Intent to Prototype: HTTP/3 protocol upgrade for HTTPS DNS records with h3 alpn parameter

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Tsuyoshi Horo

May 19, 2022, 2:33:08 AMMay 19
to blink-dev,

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HTTPS DNS resource records can provide information about supported protocols such as HTTP/3 with "alpn" parameter. If Chrome receives a HTTPS DNS record indicating HTTP/3 support, Chrome will connect to the server using the HTTP/3 protocol.

Blink component



Currently Chrome can use the HTTP/3 protocol only after receiving an Alt-Svc header from the server using a non-HTTP/3 protocol.  With this new feature, Chrome can connect to the server using HTTP/3 protocol without receiving the Alt-Svc header. This can reduce 1 RTT of handshaking of TCP which is required for non-HTTP/3 protocol while connecting to the server.

Initial public proposal

TAG review

Not applicable. No direct changes to web platform APIs. Change is to the underlying DNS infrastructure.

TAG review status

Not applicable


Interoperability and Compatibility

Gecko: Shipped/Shipping (

WebKit: In development ( Implemented behind "HTTP/3" Experimental Features

Web developers: Strongly positive (

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?



This feature will be debuggable using chrome://net-export/ and

Is this feature fully tested by web-platform-tests?

No. We need an HTTP/3 server and a DNS server to test the feature, and we have neither in WPT.

Flag name


Requires code in //chrome?


Tracking bug

Estimated milestones

No milestones specified

Link to entry on the Chrome Platform Status

This intent message was generated by Chrome Platform Status.

Yoav Weiss

May 19, 2022, 4:06:04 AMMay 19
to Tsuyoshi Horo, blink-dev, Eric Orth
That's great! Thanks for working on this!!

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