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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Invalid JSON-RPC envelope errors are not correlated with the original request id","articleBody":"### Initial Checks\n\n- [x] I confirm that I'm using the latest version of MCP Python SDK\n- [x] I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue\n\n### Description\n\nAfter a normal initialization flow, several id-bearing JSON-RPC messages that are syntactically valid JSON but invalid JSON-RPC request envelopes are not correlated back to the original request id.\n\nThis is not meant to require implementations to recover an id after every low-level parse/deserialization failure. The narrower concern is that these payloads are parsed far enough to produce request-specific validation errors, while the original top-level id is still present in the payload. Preserving that id where feasible would make the error response easier for clients to correlate.\n\n\nThe tested inputs were:\n\n| Case                    | Request                                                | Validation detail                                       |\n| ----------------------- | ------------------------------------------------------ | ------------------------------------------------------- |\n| wrong `jsonrpc` version | `{\"jsonrpc\":\"1.0\",\"id\":3,\"method\":\"ping\",\"params\":{}}` | `JSONRPCRequest.jsonrpc`: value should be `\"2.0\"`       |\n| missing `jsonrpc` field | `{\"id\":4,\"method\":\"ping\",\"params\":{}}`                 | `JSONRPCRequest.jsonrpc`: field required                |\n| `method` as number      | `{\"jsonrpc\":\"2.0\",\"id\":8,\"method\":12345,\"params\":{}}`  | `JSONRPCRequest.method`: input should be a valid string |\n\nFor all three envelope-invalid inputs, I would expect `-32600 Invalid Request` or `-32602` error response that can be correlated to the original request where possible.\n\nObserved behavior was consistent by transport:\n\n- **stdio:** The server emits a `notifications/message` log notification with `level:\"error\"` and `data:\"Internal Server Error\"`, but no JSON-RPC error response is sent for the original request `id`. A follow-up `ping` succeeds.\n- **Streamable HTTP:** The server returns HTTP 400 with a JSON-RPC error response using `id:\"server-error\"` and `code:-32602`, rather than the original request `id`. A follow-up `ping` succeeds over SSE.\n\n### Example Code\n\n```Python\n\"\"\"\nWith a Python SDK MCP server running over stdio or Streamable HTTP,\ncomplete a normal initialization flow, then send these requests in isolation.\n\"\"\"\n\nrequests = [\n    # Wrong JSON-RPC version: valid JSON, invalid JSON-RPC envelope.\n    {\"jsonrpc\": \"1.0\", \"id\": 3, \"method\": \"ping\", \"params\": {}},\n\n    # Missing jsonrpc field: valid JSON, invalid JSON-RPC envelope.\n    {\"id\": 4, \"method\": \"ping\", \"params\": {}},\n\n    # method is not a string: valid JSON, invalid JSON-RPC envelope.\n    {\"jsonrpc\": \"2.0\", \"id\": 8, \"method\": 12345, \"params\": {}},\n]\n```\n\n### Python \u0026 MCP Python SDK\n\n```Text\n* Python: `3.12.3`\n* MCP Python SDK stable release: `v1.27.2` (`62137874ff26dd74d2fea80ff528a7fd9ca7a5e7`)\n* Transports: stdio and Streamable HTTP\n```","author":{"url":"https://github.com/cclabadmin","@type":"Person","name":"cclabadmin"},"datePublished":"2026-06-12T11:49:58.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/2848/python-sdk/issues/2848"}