--- layout: default ---

Prefer

IANA permanent request RFC 7240 reached by regulation 2 spellings

Declared by 37 providers across 642 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 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.

Preferprefer

Reached by regulation

Basis: mandated. The law, or a technical standard the law makes binding, names this header. Visible in a published contract, which is what is counted here.

cms-interoperability-prior-authorization 21st-century-cures-act

Carried by the fhir-bulk-data standard.

The registry

Status	permanent
Reference	RFC 7240: Prefer Header for HTTP

Providers declaring it (37)

adp advancedmd anyapi aptible athenahealth cadasto cdk-global cms cms-gov cognite ehrbase gc-ai gonitro insforge intersight jefferson-health microsoft-azure microsoft-dynamics-365 microsoft-dynamics-365-sales microsoft-power-apps morningstar nextgen-healthcare openehr oracle-weblogic paypal postman quinyx refinitiv replicate resemble-ai specterops supabase temple-health vastdata visier vitagroup wmo

Explore

All headers Async & Long-Running 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=prefer&limit=10"

Everything under a tag

curl "https://apis.io/api/v1/tags/prefer"

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

Get an API key

Free tier, no form to fill in. Signing in shares your email address with us — we store it to create your key and to recognise you if you sign in with another provider. See our Privacy Policy and Terms.

GitHub Google LinkedIn

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