Email Subject Line Tester
Type a subject line and, if you have it, the preview text. You get a score out of 100 and, more usefully, the reason for every point it gained or lost.
37 characters
0 characters. The line shown after the subject in most inboxes.
90/100
Strong
Length (Good)
37 characters. Short enough that the whole line is likely to show on a phone.
25/25
Word count (Good)
7 words. Easy to take in at a glance.
10/10
Spam and pressure words (Good)
None of the words on the caution list.
20/20
Capital letters (Good)
No shouting.
15/15
Punctuation (Good)
Calm punctuation.
15/15
Emoji (Good)
No emoji. Nothing to go wrong.
5/5
Personalization (Note)
No merge tag. Not required: an email about something the reader wants beats one that only knows their name.
3/5
Preview text (Could be better)
No preview text. The inbox will show the first words of the email instead, often "View in browser" or an image description.
5/15
Honest framing (Good)
Does not pretend to be a reply or a forward.
10/10
Specifics (Good)
Has a number: a price, a date, a count. Specifics tell the reader what they get.
5/5
How the score works
The tester runs ten checks. Each one has a fixed number of points, and the score is the points earned divided by the points available. There is no model and no hidden weighting: the same line always gets the same score, and every check tells you what it saw.
The score is not a prediction of your open rate. Opens depend far more on who you send to, how often, and whether they trust your name in the From line. What the checks catch are the things that reliably make a line harder to read or easier to ignore.
The ten checks, and their points
- Length, 25 points. Full marks from 20 to 45 characters. Phones cut long lines off and where depends on the app and screen, so the important words belong first.
- Word count, 10 points. Three to nine words is easy to take in at a glance.
- Spam and pressure words, 20 points. Seven points off for each phrase from a caution list ("act now", "risk free", "winner"...).
- Capital letters, 15 points. Whole words in capitals read as shouting. Common acronyms like BFCM or SPF are allowed.
- Punctuation, 15 points. "!!!" or "?!" score nothing; one exclamation mark loses a little.
- Emoji, 5 points. One is fine; three or more read as decoration.
- Personalization, 5 points. A merge tag earns full marks, with a reminder to set a fallback. Without one you still get 3: it is optional.
- Preview text, 15 points. Full marks for 35 to 100 characters that add something the subject does not.
- Honest framing, 10 points. A fake "RE:" or "FW:" scores zero.
- Specifics, 5 points. A number (a date, a size, a price) earns full marks.
A worked example
"LAST CHANCE!!! 50% OFF EVERYTHING 🔥🔥" with no preview text scores 65 (Needs work). It keeps full marks for length, word count, specifics and spam words, but loses all 15 for capitals, all 15 for punctuation, 2 for the second emoji, 10 for the missing preview text and 2 for having no merge tag.
Rewritten as "Last chance: 50% off ends at midnight", with the preview "Everything in the autumn range, including the linen throws. Ends 11:59pm.", it scores 98 (Strong). Same offer, same urgency; the only point it misses is the optional merge tag.
Common subject line mistakes
- Leaving preview text empty. The inbox then shows the first text in your email, which is often "View in browser" or an image description.
- Repeating the subject in the preview. It is a second line of copy: use it for the detail, the deadline or the reason to open.
- Pretending to be a reply. Beyond the trust it costs, the US CAN-SPAM Act says a subject line must accurately reflect the content of the message.
- Writing for the desktop. Test on a phone, where most of the line may be cut.
- Judging a line by one send. To know if a line works better, test it against another on the same audience at the same time.
Rules worth knowing
Under CAN-SPAM, deceptive subject lines are not allowed: the subject has to reflect what is in the email. source, checked 25 September 2026
Gmail’s sender guidelines ask all senders to keep the spam rate reported in Postmaster Tools below 0.3%, and bulk senders to support one-click unsubscribe. A subject line that makes people hit "Report spam" costs you more than one campaign. source, checked 25 September 2026
What the tester does not know
It cannot see your list, your sending history or your brand, so it cannot tell whether a line fits your voice or will land with your customers. The spam words are a caution list, not a blocklist: filters weigh your reputation more than any word. To find out which of two good lines actually wins, send both to a split of your list and check the result with the A/B test significance calculator.
Questions people ask
What is a good length for an email subject line?
There is no single number, because inboxes cut lines by width, not by characters. The tester gives full marks from 20 to 45 characters, where the whole line is likely to show on a phone, and asks you to put the important words in the first 30 or so.
Do spam trigger words still matter?
Less than they used to. Mailbox providers judge mostly on sender reputation and how people react to your mail. The words still make an email look like the kind people learned to ignore, and they add up with other signals.
Should I use emoji in subject lines?
One can work if it suits your brand. Check it on a phone and in an older mail app, where some emoji display differently. Several in one line crowd out the words.
What is preview text?
The line that shows after or under the subject in most inboxes. You set it in your email platform. If you do not, the inbox shows the first text it finds in the email.
Is the score a prediction of my open rate?
No. It checks things that make a line harder to read or easier to ignore. Your open rate depends mostly on your list, your timing and whether people know and trust the sender.
Written by Tilly. Free to use with no sign-up. The tool runs in your browser, and nothing you type into it is sent or stored.
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