Quick answer: The preheader (preview text) is the snippet shown after the subject line in the inbox. This tester previews how your subject and preheader appear on mobile and desktop, counts characters, and flags common mistakes — aim for a 40–100 character preheader that adds to the subject rather than repeating it.
Email preheader & preview text tester
Set preview text on every campaign automatically in Bluey Email — plus subject-line A/B testing on every plan. Test your subject line too.
Why preheader text matters
After the from name and subject, the preheader is the third thing a reader sees — and if you leave it blank, the inbox pulls whatever text is at the top of your email (often “View in browser” or an unsubscribe link). A good preheader extends the subject’s promise, adds urgency or detail, and stays within the ~40–100 characters most clients display. Mobile shows far less, so front-load the important words.
Frequently asked questions
What is a good preheader length?Around 40–100 characters. Desktop clients show more, but mobile often cuts off near 40, so put the key message first.
Should the preheader repeat the subject line?No. Repeating the subject wastes prime inbox space. Use the preheader to add a benefit, detail or call to action the subject does not cover.
What happens if I leave the preheader empty?The email client fills it with the first text in your email — usually something unhelpful like a preheader link or address block. Always set it deliberately.
Is this tool free?Yes — free and private, previewed in your browser.