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key

de facto — unregistered request 3 spellings

Declared by 44 providers across 324 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 (44)

abuseipdb activecampaign arduino beeceptor boom-ai builtwith cilium cloudrf controlup emailrep engineering-platform enphase-energy frontline gemini gleap greynoise holded ilert kibana knock-app komerce kong landmark-information leap leapfrog-power lilt lytics meteosource-air-quality-data-api mockaroo okta ordnance-survey ordway pagerduty postman red-hat suprsend systran tenable therundown tickitto uniform upwind viam what3words

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All headers Authentication Guidance on headers.apievangelist.com