Error Handling

Module 4 · Section 7 of 9

Error Handling

Don’t let errors crash your server silently. Claude will see a generic failure and have no idea why. Be explicit:

server.setRequestHandler(CallToolRequestSchema, async (request) => {
  const toolName = request.params.name;

  if (toolName === "get_events") {
    const { start_date, end_date } = request.params.arguments as {
      start_date: string;
      end_date: string;
    };

    if (!start_date || !end_date) {
      return {
        content: [{ type: "text", text: "Error: start_date and end_date are required" }],
        isError: true,
      };
    }

    try {
      const events = await fetchEvents(start_date, end_date);
      return { content: [{ type: "text", text: events }] };
    } catch (error) {
      return {
        content: [{ type: "text", text: `Failed to fetch events: ${error}` }],
        isError: true,
      };
    }
  }

  throw new Error(`Unknown tool: ${toolName}`);
});

The isError: true flag tells Claude the call failed so it can respond appropriately — retry with different parameters, tell the user something went wrong, or try an alternative approach.