Free Email Subject Line Tester
This free email subject line tester scores your subject from 0 to 100 using eight checks: length, mobile visibility, clarity, specificity, capitalization, punctuation, spam-like phrasing and preview text. Scoring runs in your browser with no signup; only the optional rewrite button sends your line to our AI.
Analyze Your Subject Line
Get an explainable score, detailed checks and three optional AI rewrites.
Subject line score
How to Improve an Email Subject Line
Use the score to find clear mechanical issues, then judge the final line against your audience, offer and brand. A high score cannot guarantee opens.
Pair subject and preview text
The preview should extend the idea instead of repeating it. For fresh campaign angles, use the AI Email Subject Line Generator.
What the Email Subject Line Tester Checks
Every check is a plain rule you can see, so a "Review" result always tells you what to change.
| Check | Passes when |
|---|---|
| Length | 25 to 60 characters |
| Mobile visibility | 45 characters or fewer |
| Clarity | At least three words and a readable message |
| Specificity | A number, percentage or concrete word such as today, guide, report, demo, sale or update |
| Capitalization | Less than half of the letters in capitals |
| Punctuation | No more than one exclamation or question mark |
| Spam-like phrasing | None of: free, guaranteed, act now, buy now, cash, winner, urgent |
| Preview text | If added, it must not repeat the subject line |
A score of 75 or more reads "Strong foundation", 50 to 74 "Needs refinement" and below 50 "Revise before sending".
Using It as an Email Subject Line Spam Tester
The spam-like phrasing check looks for a short list of high-pressure words that often appear in unwanted email. Together with the capitalization and punctuation checks, it catches the subject line habits most likely to look pushy in an inbox.
Inbox placement is decided by more than the subject line. Sender reputation, SPF, DKIM and DMARC authentication, list hygiene and the body of the email all play a part, so treat a clean result here as one step, not a deliverability test.
Getting better versions
After testing, press "Generate 3 improved versions" for AI rewrites that keep your claim, each labelled by what it improves. Test the rewrite you prefer again before sending.
Email Subject Line Tester FAQs
How does the email subject line tester score a subject line?
It runs eight pass or review checks: length, mobile visibility, clarity, specificity, capitalization, punctuation, spam-like phrasing and preview text. The score is the share of checks passed, so each check is worth 12.5 points out of 100.
How long should an email subject line be?
There is no single ideal length. The tester treats 25 to 60 characters as a practical range and flags lines over 45 characters for mobile, because phone inboxes cut long subjects. Put the key words first either way.
Can it test an email subject line for spam?
It flags common high-pressure words such as free, guaranteed, act now, buy now, cash, winner and urgent, plus heavy capitals and stacked exclamation marks. It is not a spam filter: whether an email reaches the inbox also depends on sender reputation, authentication and the email content.
Do you capitalize every word in an email subject line?
Either sentence case or title case is fine, as long as you stay consistent with your brand. The tester only flags a line when more than half of its letters are capitals, because all-caps subjects read as shouting and look spam-like.
What should I put in the subject line of an email?
Put the single most useful thing the email offers, stated specifically: a number, a date, a named guide, report or update. The tester's specificity check looks for concrete details like these.
Is this email subject line tester free?
Yes. The tester is free with no signup and no daily limit on scoring. The score is calculated in your browser, and the three AI rewrites are an optional extra.
Does a high score guarantee more opens?
No. The score catches mechanical problems. Open rates also depend on who the email is from, list quality, timing and how relevant the offer is to the reader.