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x-idempotency-key

de facto — unregistered request reached by regulation 3 spellings

Declared by 52 providers across 815 published specification files in the APIs.io network.

What this header is for, and how to use it →

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 3 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.

x-idempotency-keyX-Idempotency-KeyxIdempotencyKey

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.

cma-open-banking-order

Carried by the uk-open-banking-standard standard.

Providers declaring it (52)

aldermore allica-bank appdirect ardent bank-of-ireland-uk bank-of-scotland barclays bindbee bread-financial c-hoare-and-co cashfree cashplus chase-uk commerce-coinbase coutts coventry-building-society cover-genius crossmint customers-bank cynergy-bank danske-bank-uk first-direct float-financial flutterwave gb-bank hampden-and-co here investec kroo light lloyds-banking-group monument-bank nala natwest onsi open-banking-uk paragon-bank primer recognise-bank revolut runa santander-uk secure-trust-bank shawbrook-bank slash socotra tandem-bank vanquis-banking-group versusgame vital-io yorkshire-building-society zopa

Explore

All headers Idempotency & Reliability Guidance on headers.apievangelist.com

Work with this as data

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.

All 92 tools →

Call it yourself

curl for this page

Search the catalog

curl "https://apis.io/api/v1/search?q=x-idempotency-key&limit=10"

Everything under a tag

curl "https://apis.io/api/v1/tags/x-idempotency-key"

Discovery needs no key. Ratings and market analysis are Pro.

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