pay-protocol

Smart contracts for Pay -- the complete x402 payment stack for AI agents. USDC on Base.

Contracts

Contract	Role	Upgradeability
PayDirect	One-shot USDC transfers with fee deduction	Immutable
PayTab (V2/V5)	Tab lifecycle: open, charge, settle, close, top-up	Immutable
PayFee	Fee calculation and provider volume tracking	UUPS upgradeable
PayRouter	Entry point for x402 settlement and direct payments	UUPS upgradeable

Fund-holding contracts (PayDirect, PayTab) are immutable -- no proxy, no admin key, no upgrade path. USDC flows directly between agent and provider via the contract.

Security

• Immutable fund-holding contracts (no admin functions)
• CEI pattern + reentrancy guards on all state-changing functions
• maxChargePerCall enforced on-chain per tab
• Activation fee prevents dust-tab spam
• Custom errors (no require strings)
• Fuzz tests on all numeric operations
• Invariant tests on safety properties

Development

This is a Foundry project. Solidity 0.8.x with OpenZeppelin.

forge build
forge test

Deployed Addresses

Always fetch addresses at runtime from the API:

curl https://pay-skill.com/api/v1/contracts

See Contracts & Networks for details.

Part of Pay

Pay is the complete x402 payment stack -- gateway, facilitator, SDKs, CLI, and MCP server -- that lets AI agents pay for APIs with USDC on Base.

• Documentation
• Architecture
• SDK -- Python + TypeScript
• CLI -- Command-line tool
• pay-gate -- x402 payment gateway
• MCP Server -- Claude Desktop / Cursor / VS Code

License

MIT