Debug-MCP

Instructions

Implementation Reference

• src/mcp_debug_tool/server.py:611-666 (handler)

  The primary handler function for the 'sessions_step_over' MCP tool. It validates the sessionId argument, delegates to SessionManager.step_over_async, serializes the response to JSON, and returns it as TextContent. Handles SessionNotFound and general exceptions by returning error responses.
  async def _handle_sessions_step_over(self, arguments: dict) -> list[TextContent]: """ Handler for sessions_step_over tool. Steps over the current line. """ try: session_id = arguments.get("sessionId") if not session_id: return [ TextContent( type="text", text=json.dumps({ "error": { "type": "ValueError", "message": "sessionId is required", } }), ) ] response = await self.session_manager.step_over_async(session_id) result = response.model_dump() return [ TextContent( type="text", text=json.dumps(result), ) ] except KeyError as e: return [ TextContent( type="text", text=json.dumps({ "error": { "type": "SessionNotFound", "message": str(e), } }), ) ] except Exception as e: logger.exception("Error in step_over") return [ TextContent( type="text", text=json.dumps({ "error": { "type": type(e).__name__, "message": str(e), } }), ) ]
• src/mcp_debug_tool/server.py:176-189 (schema)

  The schema definition for the 'sessions_step_over' tool, registered via list_tools(). Specifies the tool name, description, and input schema requiring a 'sessionId' string.
  Tool( name="sessions_step_over", description="Step over the current line (requires active breakpoint)", inputSchema={ "type": "object", "properties": { "sessionId": { "type": "string", "description": "The debug session ID", }, }, "required": ["sessionId"], }, ),
• src/mcp_debug_tool/server.py:222-223 (registration)

  The dispatch registration in the call_tool handler that routes 'sessions_step_over' calls to the specific _handle_sessions_step_over method.
  elif name == "sessions_step_over": return await self._handle_sessions_step_over(arguments)
• src/mcp_debug_tool/sessions.py:767-842 (helper)

  Supporting method in SessionManager that implements the step-over logic using the DAP wrapper. Checks prerequisites (DAP enabled, paused state), performs the step_over via dap_wrapper, updates session state, and returns BreakpointResponse.
  def step_over(self, session_id: str) -> BreakpointResponse: """ Step over the current line (DAP only). Args: session_id: Session ID Returns: BreakpointResponse with new location and variables Raises: KeyError: If session not found ValueError: If session is not using DAP """ session = self.get_session(session_id) if not session.use_dap: return BreakpointResponse( hit=False, completed=False, error=ExecutionError( type="NotImplementedError", message="Step operations require DAP integration (set useDap=true when creating session)", ), ) if not session.dap_wrapper: return BreakpointResponse( hit=False, completed=False, error=ExecutionError( type="SessionError", message="DAP session not initialized", ), ) if session.status != SessionStatus.PAUSED: return BreakpointResponse( hit=False, completed=False, error=ExecutionError( type="InvalidStateError", message=f"Cannot step from state: {session.status}. Must be PAUSED.", ), ) session.update_status(SessionStatus.RUNNING) with Timer() as timer: try: response = session.dap_wrapper.step_over(timeout=DEFAULT_TIMEOUT_SECONDS) # Update session state if response.hit: session.update_status(SessionStatus.PAUSED) if response.frameInfo: session.update_breakpoint(response.frameInfo.file, response.frameInfo.line) elif response.completed: session.update_status(SessionStatus.COMPLETED) elif response.error: session.update_status(SessionStatus.ERROR) session.update_timings(timer.elapsed_ms) return response except Exception as e: session.update_status(SessionStatus.ERROR) return BreakpointResponse( hit=False, completed=False, error=ExecutionError( type=type(e).__name__, message=str(e), ), )
• src/mcp_debug_tool/sessions.py:982-988 (helper)

  Async wrapper that enables the synchronous step_over method to be called awaitably from the MCP server handler.
  async def step_over_async(self, session_id: str) -> BreakpointResponse: """ Async wrapper for step_over. Runs the synchronous step_over in a thread pool to avoid blocking. """ return await asyncio.to_thread(self.step_over, session_id)