Your subscribers decide in 2 seconds whether to open your email. Our AI scores your subject line, tells you exactly what's wrong, and generates better alternatives — all free.
Test Your Subject Line Free 5 free tests per month. No signup required.That number comes from research by Convince & Convert, and it's been replicated across multiple email marketing studies. Nearly half your recipients never look at the sender name, the preview text, or anything else. They see the subject line, and they decide: open or ignore.
The flip side is even scarier: 69% of recipients report email as spam based solely on the subject line (Invesp). One bad subject line doesn't just lose an open — it can get you flagged, tanking your sender reputation and deliverability for future campaigns.
Yet most businesses write subject lines as an afterthought. They spend hours on email copy, design, and segmentation, then dash off a subject line in 10 seconds. That's like building a beautiful storefront and forgetting to put up a sign.
The data is clear on what works: subject lines between 6-10 words get the highest open rates. Personalized subject lines are 26% more likely to be opened (Campaign Monitor). And subject lines that create curiosity or urgency consistently outperform generic announcements.
Our subject line tester analyzes all of these factors — word count, emotional triggers, spam words, personalization, mobile readability — and gives you a score plus specific improvements.
These are real examples showing how small changes to a subject line can dramatically improve predicted open rates.
These aren't opinions — they're patterns backed by data from billions of emails analyzed across major email marketing platforms.
Subject lines in this range have the highest open rates according to data from Mailchimp and HubSpot. Shorter than 6 words feels incomplete. Longer than 10 gets cut off on mobile, where 46% of emails are opened.
Mobile screens show roughly 30-35 characters. If your key message is at the end of a 60-character subject line, most people will never see it. Put the hook first.
"5 ways to reduce your tax bill" outperforms "Ways to reduce your tax bill" every time. Numbers are specific, scannable, and set clear expectations.
"What we found when we analyzed 10,000 cold emails" makes you want to know the answer. "You won't BELIEVE what happened next!!!" makes you want to unsubscribe. There's a line.
All caps triggers spam filters and feels like shouting. Multiple exclamation marks signal desperation. Use sentence case and one punctuation mark maximum.
Using a subscriber's name increases open rates by 26%. But the real power is in relevant personalization: their city, their purchase history, their industry. "Your Austin store has new inventory" beats "Hi John, check out our sale."
Even experts guess wrong. Send version A to 15% of your list, version B to another 15%, then send the winner to the remaining 70%. Most email platforms support this natively.
Clickbait subject lines might boost one open rate, but they destroy trust and increase unsubscribes. If you promise "3 tips," deliver exactly 3 tips. Consistency builds a readership that opens every email you send.
Every email you send without testing the subject line is leaving opens on the table. Score yours in 5 seconds.
Test Your Subject Line Free