Write a better email subject line before you hit send. Enter your subject line below to get an instant score out of 100, a real-time inbox preview for both mobile and Gmail desktop, and specific feedback on length, spam trigger words, power words, emoji use, and more.
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MiinDigital sets up and runs email marketing for small businesses.
See our email marketing servicesHow to Use the Email Subject Line Tester
- Type your subject line in the input field: the score and feedback update instantly as you write.
- Check the inbox previews: see how your subject line looks when truncated on a mobile device (40 characters) and Gmail desktop (60 characters). Front-load your key message.
- Read the feedback: each check flags specific issues or strengths: spam trigger words, length, power words, emoji usage, numbers, and personalisation tokens.
- Refine your subject line until you reach a score of 65 or higher. Test multiple variations and pick the strongest one.
What Makes a Strong Email Subject Line?
- Length: 40–60 characters: long enough to be descriptive, short enough to display fully on most email clients. Mobile typically cuts off after 40 characters, so put your hook first.
- Go easy on spammy phrasing: modern filters care more about your sender reputation and engagement than single words, but a subject like “FREE!!! Act now” still looks like spam to readers and filters alike.
- Use active words: words like “discover”, “save”, “new” and “you” make the benefit clear.
- Include a number: “5 tips” or “save 30%” is more specific and credible than a vague promise.
- Ask a question: questions create curiosity and a natural pull to open the email for the answer.
- Use personalisation carefully: a first name or city can help, but only when your data is clean.
- Use emoji sparingly: one relevant emoji can stand out in a busy inbox. More than two starts to look spammy.
- Avoid excessive punctuation: multiple exclamation marks (“!!!”) are a strong spam signal and reduce credibility.
Email Subject Line Length by Email Client
- iPhone (iOS Mail): ~35–40 characters before truncation in the inbox list view.
- Android Gmail app: ~40 characters visible in list view.
- Gmail desktop: ~60 characters before the subject line is cut off in the inbox.
- Outlook desktop: ~60–70 characters depending on screen width.
- Apple Mail (macOS): ~60–80 characters depending on window width.
The safest strategy is to keep your subject line under 50 characters and place your most important words in the first 35–40 characters. This ensures the key message is visible regardless of the device.
Frequently asked questions
What is a good email subject line score?
A score of 65 or above is good. 80 or above is excellent. Scores below 45 indicate significant issues, usually too many spam words, poor length, or missing engagement signals like power words or numbers.
Does a high score guarantee better open rates?
Not guaranteed, open rates also depend on your sender reputation, list quality, send time, and audience segment. A high score means your subject line follows best practices that are statistically correlated with better performance. Always A/B test your subject lines when possible.
What are spam trigger words?
Words and phrases that are common in spam, like “winner”, “guaranteed” or “act now”. A single word rarely gets an email filtered on its own; filters weigh your sender reputation, authentication and engagement far more. But spammy wording on top of other warning signs does add up, and it puts readers off.
Should I always use personalisation?
Personalisation is highly effective when your list data is accurate and up to date. Incorrect personalisation (“Hi {first_name}”) is worse than no personalisation at all. Use it when you’re confident in your data quality.
Is this tool free?
Yes, completely free with no account required. All analysis happens in your browser, no email data is sent to any server.
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