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MCP JSON-RPC Error Codes

MCP uses JSON-RPC 2.0 error codes. These codes appear in error response objects from MCP servers. Standard JSON-RPC codes (-32700 to -32603) cover protocol-level failures. The most common in practice is -32602 Invalid Params when tool arguments don't match the inputSchema.

CodeName & Description
-32700

Parse Error

JSON-RPC parse error (-32700) means the server received a message it could not parse as valid JSON.

-32600

Invalid Request

JSON-RPC invalid request (-32600) means the received JSON is valid but does not conform to the JSON-RPC 2.

-32601

Method Not Found

JSON-RPC method not found (-32601) means the requested method does not exist on this server.

-32602

Invalid Params

JSON-RPC invalid params (-32602) means the method was found but the provided parameters are invalid.

-32603

Internal Error

JSON-RPC internal error (-32603) means the server encountered an unexpected internal failure.