Content negotiation lets one URL represent the same underlying resource in formats suited to different clients. A browser may receive HTML, while a compatible tool may request compact Markdown or structured data by sending an accepted media type or another supported preference.
Servers should make negotiated behavior deterministic and cache-safe. Responses need the correct content type and variation headers, and every representation should preserve the same authoritative meaning. A client that does not request a special format should continue to receive the normal human-facing page.
ELI5
Content negotiation is how a web client asks a server for the most suitable version of the same resource. The client states formats or languages it can accept, and the server chooses an available match.
For example, a person opening a page may receive HTML, while an AI tool requesting the same address may receive Markdown. The server should label the response correctly, keep each version consistent and tell caches which request details can change the result.
