Is the Subject Line Tester free to use?

Yes, the Subject Line Tester is completely free. There is no sign-up, no account required, and no limit on how often you can use it.

Does the Subject Line Tester use AI?

The Subject Line Tester uses standard algorithms and rule-based logic, not AI or machine learning. Your text is processed in your browser only and is not sent to any external service.

What devices does the Subject Line Tester work on?

The Subject Line Tester works on any device with a modern web browser — desktop, laptop, tablet, or phone. It is mobile-friendly and works offline once the page has loaded.

✍️ Writing & SEO

Email Subject Line Tester

Score any email subject line for open rates. Checks length, power words, numbers, emojis and spam trigger words. Free.

The Subject Line Tester is a free online tool that helps you score any email subject line for open rates. checks length, power words, numbers, emojis and spam trigger words. free It runs in your browser with no sign-up, downloads, or installation needed. All processing happens locally — your data stays on your device.

Enter your email subject line

How to use

What makes a great subject line?

The ideal email subject line is 30–50 characters long, creates curiosity or urgency, includes the recipient's benefit, and avoids spam trigger words. Personalisation tokens like first names improve open rates significantly. Numbers and emojis can boost open rates when used sparingly and appropriately.

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