agent
An agent is software that acts for somebody and can pay for what it uses. The word is the sector's, not the specification's. x402 calls the paying party the client, and defines it by what it does in the exchange rather than by what kind of software it is.
x402's own repository names roles. Its client is the entity wanting to pay for a resource; its resource server is the HTTP server providing an API or other resource to that client; its facilitator handles verification and execution of payments. Nothing in those definitions requires the client to be autonomous software, and nothing excludes it.
Other specifications name the role, and the differences are load-bearing. AP2 defines a shopping agent that performs product discovery, builds the checkout and executes the purchase. It puts the capture of a person's informed consent on a separate role, so in that model the agent is not the party that consents. The Model Context Protocol calls the connecting party the AI application, and standardises how such applications reach external systems.
The practical reading is that the word describes a position in an exchange rather than a technology. Two requests to the same endpoint, one from a person's script and one from a hosted agent, are the same request to that endpoint unless something the request itself carries tells them apart.
→ probe402 identifies itself in every request it makes, and the user agent it sends is published in the method.
Sources
- The x402 specification repositoryx402 Foundation
- The AP2 specificationAgent Payments Protocol
- What is the Model Context Protocol?Model Context Protocol
- Agentic commerceStripe documentation
Related machine payment · buyer · agent wallet · facilitator · x402