Paste your subject line and get an instant score out of 100, plus the exact things that could hurt your open rate or send you to the Promotions tab, with how to fix each one. Nothing you type leaves your browser.
100% private. This runs entirely in your browser, nothing is uploaded or stored.
A good subject line only matters if the email lands in the inbox in the first place. Writing the emails and making sure they get read is exactly what we do for clients. Send us your last campaign and we will tell you what is really holding your opens back.
A good email subject line is short, specific and written the way you would message one person: about 20 to 50 characters, no spam-trigger words, no shouting in capitals and no fake urgency. A subject line tester catches those mistakes before you send. It cannot predict your open rate, which also depends on your list, your sender name and whether the email reaches the inbox.
Who this is for: Coaches, creators and founders writing newsletters, launch emails and sequences.
| What it does | Scores an email subject line out of 100 and lists each problem with a fix. |
| Who it is for | Anyone about to send a newsletter, launch email or campaign. |
| You put in | One subject line. Merge tags like {{first_name}} are fine. |
| You get | A score, a verdict, a checklist worst first, and a shareable score card. |
| What it checks | Spam-trigger words, length in characters and words, capitals, punctuation, prices and percentages, emoji, fake Re: or Fwd: prefixes, and personalisation. |
| Runs | In your browser. Nothing you type is uploaded or stored. |
| Price | Free. No sign-up. |
Last reviewed 29 October 2026 by Mohamed Bashir.
The subject line has two jobs. It has to get past the filters, and then it has to make one busy person want to open. Both reward the same thing: a line that reads like a person wrote it to them, about something they care about.
In practice that means short and specific. "Your welcome email is losing half your sign-ups" beats "Big news inside!!" every time, because it names a problem the reader has. For more examples and patterns, read how to write catchy email subject lines.
Every subject line starts at 100. Each problem takes points off, and the score cannot go below 0.
| Check | Points off | When |
|---|---|---|
| Spam-trigger words | 7 per word, up to 24 | A phrase from a list of about 60 money, urgency and spam phrases appears |
| Fake Re: or Fwd: | 12 | The line starts with Re:, Fwd: or Fw: |
| Too long | 10, or 5 | More than 62 characters, or 51 to 62 |
| Capitals | 9 | A word of three or more capital letters (FYI, ASAP, PDF and FAQ are allowed) |
| Stacked punctuation | 9 | !!, ??, ?! or !?. A single exclamation mark costs 3 |
| Emoji | 8, or 4 | Three or more emoji, or two |
| Prices or percentages | 6 | A £, $ or € sign, or a number with % |
| "FREE" in capitals | 6 | The word FREE written in capitals |
| Too many words | 5 | More than 12 words |
| Very short | 3 | Fewer than 15 characters |
80 or more is a strong subject line, 60 to 79 is okay but could be tighter, and under 60 is likely to hurt opens. The word list, the points and the bands are our own judgement from writing and testing emails, not rules published by Gmail or Outlook.
If your opens are low no matter how good the subject lines are, the emails may not be reaching the inbox at all. That is the work our email deliverability service does.
Words that promise money or urgency are the worst: free, cash, guarantee, act now, limited time, winner, risk-free, and anything with prices or percentages. One is usually survivable. Two or three together, especially with an exclamation mark, is what tips a subject line into the Promotions tab or spam.
Aim for roughly 20 to 50 characters, or about four to nine words. Most phones show only the first 40 or so characters, so front-load the point. Very short subject lines can work well when they read like a real person wrote them.
One emoji is fine and can lift opens if it fits your voice. Two or more start to read as marketing and can nudge you toward Promotions. If you sell to businesses, plain text usually beats emoji.
No. Open rates depend on who is on your list, whether the email reaches the inbox, your sender name and timing, and Apple Mail inflates opens for many lists. A tester catches avoidable mistakes. Only a real send, or an A/B test, tells you which line wins.
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