Request metadata

Put protocol context on every request.

For MCP protocol revision 2026-07-28

The new stateless model cannot rely on facts remembered from initialization. Each JSON-RPC request therefore includes a params._meta object with namespaced MCP keys.

Minimum metadata

"_meta": {
  "io.modelcontextprotocol/protocolVersion": "2026-07-28",
  "io.modelcontextprotocol/clientCapabilities": {}
}

Both keys are required. An empty capability object means no optional client capability is available for this call. Servers must not infer capabilities from an earlier request.

Recommended client identity

"io.modelcontextprotocol/clientInfo": {
  "name": "example-client",
  "version": "1.0.0"
}

Identity helps display, logging and debugging, but it is self-reported. Never use it as proof of identity or an authorization decision.

HTTP agreement

The body protocol version must match MCP-Protocol-Version. A disagreement is a header mismatch and should produce standard error -32020. This explicit duplication allows HTTP infrastructure to route safely without parsing a full body while retaining protocol-level verification.

Validate a sample

Use the MCP request metadata checker to catch missing keys and mismatches before sending a real request.