How the score works
The score starts at 85 and moves with each check. Length outside 30 to 50 characters, spam-trigger words, ALL CAPS words, repeated exclamation marks, lots of money signs and more than two emoji take points off. A number, a question or a personalization token like {first_name} add a few.
It's a heuristic built on common email marketing advice, not a prediction. Use it to catch mistakes and compare versions, then let your real open rates decide.
How long should a subject line be?
Phones show about 35 to 45 characters of a subject line, depending on the screen and the app. Desktop inboxes show more, often 60 to 70. Since most email is opened on a phone, 30 to 50 characters is a good target, with the important words at the start.
The preview text, the gray line after the subject, is your second headline. If you leave it blank, inboxes show the first words of your email, which is often "View in browser".
Spam-trigger words, caps and punctuation
Modern spam filters care most about your sending reputation and whether people open and engage. Still, words like "free", "act now" and "guaranteed" are a pattern spammers use, and readers skim past them too. Use them sparingly and only when they're true.
- Write in sentence case. ALL CAPS reads as shouting.
- Use one exclamation mark at most.
- One emoji can help you stand out; three looks like spam.
- Never use "RE:" or "FW:" to fake a reply.
What makes people open
Specific beats clever. "3 cozy soups for this week" tells people what they'll get. Curiosity works when it's honest. Personalizing with a first name can help, especially on smaller lists, but always set a fallback so no one gets "Hi ,".
The best test is your own audience. Most email tools can send two subject lines to a small share of your list and send the winner to everyone else.
Subject line formulas worth trying
If you're stuck, start from a proven shape and make it yours. Number plus result: "5 ways to sleep better tonight". Question: "Ready for spring?". News: "New: the autumn menu is here". Deadline: "Last day for free shipping". Personal: "Sam, your order is on its way". Write two, test them, and keep a note of what wins for your list.
Frequently asked questions
What is a good subject line length?
Around 30 to 50 characters, or six to ten words. That shows in full on most phones. Put the key words first in case it gets cut off.
Does the word "free" send emails to spam?
Not on its own. Filters look mostly at your sender reputation and engagement. But a pile of salesy words can hurt, and readers distrust them, so use them only when they're accurate.
Should I use emoji in subject lines?
One emoji can work, especially for casual brands. Test it against a version without. Avoid several in a row, and remember some older inboxes show them as boxes.
Is this score the same as an open rate prediction?
No. It's a checklist of best practices turned into a number. Your list, sender name, timing and past emails affect opens much more.