A2A Agent Card – Definition
An Agent Card is the public profile of an A2A agent, served at /.well-known/agent-card.json. It tells other agents what this agent is called, where to reach it, which protocol version it speaks and which skills it offers. A2A (Agent2Agent) is the open protocol for agents talking to other agents.
The business card one AI agent reads before it hands a task to another.
What A2A is
A2A (Agent2Agent) is an open protocol for agents to talk to other agents. Google contributed it to the Linux Foundation; version 1.0 is out, and the latest release is v1.0.1. Where MCP connects an agent to tools, A2A connects an agent to another agent that can take on a task.
What an Agent Card contains
The Agent Card is the agent’s public profile, served at /.well-known/agent-card.json. The required fields in A2A 1.0 are:
| Field | What it says |
|---|---|
name, description, version | Who the agent is |
supportedInterfaces | Where to reach it and with which protocol version |
capabilities | For example streaming or push notifications |
defaultInputModes, defaultOutputModes | Media types it accepts and returns |
skills | The tasks it can do |
Optional fields include provider, securitySchemes, documentationUrl, iconUrl and signatures.
{
"name": "Example Store shopping agent",
"description": "Finds products, checks stock and prepares carts for Example Store.",
"version": "1.2.0",
"supportedInterfaces": [
{ "url": "https://shop.example/a2a/v1", "protocolBinding": "JSONRPC", "protocolVersion": "1.0" }
],
"capabilities": { "streaming": false, "pushNotifications": false },
"defaultInputModes": ["text/plain"],
"defaultOutputModes": ["text/plain", "application/json"],
"skills": [
{ "id": "product-search", "name": "Product search",
"description": "Search the catalogue by text, price and availability.",
"tags": ["catalog", "search"] }
]
}The path changed
Before A2A 0.3 the card lived at /.well-known/agent.json. Many published cards are still there, where a 1.0 client never looks. If you have a card, check the path first.
Does a store need one?
Only if the store runs its own agent. Most shops do not. The case where it becomes required: a UCP profile may list a2a as a transport, pointing at the Agent Card. A profile that declares A2A without a readable card at the canonical path advertises a door with nothing behind it.
The angeo AEO audit checks exactly that as the agent_card signal: required when your UCP profile declares A2A, informational otherwise, and a warning if a card sits only at the old path.
Questions
- What is an A2A Agent Card?
- A JSON document at /.well-known/agent-card.json that describes an A2A agent: its name, where to reach it, which protocol version it speaks, what it accepts and returns, and which skills it offers.
- What is the A2A protocol?
- Agent2Agent, an open protocol for agents to communicate with other agents. It is a Linux Foundation project contributed by Google; version 1.0 is released.
- Where should the Agent Card be served?
- At /.well-known/agent-card.json. Before A2A 0.3 it was /.well-known/agent.json, which 1.0 clients no longer check.
- Does an online store need an Agent Card?
- Only if it runs its own agent, or its UCP profile declares an a2a transport. Most stores need neither.
- What is the difference between A2A and MCP?
- MCP connects an agent to tools and data. A2A connects an agent to another agent that can take on a task.
Related
- MCP for commerce – definition
- UCP – definition
- /.well-known/ucp – definition
- Commerce agent – definition
- AEO score – definition