Fix error classification using __cause__ instead of raised exception type

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
2026-08-09 15:19:10 +02:00 · 2026-03-27 18:31:05 -05:00
1 changed files with 1 additions and 1 deletions
--- a/src/fastmcp/server/middleware/error_handling.py
+++ b/src/fastmcp/server/middleware/error_handling.py
@ -89,7 +89,7 @@ class ErrorHandlingMiddleware(Middleware):
            return error

        # Map common exceptions to appropriate MCP error codes
-        error_type = type(error.__cause__) if error.__cause__ else type(error)
+        error_type = type(error)

        if error_type in (ValueError, TypeError):
            return McpError(