How to Make Your FastAPI App Discoverable by AI Agents

Description and use

FastAPI app becomes discoverable by AI agents by adding llms.txt, agents.json, implementing x402 payment, and offering a free tier.

Problem

FastAPI apps are invisible to AI agents because they lack machine‑readable discovery files and programmatic payment support.

Outcome

The API becomes discoverable by AI agents, gains programmatic payment, and attracts usage through a free tier.

Workflow

• Create /llms.txt with service description and pricing
• Create /agents.json with Schema.org Service entries
• Add x402 middleware to protected endpoints
• Register API with Smithery.ai and Glama.ai registries
• Set up proof chain for reliability verification
• Offer free tier (5 calls/day/IP) to attract agents
• Add x402 payment after volume justifies it

Evidence

Agents don't browse Google or read your landing page. They crawl specific machine-readable files that tell them what your API does, what it costs, and how to pay you.

Source

Agents won't fill out signup forms. They need to pay programmatically via the x402 protocol (HTTP 402 + USDC on Base).

Source