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Email Subject Tester
Check an email subject line’s length, spam-trigger words and punctuation, and preview it in a desktop and mobile inbox.
Inbox preview
What works: 30–50 characters (about 4–9 words) fits every inbox, mobile included. Lead with the benefit, be specific, and use the preheader to add a second reason to open. The score is a guide based on common deliverability and open-rate advice — always A/B test on your own list.
About the Email Subject Tester
The Email Subject Line Tester checks your subject for length, spam-trigger words, excessive capitals and punctuation, and emoji, and previews how the sender name, subject and preheader look in desktop and mobile inboxes. Better subject lines lift open rates and help your emails avoid the spam folder.
How to use the Email Subject Tester
- Enter your subject line.
- Add the sender name and preheader text.
- Read the score and the warnings about length, spam words, caps and emoji.
- Check the desktop and mobile inbox previews and refine your wording.
Frequently asked questions
How long should an email subject line be?
Around 30–50 characters works well. Mobile inboxes usually show only the first 30–40 characters.
What is a preheader?
The preheader is the short preview text shown after the subject in most inboxes. Using it well adds context and can raise opens.
What are spam trigger words?
Phrases such as “free money”, “act now” or “100% guaranteed” are often linked with spam. Using them, especially with capitals and exclamation marks, can hurt deliverability.