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Early-Data

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The Early-Data header is set by an intermediate to indicates that the request has been conveyed in TLS early data, and additionally indicates that an intermediary understands the 425 (Too Early) status code. The Early-Data header is not set by the originator of the request (i.e., a browser).

Header type	Request header
Forbidden header name	no

Syntax

Early-Data: 1

Examples

GET /resource HTTP/1.0
Host: example.com
Early-Data: 1

Specifications

Specification	Title
RFC 8470, section 5.1: The Early-Data Header Field	Using Early Data in HTTP

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	?	?	58	No	?	?

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	?	?	?	58	?	?	?

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https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Early-Data