> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fiddler.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

> Complete API reference for fiddler-langchain-js

[![npm](https://img.shields.io/npm/v/@fiddler-ai/langchain)](https://www.npmjs.com/package/@fiddler-ai/langchain)

## Overview

The `@fiddler-ai/langchain` package provides LangChain JS instrumentation
for Fiddler AI observability. It re-exports the callback handler and
instrumentor from `@fiddler-ai/langgraph` under a LangChain-branded API,
enabling automatic trace capture for LangChain applications with zero
code changes to existing chains.

```bash theme={null}
npm install @fiddler-ai/langchain
```

```typescript theme={null}
import { LangChainInstrumentor, setConversationId } from '@fiddler-ai/langchain';
```

## Components

### Core

The full LangChain JS instrumentation surface, re-exported from `@fiddler-ai/langgraph` under a LangChain-branded API. `LangChainInstrumentor` is the one-time setup and `FiddlerCallbackHandler` emits spans; the `setConversationId`, `setLlmContext`, and `addSessionAttributes` families propagate conversation, session, and retrieval context, while the remaining utilities handle message formatting and serialization.

* [addSessionAttributes](/sdk-api/langchain-js/add-session-attributes)
* [CallbackManagerModule](/sdk-api/langchain-js/callback-manager-module)
* [extractTextContent](/sdk-api/langchain-js/extract-text-content)
* [FiddlerCallbackHandler](/sdk-api/langchain-js/fiddler-callback-handler)
* [formatMessages](/sdk-api/langchain-js/format-messages)
* [getConversationId](/sdk-api/langchain-js/get-conversation-id)
* [getLlmContext](/sdk-api/langchain-js/get-llm-context)
* [getProviderFromModel](/sdk-api/langchain-js/get-provider-from-model)
* [getSessionAttributes](/sdk-api/langchain-js/get-session-attributes)
* [LangChainInstrumentor](/sdk-api/langchain-js/lang-chain-instrumentor)
* [runWithContext](/sdk-api/langchain-js/run-with-context)
* [safeStringify](/sdk-api/langchain-js/safe-stringify)
* [setConversationId](/sdk-api/langchain-js/set-conversation-id)
* [setLlmContext](/sdk-api/langchain-js/set-llm-context)
* [truncate](/sdk-api/langchain-js/truncate)