# Vault402

> Vault402 is an open-source TypeScript SDK for HTTP 402 Payment Required on Robinhood Chain (an Ethereum L2 built on Arbitrum; mainnet chain ID 4663, testnet 46630). APIs use the `requirePayment()` Express middleware to charge per request. AI agents use `createAgentClient().fetch()` to pay automatically within a budget, in ETH, USDC, Robinhood Stock Tokens or any ERC-20.

Key facts:
- Two payment schemes: `transaction` (the agent sends the transfer and the server verifies the receipt) and `authorization` (the agent signs an EIP-3009 transferWithAuthorization and the server settles it and pays the gas).
- Three access models: one-time, pass (time-limited) and credits (prepaid number of calls).
- Every 402 challenge has a single-use `paymentId`, carried in the transfer calldata or as the EIP-3009 nonce, which prevents replay.
- Agents must set a budget per token (`maxPerPayment`, optional `maxTotal`) and refuse offers outside it.
- License: MIT. Package: `vault402` on npm.
- Token: Agent Vault ($AGENT), the token of the Vault402 network. ERC-20 on Robinhood Chain (chain ID 4663), total supply 1,000,000,000. Official contract: 0x1f5C3FED482AeFf409b955B3ad371678c08e91E2 (https://robinhoodchain.blockscout.com/token/0x1f5C3FED482AeFf409b955B3ad371678c08e91E2)

## Docs
- [Documentation](https://vault402.network/docs): install, networks, tokens, sellers, buyers, schemes, access models
- [Examples](https://vault402.network/examples): selling data, agent purchases, passes and credits, multi-token and Stock Token pricing, testnet
- [Protocol reference](https://github.com/CombotxTech/vault402/blob/main/INTEGRATION_GUIDE.md): wire format of the 402 challenge, X-PAYMENT and X-PAYMENT-RESPONSE headers
- [Agent install guide](https://vault402.network/install.md)

## Source
- [GitHub](https://github.com/CombotxTech/vault402)
- [npm](https://www.npmjs.com/package/vault402)