EVM Mechanisms

This directory contains payment mechanism implementations for EVM (Ethereum Virtual Machine) networks.

What This Exports

This package provides scheme implementations for EVM-based blockchains (Ethereum, Base, Optimism, Arbitrum, Polygon, etc.) that can be used by clients, servers, and facilitators.

Exact Payment Scheme

The exact scheme implementation enables fixed-amount payments using EIP-3009 transferWithAuthorization for USDC and compatible tokens.

Export Paths

The exact scheme is organized by role:

For Clients

Import Path:

github.com/coinbase/x402/go/mechanisms/evm/exact/client

Exports:

• NewExactEvmScheme(signer) - Creates client-side EVM exact payment mechanism
• Used for creating payment payloads that clients sign

For Servers

Import Path:

github.com/coinbase/x402/go/mechanisms/evm/exact/server

Exports:

• NewExactEvmScheme() - Creates server-side EVM exact payment mechanism
• Used for building payment requirements and parsing prices
• Supports custom money parsers via RegisterMoneyParser()

For Facilitators

Import Path:

github.com/coinbase/x402/go/mechanisms/evm/exact/facilitator

Exports:

• NewExactEvmScheme(signer) - Creates facilitator-side EVM exact payment mechanism
• Used for verifying signatures and settling payments on-chain
• Requires facilitator signer with blockchain RPC integration

Supported Networks

All EVM-compatible networks using CAIP-2 network identifiers:

• Ethereum Mainnet: eip155:1
• Base Mainnet: eip155:8453
• Base Sepolia: eip155:84532
• Optimism: eip155:10
• Arbitrum: eip155:42161
• Polygon: eip155:137
• Any other EVM chain via eip155:{chainId}

Use eip155:* wildcard to support all EVM networks.

Scheme Implementation

The exact scheme implements fixed-amount payments:

• Standard: EIP-3009 transferWithAuthorization
• Token: USDC and EIP-3009 compatible tokens
• Gas: Paid by facilitator
• Confirmation: On-chain settlement with transaction hash

Future Schemes

This directory currently contains only the exact scheme implementation. As new payment schemes are developed for EVM networks, they will be added here alongside the exact implementation:

evm/
├── exact/          - Fixed amount payments (current)
├── upto/           - Variable amount up to a limit (planned)
├── subscription/   - Recurring payments (planned)
└── batch/          - Batched payments (planned)

Each new scheme will follow the same three-role structure (client, server, facilitator).

Contributing New Schemes

We welcome contributions of new payment scheme implementations for EVM networks!

To contribute a new scheme:

1. Create directory structure: evm/{scheme_name}/client/, evm/{scheme_name}/server/, evm/{scheme_name}/facilitator/
2. Implement the required interfaces for each role
3. Add comprehensive tests
4. Document the scheme specification
5. Provide usage examples

See CONTRIBUTING.md for more details.

Related Documentation

• Mechanisms Overview - About mechanisms in general
• SVM Mechanisms - Solana implementations
• Exact Scheme Specification - EVM exact scheme spec