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A2A reference

The agent surface is A2A (Agent-to-Agent) JSON-RPC 2.0. This section is for integrations. If you are using the Reach Agent inside Gemini Enterprise, you do not need anything here. Start at Using the agent.

Base URL

https://agents.reach.dog

Use this host. Read it from configuration rather than compiling it into a client, and never call the underlying Cloud Run hostname directly: that value changes when the service is re-homed, and a previously published one has already gone dead once.

Discovery

Endpoint Returns
GET /.well-known/agent-card.json The Reach Agent card. The primary discovery document
GET /ge/.well-known/agent-card.json The same card with the Gemini Enterprise endpoint as its url
GET /.well-known/agents.json Every card, Reach Agent first, specialists after
GET /health Liveness. Returns 200 while the service is up

The card is the contract. Read the endpoint, the protocol version, the declared capabilities, and the skill list from it rather than from this page.

Protocol

A2A JSON-RPC 2.0, protocol version 0.3.0. Methods message/send and message/stream. Full request and response shapes are in JSON-RPC format.

Streaming is declared and supported. Push notifications and task state history are not.

Rendering

The card declares the A2UI v0.8 extension. A client that sends the matching capability receives structured interface parts alongside the text, which is how tables, cards, and tappable controls are drawn. A client that does not gets the text answer and can ignore the rest.

Sections

  • Access. What is required to call the surface, and what the response headers tell you.
  • Endpoints. The full endpoint table.
  • JSON-RPC format. Request, response, task lifecycle, errors.