mcp-pay-server
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MCP Pay Server is a standalone implementation of the Model Context Protocol (MCP) server with HTTP+SSE transport, including a basic pre-pay credit system.
MCP Pay Server
A standalone implementation of the Model Context Protocol (MCP) server with HTTP+SSE transport, including a basic pre-pay credit system.
Features
- Exposes MCP tools, resources, and prompts
- Supports HTTP+SSE for bidirectional communication
- Implements a simple payment layer using USDC deposits on Base (or Base Sepolia)
- Built with Express, TypeScript, Viem, and Zod
Setup
-
Install dependencies:
npm install -
Configure Environment Variables: Create a
.envfile in the root directory (mcp-pay-server/.env) with the following:# Required: Public address of the wallet the server will watch for USDC deposits SERVER_DEPOSIT_ADDRESS=0xYourServerWalletPublicAddress # Optional: RPC URL for Base or Base Sepolia (defaults provided) # BASE_RPC_URL=https://your-base-rpc-url # Optional: Port for the server (defaults to 3000) # PORT=3001SERVER_DEPOSIT_ADDRESS: The public0x...address the server should monitor for incoming USDC deposits.BASE_RPC_URL: The RPC endpoint for interacting with the Base blockchain (mainnet or Sepolia).PORT: The port the HTTP server will listen on.
Usage
Start the server:
npm start
This will start the MCP server and begin watching for USDC deposits to the configured SERVER_DEPOSIT_ADDRESS.
Payment System Overview
This server uses a pre-pay credit system verified via cryptographic signatures. Clients fetch the payment capabilities separately after connecting.
- Connect: Client connects to the server.
- Fetch Capabilities: Client calls the
payments/getCapabilitiesmethod to receive:- The URI of the resource providing deposit information (e.g.,
mcp-pay://server/payment/info). - The name of the tool used for checking balances (e.g.,
payments_getBalance). - A list of tools that require payment and their associated cost (as strings).
- The URI of the resource providing deposit information (e.g.,
- Deposit Info: Clients read the deposit info resource (URI obtained from capabilities) to get the server's USDC deposit address.
- Credit: Clients send USDC (on the configured network) to the deposit address. The server monitors this address and credits the sender's account in its internal ledger.
- Paid Tool Usage: When a client calls a tool identified as paid in the capabilities:
- It must include
__payer(its0x...address) and__signature(ECDSA signature of the canonical request) in theparams.arguments. - The server's central middleware verifies the signature and checks the payer's balance against the tool's cost before executing the tool logic.
- If verification succeeds, the tool executes. If the tool execution is successful, the cost is deducted from the payer's balance.
- It must include
- Balance Check: Clients use the balance check tool (name obtained from capabilities) with their
payerAddressas an argument. This tool does not require a signature.
Available Endpoints
POST /mcp- For client requests to the server (requiresmcp-session-idheader). Handles general MCP methods andpayments/getCapabilities.GET /mcp- For SSE (Server-Sent Events) stream (requiresmcp-session-idheader).
Payment Capabilities (Exposed via payments/getCapabilities)
- Deposit Info Resource URI:
mcp-pay://server/payment/info(by default) - Balance Check Tool:
payments_getBalance(by default) - Paid Tools (Example):
greet: 0.05 USDC (by default)- (Others can be configured)
Available Tools
greet: A simple greeting tool (Requires payment by default).payments_getBalance: Returns the credit balance for the calling wallet (Free).
Available Resources
mcp-pay://server/payment/info: Returns the server's deposit address.
Development
Build the TypeScript code:
npm run build
