SEP-2243: HTTP Header Standardization for Streamable HTTP Transport

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
68/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
java
Domain
api

Research direction

Start at the Java SDK's streamable HTTP transport client and trace how POST requests are built. Use SEP-2243 and the request-body fields described here to determine the header values; done means applicable POST requests send Mcp-Method and Mcp-Name so servers enforcing the standard accept them.

Written by the indexing model from the issue text.

Description

area/server area/transport enhancement P1

Description

Per SEP-2243 (HTTP Standard Headers), MCP clients MUST send the following HTTP headers on POST requests:

  • Mcp-Method: Set to the JSON-RPC method value from the request body (REQUIRED on every POST)
  • Mcp-Name: Set from params.name (for tools/call, prompts/get) or params.uri (for resources/read, resources/subscribe, resources/unsubscribe) when present

Context

The cxxmcp (C++ SDK) conformance testing revealed that the official conformance test suite's reference client (TypeScript SDK) does not send these headers, making the conformance suite self-contradictory. See:

Impact

Servers that enforce SEP-2243 (reject missing Mcp-Method with HTTP 400) are incompatible with clients that don't send these headers. This affects cross-SDK interoperability.

Request

Please implement Mcp-Method and Mcp-Name header support per SEP-2243 to ensure cross-SDK compatibility.

Dominant language
Java
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Avg merge
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Merged PRs (30d)
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