MCP-JSONRPC-32602 Error Troubleshooting Guide

Overview

MCP-JSONRPC-32602 is one of the most common errors in MCP tool calling. When an AI Agent calls an MCP tool with parameters that don't match the tool's schema definition, the server returns this error.

This error typically means:

• ❌ Missing required parameters
• ❌ Parameter type mismatch
• ❌ Parameter value out of range
• ❌ Incorrect parameter format

Error Response Format

When this error occurs, the MCP server returns the following standard error response structure:

{
  "jsonrpc": "2.0",
  "id": 42,
  "error": {
    "code": -32602,
    "message": "Invalid params",
    "data": {
      "param": "connection_string",
      "reason": "missing required parameter"
    }
  }
}

Common Causes and Solutions

Cause 1: Missing Required Parameters

Solution: Check the required field in the tool definition and ensure all required parameters are provided.

Cause 2: Parameter Type Mismatch

Solution: Ensure the parameter types match the tool definition.

Cause 3: Parameter Name Spelling Error

Solution: Carefully check parameter names, paying attention to case sensitivity.

Cause 4: Parameter Value Out of Range

Solution: Adjust parameter values to be within the valid range.

Reference Sources

• JSON-RPC 2.0 Specification
• MCP Error Codes - mcpevals.io
• MCP Schema Reference