Data & schema semantics

x-Error

`x-Error` appears on schema objects and properties. 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

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.

Also published under another name. This key exists in the wild spelled more than one way — differing only by case or a hyphen, which means no tool can treat them as the same thing: x-error. Each is catalogued separately here because that is how they exist.

9 occurrences

1 documents

1 providers

purpose-named

Where it appears

Location in the document	Occurrences
schema	9

What its value looks like

Value shape	Occurrences
object	8
string	1

Observed values

Sampled from the specifications, most frequent first.

ErrorCode:Sw.Stds.D00008, ErrorText:Invalid BIC., Severity:Fatal

Providers publishing it

All 1.

citi

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.