Data & schema semantics

x-api-version

`x-api-version` appears on operations and at the root of the document. Its value is a string. Used by 7 providers across 23 OpenAPI documents. Observed values include `1`, `4.4.0`, `4.0.2`, `2025-01-01`. Consistent with data & schema semantics — this is inferred from where the key appears and what it carries, not from any published definition.

Data & schema semantics derived description
How this description was produced. It is assembled from what was measured in the corpus — where this key appears in a document, what shape its value takes, the values observed, and how many providers use it. It is not taken from a published definition, because for most extensions none exists. Read it as evidence, not as a specification. If you own this extension and want it described properly, tell us.
58 occurrences
23 documents
7 providers
purpose-named

Where it appears

Location in the documentOccurrences
root 17
operation 26
schema 1
info 2
header 12

What its value looks like

Value shapeOccurrences
string46
object12

Observed values

Sampled from the specifications, most frequent first.

14.4.04.0.22025-01-013.1.02.9.13.3.0v1

Providers publishing it

All 7.

factsetgo1relativityrocksolidspaceflight-newsvisawiden

Why this is not in OpenAPI

Extensions exist because a provider needed something the specification would not carry. Most of what they hold is not the API contract at all — it is operational metadata about the contract: documentation, lifecycle, policy, provenance, and now agents. That metadata is usually better placed alongside the contract, in an Overlay or an APIs.json index, than crammed inside it. See everything else doing the data & schema semantics job.