typescript-sdk/.changeset/content-type-media-type-validation.md

@modelcontextprotocol/sdk
patch

Validate Content-Type by its parsed media type instead of a substring match. POSTs to the Streamable HTTP server transport whose media type is not application/json are now rejected with 415 Unsupported Media Type (previously any value containing the substring passed, and valid case variants were wrongly rejected). Values with parameters (application/json; charset=utf-8, including malformed parameter sections like application/json;) continue to work, and the client's response dispatch uses the same parsed comparison.