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LangGraph.js Workflow with X402 Payment Support

This example demonstrates how to build LangGraph.js workflows that include payment nodes for accessing paid APIs using the X402 payment protocol.

Features

  • Payment Nodes: Reusable nodes for handling payments in workflows
  • Conditional Routing: Route based on payment requirements
  • Multi-Step Workflows: Access multiple paid APIs in sequence
  • State Management: Proper state handling for payment status
  • TypeScript: Full type safety with LangGraph.js

Prerequisites

  1. Express.js Server: The express-server example must be running 

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    cd ../express-server
pnpm install && pnpm run build && pnpm start

  2. Wallet with Funds: You need a Solana wallet with:

  3. SOL for transaction fees
  4. USDC tokens for payments (on devnet)

Setup

  1. Install dependencies: 

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    pnpm install

  2. Create .env file (optional): 

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    cp .env.example .env

  3. The first run will create a wallet file (wallet.json)

  4. Important: Fund this wallet with SOL and USDC on devnet
  5. Get SOL: solana airdrop 1 <ADDRESS> --url devnet
  6. Get USDC: Use a devnet faucet

Running Examples

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# Build
pnpm run build

# Run
pnpm start

# Or run in dev mode
pnpm run dev

Examples

Example 1: Simple Payment Workflow

Uses fetchWithPaymentNode for easy payment integration: - Single node handles both fetch and payment - Minimal configuration - Automatic payment handling

Example 2: Custom Workflow with Conditional Payment

Demonstrates explicit payment handling: - Separate fetch and payment nodes - Conditional routing based on payment requirements - Custom error handling

Example 3: Multi-Step Research Workflow

Shows complex multi-API workflows: - Access multiple paid APIs sequentially - Collect and aggregate results - State management across multiple steps

How It Works

Payment Flow

  1. Fetch Node: Attempts to fetch API
  2. Check Payment: Determines if payment is required (402 response)
  3. Payment Node: Creates and broadcasts payment if needed
  4. Process Node: Processes API response
  5. State Updates: Tracks payment status throughout workflow

State Management

```typescript interface PaymentState { wallet_keypair: Keypair; api_url: string; api_response?: string; payment_required?: boolean; payment_completed?: boolean; payment_error?: string; max_payment_amount?: string; }