MCPay — Payment Layer for MCP Tool Servers

MCPay solves a critical gap in the agentic economy: 10,000+ MCP (Model Context Protocol) tool servers exist today, but developers earn $0 per call despite AI agents using their tools thousands of times daily. Traditional payment rails make this impossible. Stripe charges a $0.30 minimum fee per transaction — that is 300x the value of a $0.001 tool call. Ethereum gas costs $0.05+ per transaction — still 50x the call value. Sub-cent per-call billing was economically impossible until Arc. MCPay adds x402 Nanopayments middleware to any MCP server. When an AI agent calls a tool, MCPay intercepts the request, processes a $0.001 USDC payment via Circle Nanopayments on Arc, and only then returns the data. Developers earn per call. Agents pay per use. The MCP ecosystem becomes economically sustainable for the first time. We demonstrated this with two AI agents — a Gemini Flash agent planning a European travel itinerary and a Featherless AI agent researching global cities — both autonomously paying $0.001 USDC per tool call, generating 91 on-chain transactions in a single demo session. The margin proof is mathematical: 91 tool calls on Stripe would cost $27.30 in fees alone. On Ethereum L2 it would cost $4.55 in gas. On Arc with Circle Nanopayments the gas cost is $0.00 — Circle batches settlement, making this business model viable for the first time in history. Track 1: Per-API Monetization Engine Track 2: Agent-to-Agent Payment Loop