or a detail only that prospect recognizes lifts opens meaningfully. Fake personalization ('John, a gift for John!') does the opposite. The tester detects merge tags and reminds you to check the fallback.
Why does the tool penalize Title Case?
Because Capitalizing Every Word is how headlines and ads are written, not how humans write emails to each other. Cold email works when it's indistinguishable from a real one-to-one message — sentence case is part of that disguise.
Keep going
More free tools
Spam Word Checker
Same trigger-phrase scan, applied to your whole email body with in-place highlights.
Cold Email Prompt Library
AI prompts for subject lines, first lines and follow-ups that don't sound like AI.
Cold Email ROI Calculator
See what a better open rate is worth in actual meetings and revenue.
Stop guessing. Test subjects on real sends.
Norbelys A/B tests subject lines on live sends and picks winners from replies by real humans — not bot opens. The testing you'd do by hand, running on every campaign.
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