A count here is providers whose published contract declares this header — not
providers who send it. Response headers set at the edge rarely appear in an OpenAPI at all, so a low
number can measure documentation practice rather than deployment.
Spelled 2 ways
HTTP field names are case-insensitive (RFC 9110 §5.1),
so every spelling below is the same header on the wire. A contract is not the wire: generated clients key off
the string, and a developer reading two of these sees two different headers.
Signaturesignature
Reached by regulation
Basis: mandated.
The law, or a technical standard the law makes binding, names this header.
Only a credentialed caller can observe it in flight — the catalog can see a contract declare it, not a deployment honour it.
Every header here is available over the APIs.io API and to AI agents over MCP. HTTP Headers is not yet its own endpoint on the v1 API. Reach it through catalog search and the tag graph, or the MCP server.
MCP server
One button, every client — Claude, Cursor, VS Code and the rest.
https://apis.io/mcp
Tools for http headers
3 MCP tools reach this
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.
Discovery needs no key. Ratings and market analysis are Pro.
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