elizaOS A2A (Agent-to-Agent) Server Examples

This directory contains A2A (Agent-to-Agent) server implementations that expose an elizaOS agent as an HTTP server. This enables agent-to-agent communication, webhooks, and integration with other AI systems.

Uses real elizaOS runtime.

If OPENAI_API_KEY is set, the server will use an OpenAI-backed model (and SQL where supported).
If OPENAI_API_KEY is not set, the server runs in a deterministic “ELIZA classic” mode (no API keys required), backed by @elizaos/plugin-inmemorydb for ephemeral multi-turn state.

Available Examples

Framework	Language	Directory
Express.js	TypeScript	`.`

What is A2A?

A2A (Agent-to-Agent) is a pattern where AI agents communicate with each other over HTTP. Each agent exposes a simple API that allows:

Sending messages to the agent
Receiving responses
Querying agent capabilities
Multi-turn conversations with session management

Common API Endpoints

All implementations expose the same REST API:

`GET /`

Returns information about the agent.

bash

curl http://localhost:3000/

Response:

json

{
  "name": "Eliza",
  "bio": "A helpful AI assistant",
  "version": "2.0.0-beta.0",
  "capabilities": ["chat", "reasoning", "tool-use"],
  "powered_by": "elizaOS"
}

`GET /health`

Health check endpoint.

bash

curl http://localhost:3000/health

`POST /chat`

Send a message to the agent and receive a response.

bash

curl -X POST http://localhost:3000/chat \
  -H "Content-Type: application/json" \
  -d '{"message": "Hello, how are you?", "sessionId": "user-123"}'

Response:

json

{
  "response": "Hello! I'm doing well, thank you for asking. How can I help you today?",
  "agentId": "eliza-agent-id",
  "sessionId": "user-123",
  "timestamp": "2024-01-10T12:00:00Z"
}

`POST /chat/stream`

Stream a response from the agent (SSE).

bash

curl -X POST http://localhost:3000/chat/stream \
  -H "Content-Type: application/json" \
  -H "Accept: text/event-stream" \
  -d '{"message": "Tell me a story"}'

Quick Start

bash

cd examples/a2a
bun install
bun run start

Configuration

Optional: OpenAI API key (enables OpenAI-backed responses):

bash

export OPENAI_API_KEY=your-key

Optional configuration:

PORT - Server port (default: 3000)
OPENAI_BASE_URL - Custom OpenAI-compatible endpoint
OPENAI_SMALL_MODEL - Model for quick responses
OPENAI_LARGE_MODEL - Model for complex responses

Use Cases

Multi-Agent Systems: Have multiple agents communicate with each other
Webhooks: Receive events from external services and have the agent respond
Chatbots: Deploy agents as backend services for chat applications
API Integration: Integrate agents into existing API-based workflows
Testing: Test agent behavior programmatically

Testing

bash

cd examples/a2a
bun run test

Agent-to-Agent Communication Example

bash

# Agent A calls Agent B
curl -X POST http://agent-b:3000/chat \
  -H "Content-Type: application/json" \
  -H "X-Agent-Id: agent-a" \
  -d '{
    "message": "Can you help me analyze this data?",
    "context": {"source": "agent-a", "task": "data-analysis"}
  }'