MCP Pay Server

What is MCP Pay Server?

MCP Pay Server is a standalone implementation of the Model Context Protocol (MCP) server with HTTP+SSE transport that includes a basic pre-pay credit system using USDC deposits on Base (or Base Sepolia). It is built for developers who want to require payment for MCP tool usage.

How to use MCP Pay Server?

Install dependencies with npm install, configure a .env file in the root directory with SERVER_DEPOSIT_ADDRESS (required), BASE_RPC_URL (optional), and PORT (optional), then start with npm start. The server watches for USDC deposits and clients must include __payer and __signature in paid tool calls.

Key features of MCP Pay Server

• Exposes MCP tools, resources, and prompts
• HTTP+SSE transport for bidirectional communication
• USDC payment layer on Base or Base Sepolia
• Pre-pay credit system verified via ECDSA signatures
• Payment capabilities fetched via payments/getCapabilities method
• Built with Express, TypeScript, Viem, and Zod

Use cases of MCP Pay Server

• Requiring USDC payment for specific AI tool calls
• Monitoring on-chain USDC deposits and crediting user balances
• Enabling pre-pay credit system for MCP server access

FAQ from MCP Pay Server

What does MCP Pay Server do?

It acts as an MCP server that requires clients to pre-pay with USDC before executing certain tools, using cryptographic signature verification to authorize payments.

What are the dependencies and runtime requirements?

The server requires Node.js, npm, a configured .env file with SERVER_DEPOSIT_ADDRESS, and optionally a custom RPC URL for Base or Base Sepolia. It runs on port 3000 by default.

Where are payments and balances tracked?

Payments are tracked by monitoring USDC deposits on the Base blockchain to the configured SERVER_DEPOSIT_ADDRESS. Balances are stored in the server’s internal ledger.

What transport and authentication does the server use?

The server uses HTTP+SSE transport. Authentication for paid tools requires clients to include __payer (their Ethereum address) and __signature (ECDSA signature of the canonical request) in tool call arguments.

What are the known limits?

The cost for paid tools (e.g., greet at 0.05 USDC) is deducted only if the tool execution succeeds. Signature verification and balance check happen before execution. The balance check tool payments_getBalance is free and requires no signature.