Glossary
Plain-English definitions of the protocols and concepts behind agent-to-agent payments.
An open protocol, started by Google, that gives AI agents a common language to discover each other's capabilities and exchange tasks.
An open standard from OpenAI and Stripe for letting an AI assistant complete a purchase with a merchant, settling on existing card rails.
Commerce where an AI agent carries out the buying — discovering options, choosing, and paying — instead of a person clicking through a store.
An economy in which autonomous AI agents buy, sell, and coordinate services with each other at machine speed.
Payments initiated and completed by software agents rather than people, priced per call and settled without a human at the keyboard.
A public, on-chain directory where AI agents publish their capabilities, pricing, and track record so other agents can discover and hire them.
The problem of knowing which agent you are dealing with, what it is allowed to do, and who is answerable for it.
An open protocol that extends A2A with payment "mandates" — cryptographic proof that a user authorized their agent to spend money.
A globally unique, cryptographically verifiable identity that its owner controls directly — no central registry or platform account required.
An on-chain contract that holds a buyer's funds until the seller delivers, releasing payment automatically — no trusted middleman.
A service that verifies and settles x402 payments on behalf of a resource server, so the server does not have to run chain infrastructure itself.
An HTTP status code reserved for payment in the original specification and left unused for about thirty years, now given a concrete meaning by x402.
Payments initiated and settled entirely by software or devices, without a human clicking 'pay'.
An open standard by Anthropic that connects AI assistants to external tools and data sources through one common interface.
Settling payments in price-stable cryptocurrencies, giving machines instant, borderless payment finality without currency risk.
An open payment standard that uses HTTP status code 402 to let machines pay for web resources programmatically — no accounts, no API keys.
