x-filename-id
`x-filename-id` appears on operations. Its value is a string. Used by a single provider across 1 OpenAPI document. Observed values include `rest-api-v1.3-campaigns-campaignname-sms-trigger-post`, `rest-api-v1.3-user-info-get`, `rest-api-v1.3-settings-account-get`, `rest-api-v1.3-settings-account-endpoint-get`. Consistent with identity & relationships — this is inferred from where the key appears and what it carries, not from any published definition.
Where it appears
| Location in the document | Occurrences | |
|---|---|---|
| operation | 88 |
What its value looks like
| Value shape | Occurrences |
|---|---|
| string | 88 |
Observed values
Sampled from the specifications, most frequent first.
Providers publishing it
All 1.
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.