A2A AgenticDirect

Clean, schema-driven implementation of A2A (Agent-to-Agent) protocol with MCP (Model Context Protocol) integration for OpenDirect v2.1.

Architecture

┌─────────────────────────────────────────────────────────────────┐
│ opendirect.json │
│ (OpenAPI 3.0 Schema) │
└──────────────────────┬──────────────────────────────────────────┘
│
│ Parsed by SchemaParser
▼
┌─────────────────────────────────────────────────────────────────┐
│ MCP Server Layer │
│ • Auto-generates tools from schema │
│ • Handles tool execution │
│ • Returns mock responses │
└──────────────────────┬──────────────────────────────────────────┘
│
│ Provides tool handlers
▼
┌─────────────────────────────────────────────────────────────────┐
│ A2A Agent Layer │
│ • Agent Card Generator (v0.3.0) │
│ • JSON-RPC 2.0 Router │
│ • Agent Executor (OpenAI-powered) │
│ • Task Management │
└──────────────────────┬──────────────────────────────────────────┘
│
│ HTTP/JSON-RPC
▼
┌─────────────────────────────────────────────────────────────────┐
│ JavaScript Client │
│ • @a2a-js/sdk integration │
│ • Agent discovery │
│ • Message sending │
│ • Task polling │
└─────────────────────────────────────────────────────────────────┘

Features

Server (TypeScript)

• Schema-Driven: Automatically generates MCP tools from OpenAPI spec
• A2A v0.3.0 Compliant: Full agent card with skills, OAuth2, interfaces
• AI-Powered Execution: Uses OpenAI GPT-4o-mini for tool selection
• Dual Agents: Separate buyer and seller agents with role-specific skills
• JSON-RPC 2.0: Standard protocol for agent communication
• Dynamic URLs: Auto-detects URLs from request headers (Cloud Run ready)
• Task Management: Full task lifecycle (pending → working → completed/failed)

Client (JavaScript)

• @a2a-js/sdk: Official A2A SDK integration
• Agent Discovery: Automatic agent card fetching
• Real-time Updates: Task polling for response updates
• Quick Actions: Pre-built message templates
• Clean UI: Modern, responsive interface

Project Structure

a2a-agenticdirect/
├── server/ # TypeScript server
│ ├── src/
│ │ ├── types/
│ │ │ └── index.ts # Type definitions
│ │ ├── mcp/
│ │ │ ├── schema-parser.ts # OpenAPI → MCP tools
│ │ │ └── mcp-server.ts # MCP protocol handler
│ │ ├── a2a/
│ │ │ ├── agent-card.ts # Agent card generator
│ │ │ ├── executor.ts # AI-powered execution
│ │ │ └── router.ts # Express routes
│ │ └── server.ts # Main entry point
│ ├── package.json
│ └── tsconfig.json
├── client/ # JavaScript client
│ ├── src/
│ │ └── app.js # A2A SDK ClientFactory implementation
│ ├── dist/
│ │ └── bundle.js # Bundled client (generated)
│ ├── index.html
│ ├── style.css
│ └── package.json
├── opendirect.json # OpenAPI schema
└── README.md

Setup

Prerequisites

• Node.js 20+
• OpenAI API key

Server Setup

1. Navigate to server directory:

cd server

2. Install dependencies:

npm install

3. Create .env file:

cp .env.example .env

4. Add your OpenAI API key to .env:

OPENAI_API_KEY=sk-...OPENAI_MODEL=gpt-4o-miniPORT=3000

5. Build and start:

# Development (with auto-reload)
npm run dev
# Production
npm run build
npm start

Server will start on http://localhost:3000

Client Setup

1. Navigate to client directory:

cd client

2. Install dependencies:

npm install

3. Build and run:

# Development mode (with hot reload and bundling)
npm run dev
# Or build once and serve
npm run build
npm run serve

Client will be available at http://localhost:8080

Note: The client uses esbuild to bundle @a2a-js/sdk into dist/bundle.js. Always run npm run dev or npm run build before accessing the client.

Usage

Using the Web Client

1. Open http://localhost:8080 in your browser
2. Configure:
   • Server URL: http://localhost:3000
   • Agent Role: buyer or seller
3. Click Connect to Agent
4. Send messages using quick actions or custom text

Example messages for Buyer Agent:

• "Create an account for Nike"
• "Create an order for Adidas campaign"
• "Submit creative for Nike banner ad"
• "List available products"

Example messages for Seller Agent:

• "List available products"
• "Process order for account ABC"
• "Approve creative submission"

Using curl (JSON-RPC)

Get Agent Card

curl http://localhost:3000/a2a/buyer/.well-known/agent-card.json

Send Message

curl -X POST http://localhost:3000/a2a/buyer/jsonrpc \
-H "Content-Type: application/json" \
-d '{ "jsonrpc": "2.0", "method": "sendMessage", "params": { "message": { "role": "user", "parts": [{"kind": "text", "text": "Create an account for Nike"}], "kind": "message" } }, "id": 1 }'

Response:

{
"jsonrpc": "2.0",
"result": {
"id": "task-uuid",
"status": {
"state": "working",
"timestamp": "2025-01-02T..."
}
},
"id": 1
}

