Preview how your subject line and preheader appear in Gmail, iPhone Mail, and Android before you hit send.
| Platform | Subject limit | Your length | Status |
|---|---|---|---|
| Gmail Desktop | 77 chars | 0 | ✓ |
| iPhone Mail | 35 chars | 0 | ✓ |
| Android Gmail | 40 chars | 0 | ✓ |
A preheader (also called preview text) is the short snippet of text that appears after the subject line in most email inboxes. It is pulled from the first visible text in the email body — or you can set a dedicated hidden preheader element in your HTML. A compelling preheader extends your subject line's message and can significantly improve open rates.
Most email marketers recommend keeping subject lines under 40–50 characters for best mobile compatibility. Gmail desktop shows roughly 77 characters of combined subject and preheader. iPhone Mail truncates the subject at around 35 characters, and Android Gmail at around 40 characters. Front-load your key message so it is visible on all devices.
Desktop email clients display wider inbox rows, so they can show more subject and preheader text. Mobile inboxes have narrower screens and larger fonts, which means fewer characters fit before the text is truncated. The exact cutoff also varies by device screen width, font size setting, and the mail app in use.
Research consistently shows that shorter subject lines (under 40 characters) perform well on mobile. However, the best subject line is one that is specific, creates curiosity or urgency, and is relevant to the recipient — length alone does not determine open rates. Run A/B tests to find what resonates with your audience.
Use this free previewer to see how your subject and preheader appear across Gmail desktop, iPhone Mail, and Android Gmail. For deeper testing, most email platforms (Mailchimp, Klaviyo, Campaign Monitor) have built-in inbox preview tools. You can also send test emails to accounts on different devices and email clients before launching a campaign.