@fail-kit/langchain

v1.5.0 - LangChain.js adapter for F.A.I.L. Kit

Drop-in adapter for integrating LangChain.js agents with the F.A.I.L. Kit audit framework.

Installation

npm install @fail-kit/langchain
# or
yarn add @fail-kit/langchain
# or
pnpm add @fail-kit/langchain

Quick Start

import express from 'express';
import { AgentExecutor } from 'langchain/agents';
import {
  createFailKitRouter,
  ReceiptGeneratingTool
} from '@fail-kit/langchain';

const app = express();
app.use(express.json());

// Define tools with automatic receipt generation
class EmailTool extends ReceiptGeneratingTool {
  name = 'email_sender';
  description = 'Send an email';
  
  async _execute(input: { to: string; subject: string; body: string }) {
    await sendEmail(input.to, input.subject, input.body);
    return { status: 'sent', message_id: 'msg_123' };
  }
}

// Create agent
const tools = [new EmailTool()];
const agentExecutor = new AgentExecutor({ agent, tools });

// Add F.A.I.L. Kit endpoint
app.use('/eval', createFailKitRouter(agentExecutor));

app.listen(8000);

Features

• ✅ Automatic receipt generation from tool executions
• ✅ Full RECEIPT_SCHEMA.json compliance
• ✅ TypeScript support with full type definitions
• ✅ Custom metadata in receipts
• ✅ Error handling with failure receipts
• ✅ SHA256 hashing for verification
• ✅ Works with LangGraph

API Reference

createFailKitRouter(agentExecutor, config?)

Creates an Express router with the /run endpoint.

Parameters:

• agentExecutor: LangChain AgentExecutor instance
• config: Optional FailKitConfig

Returns: Express Router

ReceiptGeneratingTool

Base class for tools with automatic receipt generation.

Methods:

• _execute(input: any): Override with your tool logic
• getReceipts(): Get all receipts
• clearReceipts(): Clear receipt history

extractReceiptsFromAgentExecutor(executor, result, config?)

Extract receipts from AgentExecutor intermediate steps.

wrapToolWithReceipts(tool)

Wrap a legacy LangChain tool to generate receipts.

Examples

See examples/langchain-javascript/ for a complete working example.

Testing

npm test

Related

• @fail-kit/core - Core receipt generation library
• F.A.I.L. Kit CLI - Command-line audit tool
• F.A.I.L. Kit VS Code Extension - IDE integration

License

MIT License - See LICENSE