A2UI LiveView

A2UI LiveView is a Phoenix LiveView renderer and session engine for the Agent-to-UI A2UI protocol. It consumes JSONL protocol messages and renders declarative UIs in real time, while forwarding user actions back to your agent or backend.

It supports protocol v0.8 (stable) and v0.9 (draft), including version-aware catalog negotiation, action envelopes, data model broadcasting and A2UI Extension for A2A Protocol.

Features

• Parse and apply A2UI JSONL messages with A2UI.Session.
• Render surfaces in LiveView via A2UI.Phoenix.Live.
• Standard Phoenix catalog with layout, display, and input components.
• Two-way data binding for inputs and version-aware user action envelopes.
• Optional event transport for forwarding actions/errors to external agents.

Quickstart

Add a LiveView that delegates A2UI events to A2UI.Phoenix.Live and stream JSONL lines into the session.

defmodule MyAppWeb.AgentUiLive do
  use MyAppWeb, :live_view

  def mount(_params, _session, socket) do
    {:ok, A2UI.Phoenix.Live.init(socket)}
  end

  def handle_info({:a2ui, json_line}, socket) do
    A2UI.Phoenix.Live.handle_a2ui_message({:a2ui, json_line}, socket)
  end

  def handle_event("a2ui:" <> _ = event, params, socket) do
    A2UI.Phoenix.Live.handle_a2ui_event(event, params, socket)
  end

  def render(assigns) do
    ~H"""
    <Layouts.app flash={@flash} current_scope={@current_scope}>
      <A2UI.Phoenix.LiveView.render surfaces={@a2ui_surfaces} />
    </Layouts.app>
    """
  end
end

To push protocol messages into the LiveView, send JSONL lines into the mailbox:

send(pid, {:a2ui, json_line})

Protocol Versions

The session detects the protocol version per surface and applies the correct envelopes:

• v0.8 uses {"userAction": ...} action envelopes.
• v0.9 uses {"action": ...} action envelopes and supports data model broadcasts.

Catalog negotiation is version-aware, so v0.8 and v0.9 clients can request the correct catalog identifiers.

Demo

The demo application lives in demo/ and shows both v0.8 and v0.9 flows with LiveView surfaces, plus an HTTP+SSE and A2A transport for external agents.

Links

• A2UI docs
• A2UI protocol specs: -- v0.8 (stable) -- v0.9 (draft) -- A2UI Extension for A2A Protocol
• A2A docs
• Demo app: [demo]