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Authentication

key

de facto — unregistered request 3 spellings

Declared by 52 providers across 442 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.

keyKeyKEY

Providers declaring it (52)

abuseipdb activecampaign arduino beeceptor boom-ai builtwith carsxe cilium cisco-ise cloudrf controlup elk-stack emailrep engineering-platform enphase frontline gameball gemini gleap greynoise holded ilert integration-os kibana knock-app komerce kong landmark-information leap lilt meteosource-air-quality-data-api mockaroo offendersearch offendersearch-api okta ordnance-survey ordway pagerduty pagesnap postman red-hat sigma-computing sk-telecom suprsend systran tenable therundown tickitto uniform upwind viam what3words

Explore

All headers Authentication 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=key&limit=10"
Everything under a tag 
curl "https://apis.io/api/v1/tags/key"

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

Get an API key

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A second provider on the same verified email joins the account you already have.