I Built a Paid API That AI Agents Use Autonomously

Last week, Tempo and Stripe launched the Machine Payments Protocol. The idea: HTTP 402 (Payment Required) finally does something useful. An agent requests data, the server says “pay me first,” the agent pays in USDC, and the server delivers. I wanted to see how fast I could build a real paid service on top of this. Turns out, pretty fast. What I built FinSight is a financial portfolio analytics API. AI agents send a portfolio (a list of assets with weights, returns, and volatility numbers), pay a small amount in USDC per call, and get structured analysis back.