Agent-to-Agent (A2A) Connection Guide

This guide provides a step-by-step walkthrough for connecting your Agentspace agent as an agent using the SSE (Server-Sent Events) protocol.

Overview

The Agent-to-Agent protocol enables standardized communication between AI agents through:

Agent Discovery: Retrieve agent metadata and capabilities
SSE Streaming: Real-time bidirectional communication
Context Management: Maintain conversation history across messages

Prerequisites

Before you begin, ensure you have:

Your agent deployed and accessible on Agentspace
A tool to make HTTP requests (curl, Postman, or a programming language HTTP client)
Ability to handle Server-Sent Events (SSE) streams

A2A Inspector Tool

For testing and validating your A2A connections, we recommend using the A2A Inspector - an open-source tool that helps you:

Validate agent cards and their structure
Test SSE streaming connections
Debug agent conversations in real-time
Visualize message flow and responses

GitHub Repository: https://github.com/a2aproject/a2a-inspector

Step 1: Get the Agent Card URL

The agent card is a JSON document that describes your agent’s capabilities, supported protocols, and available endpoints. It follows the standardized .well-known/agent.json convention.

Agent Card URL Structure

https://{host-domain}/discovery/{agent-id}/.well-known/agent.json

How to Obtain

Navigate to your Agentspace My Agents
Click the link below your deployed agent to open agent details page in new tab
Copy the agent card URL from the API Documentation tab

Agent Card URL Location — Click the link below your agent to open the agent details page in a new tab

Step 2: Discover Agent Card and Add Agent

Make a GET Request

Using curl

curl -X GET "{your-agent-card-url}" \
  -H "Accept: application/json"

Using JavaScript/Node.js

const agentCardUrl = "{your-agent-card-url}";

fetch(agentCardUrl)
  .then(response => response.json())
  .then(agentCard => console.log(agentCard))
  .catch(error => console.error('Error:', error));

Understanding the Agent Card Response

{
  "name": "Teacher Agent",
  "description": "An agent that explains concepts, summarizes text, and quizzes users on various topics.",
  "version": "1.0.0",
  "url": "https://{host-domain}/agent/{agent-id}",
  "protocolVersion": "0.3.0",
  "capabilities": {
    "streaming": true,
    "pushNotifications": false
  },
  "defaultInputModes": ["text"],
  "defaultOutputModes": ["text"],
  "skills": [
    {
      "description": "Use this tool when you want to understand any topic, from simple to complex.",
      "examples": ["Explain quantum computing like I'm 12."],
      "name": "Explain_Concept"
    }
  ]
}

Key fields:

name: The agent’s display name
url: The endpoint for sending messages (use this in Step 3)
description: Used by host agent to choose when to call this agent
version: Agent version

Agent Card Discovery — Sample Agent Card JSON response, viewed with the A2A inspector

Step 3: Send Messages via SSE Streaming

Use the url from your agent card response:

POST {agent-url-from-card}

Required Headers

Accept: text/event-stream
Content-Type: application/json
Cache-Control: no-store

Request Body Structure

{
  "id": "{unique-request-id}",
  "jsonrpc": "2.0",
  "method": "message/stream",
  "params": {
    "configuration": {
      "acceptedOutputModes": [],
      "blocking": true
    },
    "message": {
      "contextId": "{conversation-context-id}",
      "kind": "message",
      "messageId": "{unique-message-id}",
      "parts": [
        {
          "kind": "text",
          "text": "Your message here"
        }
      ],
      "role": "user"
    }
  }
}

Field Descriptions

Field	Description	Required	Notes
`id`	Unique request identifier	Yes	Generate a new UUID for each request
`jsonrpc`	JSON-RPC version	Yes	Always `"2.0"`
`method`	RPC method name	Yes	Use `"message/stream"` for SSE
`params.configuration.blocking`	Wait for complete response	Yes	`true` for synchronous, `false` for async
`params.message.contextId`	Conversation context ID	Yes	Keep the same ID to maintain conversation history
`params.message.messageId`	Unique message identifier	Yes	Generate a new UUID for each message
`params.message.parts`	Message content array	Yes	Can contain text, images, or other content types
`params.message.role`	Message sender role	Yes	Typically `"user"` or `"assistant"`

SSE Streaming — A streamed conversation with status updates, viewed with the A2A Inspector