Get Task Status

curl -X POST http://localhost:3000/a2a/buyer/jsonrpc \
-H "Content-Type: application/json" \
-d '{ "jsonrpc": "2.0", "method": "getTask", "params": { "taskId": "task-uuid" }, "id": 2 }'

API Reference

Endpoints

GET /

Server information and available agents

GET /health

Health check endpoint

GET /a2a/{role}/.well-known/agent-card.json

Agent card discovery (A2A v0.3.0)

POST /a2a/{role}/jsonrpc

JSON-RPC 2.0 endpoint for agent communication

Methods:

• sendMessage - Send message to agent
• getTask - Get task status
• cancelTask - Cancel task

Agent Card Schema

{
"name": "opendirect-buyer-agent",
"protocolVersion": "0.3.0",
"version": "1.0.0",
"url": "http://localhost:3000/a2a/buyer",
"description": "...",
"skills": [
{
"id": "order-creation",
"name": "Order Creation",
"description": "Create and manage advertising orders",
"tags": ["advertising", "order"],
"examples": [
"Create an account for Nike",
"Create an order for Adidas campaign"
],
"inputModes": ["application/json"],
"outputModes": ["application/json"]
}
],
"capabilities": {
"pushNotifications": false,
"streaming": true,
"mcpIntegration": true
},
"securitySchemes": {
"oauth2": {
"type": "oauth2",
"flows": {
"clientCredentials": {...},
"authorizationCode": {...}
}
}
},
"additionalInterfaces": [
{
"protocol": "jsonrpc",
"version": "2.0",
"transport": "http",
"url": "http://localhost:3000/a2a/buyer/jsonrpc"
},
{
"protocol": "mcp",
"version": "2024-11-05",
"transport": "sse",
"tools": ["create_account", "create_order", ...]
}
]
}

How It Works

1. Schema Parsing

SchemaParser reads opendirect.json (OpenAPI 3.0 spec) and extracts:

• Operations → MCP tool names (e.g., create_account)
• Parameters → Input schemas
• Request bodies → Additional parameters

2. MCP Tool Generation

MCPServer creates tool handlers for each operation:

• Validates input against schema
• Executes tool (currently returns mock data)
• Returns structured response

3. A2A Agent Layer

AgentCardGenerator creates compliant agent cards with:

• Dynamic URL detection (X-Forwarded-* headers)
• Role-specific skills with examples
• OAuth2 security schemes
• MCP integration metadata

4. AI-Powered Execution

AgentExecutor uses OpenAI to:

• Analyze user message
• Select appropriate tool
• Extract parameters
• Execute and respond

5. Task Management

A2ARouter handles:

• Message reception
• Task creation and tracking
• Asynchronous execution
• Status polling

Environment Variables

Variable	Required	Default	Description
OPENAI_API_KEY	Yes	-	OpenAI API key
OPENAI_MODEL	No	gpt-4o-mini	OpenAI model
PORT	No	3000	Server port
NODE_ENV	No	development	Environment
PROTOCOL	No	Auto-detect	Override protocol (http/https)
HOST	No	Auto-detect	Override host

Development

Build Server

cd server
npm run build

Watch Mode

cd server
npm run dev

Add New Tools

Tools are automatically generated from opendirect.json. To add new tools:

1. Update opendirect.json with new operations
2. Restart server - tools auto-refresh

Customize Tool Handlers

Edit server/src/mcp/mcp-server.ts:

privatecreateToolHandler(tool: MCPTool): MCPToolHandler{returnasync(params: any)=>{// Add custom logic hereif(tool.name==='create_account'){// Call actual APIreturnawaityourAPI.createAccount(params);}// Default mock responsereturnthis.generateMockResponse(tool.name,params);};}

Testing

Test Agent Card

curl http://localhost:3000/a2a/buyer/.well-known/agent-card.json | jq

Test Message Flow

# 1. Send message
TASK_ID=$(curl -X POST http://localhost:3000/a2a/buyer/jsonrpc \ -H "Content-Type: application/json" \ -d '{ "jsonrpc": "2.0", "method": "sendMessage", "params": { "message": { "role": "user", "parts": [{"kind": "text", "text": "Create an account for Nike"}], "kind": "message" } }, "id": 1 }'| jq -r '.result.id')# 2. Check task status
curl -X POST http://localhost:3000/a2a/buyer/jsonrpc \
-H "Content-Type: application/json" \
-d "{\"jsonrpc\": \"2.0\",\"method\": \"getTask\",\"params\": {\"taskId\": \"$TASK_ID\" },\"id\": 2 }"| jq

Troubleshooting

"No response from AI"

• Check OpenAI API key is valid
• Verify API quota not exceeded
• Check network connectivity

"Tool not found"

• Restart server to refresh tools from schema
• Verify opendirect.json contains operation

Task stuck in "working"

• Check server logs for errors
• Verify OpenAI API is responding
• Check for rate limiting

Agent card shows localhost in production

• Ensure reverse proxy sets X-Forwarded-Proto and X-Forwarded-Host
• Or set PROTOCOL and HOST environment variables

Credits

• Built with A2A Protocol v0.3.0
• Uses @a2a-js/sdk
• Implements MCP (Model Context Protocol)
• Based on OpenDirect v2.1