Compression Dictionary Transport
Compression Dictionary Transport is a mechanism for using designated HTTP responses as an external dictionary for future HTTP responses for compression schemes that support using external dictionaries (e.g., Brotli and Zstandard) It is most useful when native HTML semantics or browser capabilities can replace custom implementation work.
Overview
Compression Dictionary Transport is a mechanism for using designated HTTP responses as an external dictionary for future HTTP responses for compression schemes that support using external dictionaries (e.g., Brotli and Zstandard) It is most useful when native HTML semantics or browser capabilities can replace custom implementation work.
Browser support
| Feature | Desktop | Mobile | ||||
|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Safari | Chrome Android | Safari iOS | |
http.headers.Available-Dictionary Experimental | 130 | 130 | | | 130 | |
html.elements.link.rel.compression-dictionary Experimental Valid for link, it defines a Compression dictionary transport that can be used to compress future downloads for resources on this site so the download sizes of those resources are smaller than standard compression. | 130 | 130 | | | 130 | |
http.headers.Accept-Encoding.dcb Experimental A format that uses the Dictionary-Compressed Brotli algorithm. See Compression Dictionary Transport. | 130 | 130 | | | 130 | |
http.headers.Accept-Encoding.dcz Experimental A format that uses the Dictionary-Compressed Zstandard algorithm. See Compression Dictionary Transport. | 130 | 130 | | | 130 | |
http.headers.Content-Encoding.dcb Experimental A format that uses the Dictionary-Compressed Brotli algorithm. See Compression Dictionary Transport. | 130 | 130 | | | 130 | |
http.headers.Content-Encoding.dcz Experimental A format that uses the Dictionary-Compressed Zstandard algorithm. See Compression Dictionary Transport. | 130 | 130 | | | 130 | |
http.headers.Dictionary-ID Experimental The HTTP Dictionary-ID request header references a dictionary that can be used in Compression Dictionary Transport to compress the server's response. | 130 | 130 | | | 130 | |
http.headers.Use-As-Dictionary Experimental The HTTP Use-As-Dictionary response header lists the matching criteria that the Compression Dictionary Transport dictionary can be used for, for future requests. | 130 | 130 | | | 130 | |
Syntax
<!-- Specify dictionary in response header --> <!-- Use-As-Dictionary: match="/js/*" --> <link rel="dictionary" href="/dict/v1.dict"> <script src="/js/app.js"></script>Live demo
Dictionary transport idea
Describe how shared dictionaries can improve compression for repeated payload patterns.
Best-fit scenarios
Compression dictionaries help most when many responses share the same structure or wording.
Operational caution
The feature adds deployment coordination and cache complexity alongside smaller transfers.
Use cases
Control document behavior
Use Compression Dictionary Transport to influence loading, metadata, or script behavior at the document level.
Tune performance strategy
Apply Compression Dictionary Transport when earlier resource hints or document settings improve startup or runtime behavior.
Cautions
- Test Compression Dictionary Transport in your target browsers and input environments before depending on it as a primary behavior.
- Provide a fallback path or acceptable degradation strategy when support is still limited.
Accessibility
- Make sure Compression Dictionary Transport supports the intended task without making the page harder to perceive, understand, or operate.
Related links
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