Available-Dictionary header

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

See full compatibility

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

The HTTP Available-Dictionary request header allows the browser to specify the best matching dictionary it has to allow the server to use Compression Dictionary Transport for a resource request.

Clients can send an Available-Dictionary header when they support dcb or dcz encodings. The header is a colon-surrounded base-64 encoded SHA-256 hash of the dictionary contents.

See the Compression Dictionary Transport guide for more information.

Syntax

http

Available-Dictionary: :<base64-hash>:

Directives

<base64-hash>: A base-64 encoded SHA-256 hash of the dictionary contents.

Examples

http

Accept-Encoding: gzip, br, zstd, dcb, dcz
Available-Dictionary: :pZGm1Av0IEBKARczz7exkNYsZb8LzaMrV7J32a2fFG4=:

Specifications

Specification
Compression Dictionary Transport # name-available-dictionary

Browser compatibility

	desktop					mobile
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on iOS	Samsung Internet	WebView Android	WebView on iOS
`Available-Dictionary` Experimental	Chrome – Full support Chrome 130 (Release date: 2024-10-15) footnote Full support	Edge – Full support Edge 130 (Release date: 2024-10-17) footnote Full support	Firefox – No support Firefox footnote footnote See bug 1917974	Opera – Full support Opera 115 (Release date: 2024-11-27) footnote Full support	Safari – No support Safari footnote No support	Chrome Android – Full support Chrome Android 130 (Release date: 2024-10-15) footnote Full support	Firefox for Android – No support Firefox for Android footnote footnote See bug 1917974	Opera Android – Full support Opera Android 86 (Release date: 2024-12-02) footnote Full support	Safari on iOS – No support Safari on iOS footnote No support	Samsung Internet – Full support Samsung Internet 28 (Release date: 2025-04-02) footnote Full support	WebView Android – Full support WebView Android 130 (Release date: 2024-10-15) footnote Full support	WebView on iOS – No support WebView on iOS footnote No support

Tip: you can click/tap on a cell for more information.

Full support: Full support
No support: No support
: Experimental. Expect behavior to change in the future.
: See implementation notes.