Email Subject Line Tester & Previewer
Optimize your email subject line and preheader text. See live rendering across mobile and desktop devices, prevent truncated headlines, and boost email open rates.
Mobile inboxes truncate subject lines around 35-42 characters. Place your core value proposition first!
Desktop clients show the subject line and preheader sequentially separated by a hyphen.
What is the Ideal Subject Line Length?
Over 60% of emails are opened on mobile devices where screens cut off subject lines after roughly 35 to 45 characters. To ensure your message is communicated completely, place your strongest hook in the first 35 characters, and use the preheader text for secondary context.
Why Does Preheader Text Matter?
If you leave the preheader empty, email clients will grab random text from your email HTML (often "View in browser" or "Unsubscribe"). A deliberate preheader acts as a one-two punch with your subject line to double open rates.
Automate high-deliverability email marketing
CentricSell Mail provides automated IP warmup, multi-ESP failover, and comprehensive open/click analytics.