Agent Card
Quick Take
- In brief: An Agent Card is a machine-readable description of an A2A service.
- Useful for: Helping a client discover an agent’s endpoint and advertised capabilities.
- Main limit: A card describes a service; it does not prove that the service works.
Overview
Before calling a remote agent, a client needs to know where to send a request and what the service claims to support. An Agent Card provides that information in a form software can read.
Core Definition
An A2A Agent Card describes a service’s identity, interfaces, capabilities, skills, and authentication requirements.
Background and Evolution
Service registries have long used machine-readable descriptions to support discovery. A2A uses an Agent Card to make agent capabilities discoverable across independently built systems.
How It Works
A service publishes or shares a card. A client reads its endpoint, input and output modes, skills, and authentication details, then decides whether to call it. The service can expose a public card or a restricted extended card.
Applications in Software Development and Testing
A test client can read a card, verify required fields, and test the listed operations against the service. These checks help catch stale endpoints or missing authentication before a workflow depends on them.
Strengths and Limitations
A structured card is easier to inspect and validate than informal documentation. It can become stale, and its advertised capabilities still require runtime testing.
Comparison with Similar Terms
An Agent Card describes one agent service. A2A defines the interactions between services. A service registry may store or distribute cards but is not the protocol itself.
Best Practices
Version the card with the service, validate its schema in CI, protect private cards, and avoid placing secrets in the document.
Common Pitfalls
Do not assume that a valid card proves the endpoint is available, authorized for the caller, or capable of producing correct results.
FAQ
Does an Agent Card have to be public?
No. A service can share it through public discovery, an enterprise registry, or private configuration.