Complete JavaScript/Node.js Example

const fetch = require('node-fetch');
const { v4: uuidv4 } = require('uuid');

const agentEndpoint = "{agent-url-from-card}";

const requestId = uuidv4();
const contextId = uuidv4();  // Keep this for conversation continuity
const messageId = uuidv4();

const payload = {
  id: requestId,
  jsonrpc: "2.0",
  method: "message/stream",
  params: {
    configuration: {
      acceptedOutputModes: [],
      blocking: true
    },
    message: {
      contextId: contextId,
      kind: "message",
      messageId: messageId,
      parts: [{ kind: "text", text: "What is the capital of France?" }],
      role: "user"
    }
  }
};

fetch(agentEndpoint, {
  method: 'POST',
  headers: {
    'Accept': 'text/event-stream',
    'Content-Type': 'application/json',
    'Cache-Control': 'no-store'
  },
  body: JSON.stringify(payload)
})
.then(response => {
  const reader = response.body;
  reader.on('data', (chunk) => {
    const lines = chunk.toString().split('\n');
    lines.forEach(line => {
      if (line.startsWith('data: ')) {
        try {
          const parsed = JSON.parse(line.substring(6));
          if (parsed.kind === 'status-update') {
            console.log('Status:', parsed.status.state);
          } else if (parsed.kind === 'artifact-update') {
            console.log('Response:', parsed.artifact.parts[0].text);
          }
        } catch (e) {}
      }
    });
  });
  reader.on('end', () => console.log('Stream ended'));
})
.catch(error => console.error('Error:', error));

Understanding SSE Responses

Common Response Types

Status Update

{
  "kind": "status-update",
  "contextId": "{context-id}",
  "taskId": "{task-id}",
  "final": false,
  "status": {
    "state": "working",
    "timestamp": "{timestamp}",
    "message": {
      "kind": "message",
      "messageId": "{msg-id}",
      "role": "agent",
      "parts": [{ "kind": "text", "text": "Processing your request..." }]
    }
  }
}

Artifact Update

{
  "kind": "artifact-update",
  "contextId": "{context-id}",
  "taskId": "{task-id}",
  "artifact": {
    "artifactId": "{artifact-id}",
    "name": "agent_response",
    "parts": [{ "kind": "text", "text": "The capital of France is Paris..." }]
  }
}

Response Type Summary

Response Type	`kind` Value	Purpose
Status Update	`status-update`	Progress and reasoning
Artifact Update	`artifact-update`	The actual answer or output

Multi-Turn Conversations

To maintain conversation context, use the same contextId across multiple messages:

const contextId = uuidv4();

// First message
sendMessage(contextId, "What is the capital of France?");

// Follow-up message (same contextId)
sendMessage(contextId, "What about its population?");

Create a new contextId to start a fresh conversation.

Best Practices

Always generate unique UUIDs for id (per request) and messageId (per message).
Re-use contextId within a conversation to preserve history.
Handle both status-update and artifact-update events in your stream processor.
Implement connection pooling and rate limiting when scaling your integration.

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Agent-to-Agent (A2A) Connection

Agent-to-Agent (A2A) Connection Guide

Overview

Prerequisites

A2A Inspector Tool

Step 1: Get the Agent Card URL

Agent Card URL Structure

How to Obtain

Step 2: Discover Agent Card and Add Agent

Make a GET Request

Using curl

Using JavaScript/Node.js

Understanding the Agent Card Response

Step 3: Send Messages via SSE Streaming

Required Headers

Request Body Structure

Field Descriptions

Complete JavaScript/Node.js Example

Understanding SSE Responses

Common Response Types

Status Update

Artifact Update

Response Type Summary

Multi-Turn Conversations

Best Practices

​Agent-to-Agent (A2A) Connection Guide

​Overview

​Prerequisites

​A2A Inspector Tool

​Step 1: Get the Agent Card URL

​Agent Card URL Structure

​How to Obtain

​Step 2: Discover Agent Card and Add Agent

​Make a GET Request

​Using curl

​Using JavaScript/Node.js

​Understanding the Agent Card Response

​Step 3: Send Messages via SSE Streaming

​Required Headers

​Request Body Structure

​Field Descriptions

​Complete JavaScript/Node.js Example

​Understanding SSE Responses

​Common Response Types

​Status Update

​Artifact Update

​Response Type Summary

​Multi-Turn Conversations

​Best Practices

Agent-to-Agent (A2A) Connection Guide

Overview

Prerequisites

A2A Inspector Tool

Step 1: Get the Agent Card URL

Agent Card URL Structure

How to Obtain

Step 2: Discover Agent Card and Add Agent

Make a GET Request

Using curl

Using JavaScript/Node.js

Understanding the Agent Card Response

Step 3: Send Messages via SSE Streaming

Required Headers

Request Body Structure

Field Descriptions

Complete JavaScript/Node.js Example

Understanding SSE Responses

Common Response Types

Status Update

Artifact Update

Response Type Summary

Multi-Turn Conversations

Best Practices