Data & schema semantics

x-ratelimit-first-call

`x-ratelimit-first-call` appears on header objects. Its value is a structured object. Used by a single provider across 1 OpenAPI document. 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 HTTP header, not an extension

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.

This is an HTTP header name, not a vendor extension. It appears under a headers: map, which is the same syntactic position an extension key occupies — but OpenAPI models headers natively and this is not extending anything. It is listed here because it turns up when you inventory the x- namespace, and leaving it out would hide why the namespace looks bigger than it is.

5 occurrences

1 documents

1 providers

purpose-named

Where it appears

Location in the document	Occurrences
header	5

What its value looks like

Value shape	Occurrences
object	5

Providers publishing it

All 1.

limble-cmms

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.