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@prefactor/packages/langchain

Prefactor TypeScript SDK

Prefactor TypeScript SDK / @prefactor/packages/langchain

@prefactor/packages/langchain

LangChain adapter package exposing Prefactor initialization helpers and middleware.

`@prefactor/langchain` overview

@prefactor/langchain adds Prefactor tracing to LangChain middleware so agent, model, chain, and tool activity is captured automatically.

The package initializes once with init, then captures model and tool traces through LangChain middleware hooks. It also exposes withSpan for custom orchestration spans and getTracer for advanced instrumentation patterns.

Quick start: initialize and attach middleware

import { init } from '@prefactor/langchain';
import { createAgent } from 'langchain';

const prefactor = init({
  transportType: 'http',
  httpConfig: {
    apiUrl: 'https://api.prefactor.ai',
    apiToken: process.env.PREFACTOR_API_TOKEN!,
    agentIdentifier: 'support-bot-v1',
  },
});

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

Example: trace custom logic

import { withSpan } from '@prefactor/langchain';

await withSpan(
  {
    name: 'rank-documents',
    spanType: 'langchain:chain',
    inputs: { count: 12 },
  },
  async () => {
    // your custom chain logic
  }
);

Functions

Classes

PrefactorMiddleware