Early dataLimited availability
TLS 1.3 sessions may be resumed more quickly by sending so-called early data to servers before the TLS handshake has finished. Also known as zero round-trip time resumption or 0-RTT.
Not yet supported in all major browsers — check the table and provide a fallback.
Browser support
DesktopChrome
✕Not supportedup to 155
Current: 155Edge
✕Not supportedup to 154
Current: 154Firefox
1–57Not supported
58+Supportedsince Jan 23, 2018
Current: 157Safari
✕Not supportedup to 27
Current: 27MobileChrome Android
✕Not supportedup to 155
Current: 155Firefox Android
4–57Not supported
58+Supportedsince Jan 22, 2018
Current: 157Safari iOS
✕Not supportedup to 27
Current: 27How to use
Not supported in Chrome, Edge, Safari, Chrome Android, Safari iOS. Use feature detection below and provide a fallback (or a polyfill) for those browsers.
Example
Full syntax and examples are on MDN: Early-Data.
Feature detection
There’s no simple runtime check for this feature; rely on the support table and test in your target browsers.
Documentation (MDN)
Specification
Sub-features
Support for each part of the feature (2). The overall table above shows when the whole feature works.
| Sub-feature | Chrome | Edge | Firefox | Safari | Chrome Android | Firefox Android | Safari iOS |
|---|---|---|---|---|---|---|---|
| http.headers.Early-Data | ✕ | ✕ | 58 | ✕ | ✕ | 58 | ✕ |
| http.status.425 | ✕ | ✕ | 58 | ✕ | ✕ | 58 | ✕ |