Early-Data Header

Table of Content

The Early-Data header is a feature of HTTP/2 that augments performance boost by allowing the client to send HTTP requests in the first round trip (0-RTT) to the server, before the secure transport (TLS) handshake is complete. This means data can be sent immediately, reducing the time it takes to establish a secure connection and kickstart data exchange.


The syntax for the Early-Data header is quite straightforward:

GET /resource HTTP/1.1
Early-Data: 1


The Early-Data header primarily uses "1" as its directive to indicate that the client intends to send early data.


When a client wants to send early data to a server, it simply includes the Early-Data header with the value set to "1" in its request:

GET /index.html HTTP/1.1
Host: www.example.com
Early-Data: 1

Browser Compatibility

Browser Compatibility
Chrome Not Supported
Firefox Not Supported
Safari Not Supported
Opera Not Supported
Edge Not Supported

As of now, none of the prime web browsers support the Early-Data header.

How to modify Early-Data header

ModHeader is a Google Chrome extension that lets you add or modify HTTP request headers. However, as the Early-Data header is not supported by Google Chrome (and other prime browsers), the extension does not provide the functionality to modify it.