Proposal: MCP (Model Context Protocol) test profiles

[nigrosimone]

MCP servers are increasingly deployed as regular HTTP services using the Streamable HTTP transport, and many are built on the same frameworks HttpArena already ranks (Express, Fastify, Hono, FastAPI, ASP.NET, …).

None of the current profiles captures what an MCP request actually costs:

• JSON-RPC 2.0 dispatch: routing by method inside the body, id echoing, spec-defined error codes. The JSON profile serializes a payload but never dispatches on it.
• Session state: an Mcp-Session-Id header is validated on every request.
• SSE framing on POST responses: text/event-stream responses carrying one or more JSON-RPC messages. No current profile measures streamed response bodies.

gRPC covers binary RPC over HTTP/2. MCP would cover the JSON-RPC-over-HTTP side, which is where much of today's tool-calling traffic lives.

Proposed profiles

Profile	Endpoint	Response type	Measures
mcp	POST /mcp	application/json	JSON-RPC dispatch + session lookup
mcp-sse	POST /mcp-sse	text/event-stream	Same, plus SSE framing (progress + result)

[MDA2AV]

Ok, I like this.

Need to think on how we can get a load generator for this.