OpenAPI Extensions
The x- namespace is where API providers put everything OpenAPI would not
hold — documentation, lifecycle, policy, provenance, pricing, and lately agents. It is
the largest undocumented vocabulary in the API space, and almost none of it is written
down anywhere a person or an agent can look it up. This is that reference, built by
reading every as-published OpenAPI in the catalog.
Descriptions are derived from evidence, not from published definitions —
where a key appears, what its value looks like, and who uses it. Most extensions have no
published definition to quote. Read them as observation.
326 entries are HTTP header names rather
than true extensions; they are kept and flagged, because dropping them would hide why the
namespace looks larger than it is.
| Extension | Purpose | What it appears to do | Uses | Providers |
|---|