Internal Error
JSON-RPC internal error (-32603) means the server encountered an unexpected internal failure. The request was valid and the method exists, but the server could not process it due to an unhandled exception, resource exhaustion, or implementation bug.
Code
-32603
Decimal
-32603
Standard
JSON-RPC 2.0
Description
Internal Error is the catch-all for server-side failures that are not the client's fault. In MCP tool execution, this typically means the tool's implementation threw an unhandled exception, a downstream API call failed unexpectedly, or the server ran out of memory. Note the distinction from tool execution errors: if a tool executes but returns an error result (e.g., API returned 404), the server should return a 200 tools/call result with isError: true. The -32603 code is for infrastructure-level failures where the tool could not even attempt execution.
Common Causes
- –Unhandled exception in tool implementation
- –Server ran out of memory during execution
- –Database connection failed during resources/read
- –Subprocess spawned by a tool crashed unexpectedly
- –Bug in the MCP server framework itself