How to Make Your API Agent-Discoverable with llms.txt

Description and use

APIs with llms.txt, agents.json, and openapi.json are automatically discovered by agents, pay via HTTP 402, and the SDK generates all required files.

Problem

AI agents skip APIs that lack machine-readable manifests, preventing discovery and monetization.

Outcome

Two agents discovered the API, made payments totaling $0.125, and the SDK automatically generated all required discovery files.

Workflow

• Create llms.txt with service, authentication, and payment details
• Create agents.json with Schema.org Service and Offer data
• Create openapi.json with x‑402 pricing extensions
• Deploy API with x‑402 middleware (e.g., nano‑empire‑tollbooth)
• Publish the three files at the domain root
• Agents crawl the files, discover the API, and pay via HTTP 402
• Agents retry with signed receipt and receive 200 OK

Evidence

Result: 2 agents found us organically, paid $0.125 total.

Source

The SDK generates all three discovery files automatically.

Source