Content Negotiation

Content negotiation selects the representation that best matches a request and the server's available variants.

Use Accept, Accept-Encoding, and Accept-Language to negotiate media type, content coding, and language. Send Vary when the selected response changes with a request field.

httprepresentationscacheheader

Reference (http)

Accept: application/json
Accept-Encoding: br, gzip
Accept-Language: en-US, de;q=0.8

Use Accept, Accept-Encoding, and Accept-Language to negotiate media type, content coding, and language. Send Vary when the selected response changes with a request field.

Common mistakes

Ignoring the client's preferences or forgetting Vary, which can make a cache serve one variant to another request.

Sources

MDN HTTP Reference
IANA HTTP Field Name Registry