first AA-native x402 stack
NERO 402 Documentation
NERO 402 is the first AA-native settlement scheme for the x402 V2 HTTP payment protocol. ERC-4337 smart-contract wallets pay any API directly over HTTP 402, and a paymaster sponsors gas — so an AI agent settles in stablecoins while holding none of the chain's native token. This site is the developer reference: SDKs, concept guides, the facilitator API, and the protocol spec.
Where to start
Quickstart for agents
Pay any x402-gated endpoint from a browser tab or a Node script in 30 lines.
Quickstart for merchants
Wrap an existing Express, Hono, Fastify, or Next.js handler with a payment gate.
Install the SDK
Five packages under @nerochain/x402-*. Pick what you need.
The aa-native scheme
What changes from x402's exact scheme, and why ERC-4337 accounts need a separate one.
Paymaster sponsorship
How agents pay APIs without holding the chain's native gas asset.
How it compares
NERO 402 vs x402 exact, Stripe, and other agent-payment options.
What is NERO 402
The upstream x402 exact scheme settles through EIP-3009 transferWithAuthorization, which only EOAs can sign. On NERO Chain every wallet is a smart-contract wallet, so exact is effectively unusable. NERO 402 contributes a second scheme — aa-native — that closes that gap: the wallet signs an ERC-4337 UserOperation whose call data invokes an on-chain settlement contract.
The wire envelope is the canonical x402 V2 payload; only the inner payload differs per scheme, so unmodified upstream @x402/fetch clients interoperate with the reference facilitator out of the box. Replay protection is on-chain, gas is paymaster-sponsored, and a single settlement contract serves every merchant.
Built for autonomous agents
Every machine-readable surface an AI agent needs is published at a predictable URL on this domain.
llms.txt
Navigation index of the docs for LLMs, with links to every key resource.
llms-full.txt
The entire documentation set bundled into one markdown file.
OpenAPI spec
The facilitator API (/verify, /settle, /supported) as OpenAPI 3.1.
Glossary
Ground-truth definitions of every NERO 402, x402, and ERC-4337 term, as schema.org DefinedTermSet.
MCP server
Model Context Protocol endpoint exposing docs search, protocol facts, and define_term as tools.
MCP integration guide
Wrap NERO 402 paid calls behind an MCP server so an LLM can spend through a tool.
auth.md
How an agent obtains credentials and authenticates a payment, step by step.
Frequently asked
What is NERO 402?
NERO 402 is the first production implementation of an AA-native settlement scheme for the x402 V2 HTTP payment protocol. It lets ERC-4337 smart-contract wallets pay merchants directly over HTTP 402, while a paymaster sponsors gas so the agent never needs the chain's native asset.
How does the aa-native scheme differ from x402's exact scheme?
The exact scheme requires the paying account to be an EOA that signs EIP-3009 typed data, so smart-contract wallets cannot use it. The aa-native scheme has the wallet sign an ERC-4337 UserOperation that calls a settlement contract, so any standard ERC-20 works and gas is paymaster-sponsored. The wire envelope is identical; only the inner payload differs.
Does an agent need a NERO native balance to pay?
No, for aa-native payments. The paymaster sponsors UserOperation gas, including the wallet's first-time deployment. The agent only ever holds the settlement asset such as USDT, USDC, or testnet DEMO-USDT.
What does NERO 402 cost to use and is there a test environment?
The SDK and reference facilitator are open source and free. Payments themselves are the merchant's per-call price in a stablecoin. A full sandbox runs on NERO Chain testnet (eip155:689) with DEMO-USDT that self-faucets via a public mint(), so agents can complete the entire flow without real funds.
What chains and tokens are supported?
NERO Chain mainnet (eip155:1689) with USDT, USDC.e, and USDC.arb, and NERO Chain testnet (eip155:689) with DEMO-USDT. The scheme itself is chain-agnostic; any chain with an ERC-4337 stack can host a settlement contract.
More in the full FAQ.