An agent card is an A2A JSON document that introduces an agent to potential clients. It identifies the agent, describes its role, specifies the request endpoint, and advertises capabilities such as streaming. section 9.6.1
Servers publish the card at /.well-known/agent.json. Clients read it to decide which agent fits a request, then send standardized task requests to the declared URL. section 9.6.1 section 9.6.2
A practical card commonly contains:
- name: the agent identifier used by clients and routing logic. section 9.6.1
- description: a capability summary used by LLMs when selecting an agent. section 9.6.1
- url: the endpoint where clients submit task requests. section 9.6.1
- capabilities: supported features such as streaming, alongside metadata such as version. section 9.6.1
Math expert card
A card can identify a math_expert agent, describe mathematical calculations and equation solving, publish http://localhost:9999/, declare version 1.0.0, and enable streaming. section 9.6.1 section 9.6.2
Figure 9.12 A2A client-server model: client queries agent card and sends task requests, server provides agent information and executes tasks.
Use the client-server flow to trace card discovery, request submission, server execution, and response delivery. section 9.6.1
