Concepts and guides for the agent economy

x402 turns HTTP 402 Payment Required into a working settlement layer for autonomous agents. Here is the handshake, the EIP-3009 USDC authorization, and why it is the wire format for agentic commerce.

A step-by-step guide to wrapping any HTTP endpoint with x402: pricing, the 402 response, verification, settlement, free tiers, and listing it in an agent API marketplace so autonomous agents can discover and pay for it.

API keys, monthly invoices, and Stripe Checkout were designed for humans. Here is a head-to-head comparison with per-call x402 settlement, and when each model still wins.

Autonomous agents do not browse marketing sites. Here is the discovery stack — llms.txt, /.well-known/x402, OpenAPI, MCP, and Markdown twins — that lets an agent find, price-check, and call a machine-payable API without a human in the loop.

A practical agent-first guide to enforcing spend policy before signing an x402 payment: validating 402 accepts[], comparing network, asset, payee, and amount against an allowlist, and recording debits only from successful payment receipts.

How an AI agent uses the Model Context Protocol to discover machine-payable APIs, read live x402 payment requirements, and call endpoints that settle in USDC on Base — without accounts or API keys.

Prove your agent can complete the x402 handshake with testnet USDC and mock responses before spending real Base mainnet USDC. Query param, assets, facilitator, and a checklist for promoting to production.

Marketplace for AI Agents gives every agent identity 3 free calls across all endpoints before x402 payment kicks in. Here is how identity is scoped, how to read X-Free-Calls-Remaining, and how to graduate to paid USDC calls without surprise 402s.

When a user asks an agent for YouTube captions or a video transcript, call a machine-payable transcript endpoint that returns JSON segments — no YouTube Data API key, no Google Cloud project, settlement via x402 USDC on Base after three free evaluation calls.