Use-As-Dictionary header

Limited availability

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

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

The HTTP Use-As-Dictionary response header lists the matching criteria that the Compression Dictionary Transport dictionary can be used for, for future requests.

See the Compression Dictionary Transport guide for more information.

Syntax

http

Use-As-Dictionary: match=""
Use-As-Dictionary: match-dest=("" "", …)
Use-As-Dictionary: id=""
Use-As-Dictionary: type="raw"

// Multiple, in any order
Content-Encoding: match="", match-dest=("")

Directives

match: A string value containing a URL Pattern: only resources whose URLs match this pattern may use this resource as a dictionary.
match-dest: A space-separated list of strings, with each string in quotes and the whole value enclosed in parentheses, that provides a list of Fetch request destinations that requests must match if they are to use this dictionary.
id: A string value that specifies a server identifier for the dictionary. This ID value will then be added in the Dictionary-ID request header when the browser requests a resource which can use this dictionary.
type: A string value that describes the file format of the supplied dictionary. Currently only raw is supported (which is the default) so this is more for future compatibility.

Examples

Path prefix

http

Use-As-Dictionary: match="/product/*"

This says the dictionary is only to be used for URLs starting with /product/.

Versioned directories

http

Use-As-Dictionary: match="/app/*/main.js"

This uses a wildcard to match multiple versions of a file.

Destinations

http

Use-As-Dictionary: match="/product/*", match-dest=("document")

This uses match-dest to ensure the dictionary is only used for document requests so