Performance & quality

x-400

`x-400` appears on response objects. Its value is a string. Used by 4 providers across 4 OpenAPI documents. Observed values include `User not opt-in:`, `Invalid configuration:`, `Reference No Not found:`, `Transaction already canceled:`. Consistent with performance & quality — this is inferred from where the key appears and what it carries, not from any published definition.

Performance & quality 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.
11 occurrences
4 documents
4 providers
purpose-named

Where it appears

Location in the documentOccurrences
response 9
operation 2

What its value looks like

Value shapeOccurrences
string9
object2

Observed values

Sampled from the specifications, most frequent first.

User not opt-in:Invalid configuration:Reference No Not found:Transaction already canceled:From Date is greater than To Date Copy:No Record Found:Date difference cannot be more than 15 days:Invalid Transaction Type Update:

Providers publishing it

All 4.

airalobalad-corpklarnaxiaoman

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 performance & quality job.