Tracking Tool Calls

Learn how to track tool calls in your LLM agent applications

Most agent frameworks automatically track tool calls for you. If you’re using LangChain, LangGraph, Mastra, or other supported frameworks, tool calls are already being captured automatically. You only need manual instrumentation for custom tools or unsupported frameworks.

Manual Tool Tracking

If you have custom tools that aren’t automatically tracked, you can manually instrument them by setting the span type to "tool":

import { setupObservability } from "langwatch/observability/node";
import { getLangWatchTracer } from "langwatch";

setupObservability();

const tracer = getLangWatchTracer("agent-service");

const agentCall = async (query: string): Promise<string> => {
  return await tracer.withActiveSpan("AgentCall", async (span) => {
    // Your agent logic here
    const result = await myCustomTool(query);
    return result;
  });
};

const myCustomTool = async (query: string): Promise<string> => {
  return await tracer.withActiveSpan("MyCustomTool", async (span) => {
    span.setType("tool");

    // Your custom tool implementation
    const result = `Tool result for: ${query}`;
    return result;
  });
};

await agentCall("What's the weather?");

This will display the tool call with a tool icon in the trace visualization and include it in tool call analytics in the LangWatch dashboard.