demo · v130

Shared CDT simulator

Edit a dictionary (the previous version) and the new resource. The page posts both to a local server route, measures real regular Brotli bytes plus a real dictionary-compressed payload, then shows the request/response headers Chrome and a server would negotiate for dcb/dcz.

Measured, with one honest caveat: the baseline Brotli and dictionary-compressed payload are produced by the server. Native JavaScript does not expose a Shared Brotli or Zstandard dictionary encoder, so the dcb result uses RFC 9842's 36-byte dcb header plus a real zlib dictionary-compressed payload as the local stand-in.

Dictionary (previous response, served once and cached)

New response (this fetch)

Waiting for measurement...

raw

0
bytes

regular Brotli

0
bytes

dictionary result

0
bytes (saving 0% vs Brotli)

request & response headers


    

  


  

    
the wire format


# 1. Server advertises that future responses can be encoded
#    against a dictionary, by serving the dictionary once with:
Use-As-Dictionary: match="/app.*.js", id="v42"

# 2. On the next fetch, Chrome sends:
Available-Dictionary: :<sha-256 of dictionary>:
Accept-Encoding: gzip, deflate, br, zstd, dcb, dcz

# 3. Server responds with the diff:
Content-Encoding: dcb
Vary: accept-encoding, available-dictionary

  


  

    
see also