fix: log exceptions in tool calls at ERROR level

[gingeekrishna]

Summary

Fixes #3266.

_handle_call_tool silently converts all exceptions into CallToolResult(is_error=True) without any server-side logging, making tool failures invisible in server logs. The existing resource and prompt handlers both call logger.exception() before handling the error — this PR applies the same pattern to tool calls.

Before: A tool raising ValueError("something went wrong") returns an is_error result to the client with no trace in server logs.

After: The same exception is logged at ERROR level (with full traceback via logger.exception) before the is_error result is returned.

Change

src/mcp/server/mcpserver/server.py — one line added in _handle_call_tool:

except Exception as e:
    logger.exception(f"Error calling tool {params.name}")  # ← added
    return CallToolResult(content=[TextContent(type="text", text=str(e))], is_error=True)

This mirrors the pattern in _handle_read_resource (line 566) and _handle_get_prompt (line 1296).

Test

Added test_call_tool_exception_is_logged_server_side to tests/interaction/mcpserver/test_tools.py. It asserts that when a tool raises an exception, a log record at ERROR level containing the tool name is emitted by mcp.server.mcpserver.server.

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}

[Copilot]

Pull request overview

Adds server-side ERROR logging for unexpected failures during tool invocation so operators can diagnose tool call issues that previously only surfaced as CallToolResult(is_error=True) to clients.

Changes:

• Log exceptions in _handle_call_tool with logger.exception(...) before returning an error result.
• Add an interaction test ensuring tool-call exceptions emit an ERROR log record containing the tool name.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/mcp/server/mcpserver/server.py	Logs exceptions raised during tool calls via logger.exception before returning an is_error tool result.
tests/interaction/mcpserver/test_tools.py	Adds a regression test asserting tool-call exceptions are logged at ERROR level on the server logger.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.