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This module provides automatic instrumentation for LangChain.js, more specifically, the @langchain/core module. which may be used in conjunction with @opentelemetry/sdk-trace-node.

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Install

npm install --save @arizeai/openinference-instrumentation-langchain \
  @arizeai/phoenix-otel

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Setup

To load the LangChain instrumentation, manually instrument the @langchain/core/callbacks/manager module. The callbacks manager must be manually instrumented due to the non-traditional module structure in @langchain/core. 
import { register } from "@arizeai/phoenix-otel";
import { LangChainInstrumentation } from "@arizeai/openinference-instrumentation-langchain";
import * as CallbackManagerModule from "@langchain/core/callbacks/manager";

const provider = register({
  projectName: "langchain-app",
});

const lcInstrumentation = new LangChainInstrumentation();
// LangChain must be manually instrumented as it doesn't have 
// a traditional module structure
lcInstrumentation.manuallyInstrument(CallbackManagerModule);
Once instrumentation is setup, your agent will automatically export traces to Phoenix. 
import * as z from "zod";
// npm install @langchain/anthropic to call the model
import { createAgent, tool } from "langchain";

const getWeather = tool(
  ({ city }) => `It's always sunny in ${city}!`,
  {
    name: "get_weather",
    description: "Get the weather for a given city",
    schema: z.object({
      city: z.string(),
    }),
  },
);

const agent = createAgent({
  model: "claude-sonnet-4-5-20250929",
  tools: [getWeather],
});

console.log(
  await agent.invoke({
    messages: [{ role: "user", content: "What's the weather in Tokyo?" }],
  })
);

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Support

Instrumentation version >=4.0.0 supports LangChain 1.0 and above. If you are still using older versions of LangChain we recommend using the dedicated package @arizeai/openinference-instrumentation-langchain-v0 which will receive patches for the older versions.

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