How Agents Find Each Other

In A2A, every agent publishes an Agent Card - a JSON metadata document hosted at a standard endpoint: /.well-known/agent-card.json.

Agent Card Structure

{
  "name": "TravelBooker",
  "description": "Books flights, hotels, and rental cars",
  "version": "2.1.0",
  "url": "https://travel-agent.example.com/a2a",
  "capabilities": {
    "tasks": ["book_flight", "search_hotels", "rent_car"],
    "streaming": true,
    "pushNotifications": true
  },
  "authentication": {
    "type": "oauth2",
    "authorizationUrl": "https://travel-agent.example.com/auth"
  },
  "skills": [
    {
      "id": "book_flight",
      "name": "Flight Booking",
      "description": "Search and book flights. Supports one-way and round-trip.",
      "inputSchema": { "type": "object", "properties": { "origin": {}, "destination": {}, "date": {} } }
    }
  ]
}

Discovery Flow

1. Client agent queries /.well-known/agent-card.json at the target URL.
2. Reads capabilities: What tasks can this agent handle? What auth does it need?
3. Authenticates if required (OAuth 2.0, API keys, or open access).
4. Creates a Task - sends a structured request to the remote agent.