v156 · capability detection

Client-observable probe

Not every part of this feature needs a cooperating server. These checks read what the browser exposes directly — the recognised link relation keyword, the resource-timing surface that can reveal dcb/dcz after the fact, and the secure-context prerequisite — each a real read, run live below.

Run the client-side checks

These probe exactly the surfaces the platform exposes to a page, with no server round trip. A pass proves only that specific client-observable contract.

  1. link.relList.supports("compression-dictionary")

    not run

  2. A <link> accepts rel="compression-dictionary"

    not run

  3. PerformanceResourceTiming.contentEncoding

    not run

  4. Secure context (required for the feature)

    not run

What each check does and does not prove

relList.supports("compression-dictionary") confirms the browser recognises the link relation keyword — it has since Chrome 130, so a pass here does not imply the v156 request-semantics update; that is only visible on the server (see the link-request-semantics concept). PerformanceResourceTiming.contentEncoding is the one client-side way to confirm a response actually arrived as dcb/dcz; where it is absent, you cannot verify the encoding from the page at all. The secure-context check reflects a hard prerequisite: the feature does nothing on plain HTTP.

see also