Internet Assigned Numbers Authority (IANA)

IANA media types, also known as MIME types, are the standardized names for the kinds of data moving across the internet — application/json, text/html, image/png, and thousands more. The Internet Assigned Numbers Authority maintains the official registry, and the registration procedures live in RFC 6838, so that a value like application/vnd.github+json means the same thing to every client and server that reads it.

• A central registry - IANA keeps the authoritative list, so media types are discoverable and unambiguous rather than invented per-vendor.
• A type/subtype grammar - A top-level type plus a subtype, with optional +suffix (like +json or +xml) and parameters, gives structured, parseable names.
• Vendor and structured trees - The vnd. and prs. trees let organizations register their own formats without colliding with the standards tree.
• The plumbing of content negotiation - Media types are the vocabulary that Content-Type and Accept headers speak.

In real API operations, media types are how a producer and a consumer agree on what is on the wire before a single byte is parsed. They drive content negotiation, version formats through custom vnd. types, and increasingly signal to agents and tools which representation of a resource to request. Getting the media type right is one of the smallest, most overlooked decisions that determines whether a client can reliably read what an API returns.