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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Invalid method names return error code -32602 instead of -32601","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\n**How to reproduce:**\n```bash\necho '{\"jsonrpc\":\"2.0\",\"method\":\"invalid/method\",\"id\":1,\"params\":{}}' | your-mcp-server\n```\n\n**Expected result:**\n```json\n{\"jsonrpc\":\"2.0\",\"id\":1,\"error\":{\"code\":-32601,\"message\":\"Method not found\"}}\n```\n\n**Actual result:**\n```json\n{\"jsonrpc\":\"2.0\",\"id\":1,\"error\":{\"code\":-32602,\"message\":\"Invalid request parameters\",\"data\":\"\"}}\n```\n\nThe issue appears to occur because request validation in `mcp/shared/session.py` (lines 360-375) catches the validation exception and returns `-32602` before the proper method-not-found handler in `mcp/server/lowlevel/server.py` (lines 716-718) can be reached.\n\n### Example Code\n\n```Python\n\n```\n\n### Python \u0026 MCP Python SDK\n\n```Text\n**Environment:**\n- Python SDK version: `1.2.0`\n- Python version: `3.12`\n- Platform: macOS\n```","author":{"url":"https://github.com/corv89","@type":"Person","name":"corv89"},"datePublished":"2025-10-31T09:28:08.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/1561/python-sdk/issues/1561"}