Invalid Params
JSON-RPC invalid params (-32602) means the method was found but the provided parameters are invalid. In MCP tools/call this means the arguments object does not match the tool's inputSchema – missing required fields, wrong types, or extra fields not in the schema.
Code
-32602
Decimal
-32602
Standard
JSON-RPC 2.0
Description
Invalid Params is the most common MCP error in practice. When calling tools/call, the arguments object must match the JSON Schema defined in the tool's inputSchema. If a required property is missing, a property has the wrong type, or an enum value is not in the allowed list, the server returns -32602. MCP clients should validate arguments against the tool's inputSchema before sending. The error response should include a data field explaining which parameter is invalid.
Common Causes
- –tools/call arguments missing a required property from inputSchema
- –Argument value has wrong type (string where number expected)
- –Enum argument not in the allowed values list
- –resources/read uri parameter is not a valid URI format
- –prompts/get arguments missing a required argument defined in the prompt