A2A LangGraph ReAct Agent

A TypeScript project that implements an A2A-compatible agent using LangGraph's ReAct agent with Model Context Protocol (MCP) integration.

Project Structure

a2a-langgraph-agent/
├── src/                      # TypeScript source files
│   ├── index.ts              # Server entry point
│   ├── cli.ts                # CLI client for interacting with the agent
│   └── a2a/                  # A2A implementation
│       ├── executor.ts       # LangGraph React agent executor
│       ├── agentCard.ts      # Agent card definition
│       ├── tools.ts          # Local tool definitions
│       └── mcp/              # Model Context Protocol integration
│           ├── client.ts     # MCP client implementation
│           └── mcp-servers.json # MCP server configurations
├── dist/                     # Compiled JavaScript output (generated)
├── tsconfig.json             # TypeScript configuration
├── package.json              # Project configuration and dependencies
└── README.md                 # This file

Prerequisites

• Node.js (v16 or higher recommended)
• npm (comes with Node.js)

Installation

Clone the repository and install dependencies:

git clone <repository-url>
cd a2a-langgraph-agent
npm install

OpenAI API Key Configuration

The agent uses OpenAI's models through LangChain. You'll need to set up your OpenAI API key as an environment variable:

# For Linux/macOS
export OPENAI_API_KEY=your-api-key-here

# For Windows (Command Prompt)
set OPENAI_API_KEY=your-api-key-here

# For Windows (PowerShell)
$env:OPENAI_API_KEY="your-api-key-here"

Alternatively, you can create a .env file in the project root:

OPENAI_API_KEY=your-api-key-here

Running the Agent

Start the Agent Server

In one terminal, start the agent server:

npm run dev

This will start the A2A server on http://localhost:3000.

Use the CLI Client

In another terminal, use the CLI client to interact with the agent:

npm run cli

You can also specify a different server URL:

npm run cli http://localhost:3000

CLI Commands

• Type your message and press Enter to send it to the agent
• /new - Start a new session (clears task and context IDs)
• /exit - Exit the CLI

Available Scripts

In the project directory, you can run:

npm run build

Compiles the TypeScript code to JavaScript in the dist directory.

npm run start

Runs the compiled JavaScript from the dist directory.

npm run dev

Runs the agent server directly using tsx without compiling.

npm run cli

Runs the CLI client to interact with the agent.

Features

• A2A Protocol Support: Implements the A2A protocol for agent communication
• LangGraph React Agent: Uses LangChain's React agent for reasoning and tool use
• Built-in Tools: Includes calculator and time tools out of the box
• MCP Integration: Connects to external Model Context Protocol servers
• CLI Client: Interactive command-line interface for testing the agent

Built-in Tools

The agent comes with several built-in tools defined in src/a2a/tools.ts:

Calculator Tool

Performs basic mathematical operations:

• Addition
• Subtraction
• Multiplication
• Division

Example usage: "Calculate 25 divided by 5" or "What's 123 + 456?"

Current Time Tool

Returns the current date and time.

Example usage: "What time is it?" or "Tell me the current date"

MCP Integration

Configuring MCP Servers

The agent can connect to external Model Context Protocol (MCP) servers to extend its capabilities. MCP servers are configured in the src/a2a/mcp/mcp-servers.json file.

Example configuration:

{
  "github": {
    "command": "npx",
    "args": [
      "-y",
      "@modelcontextprotocol/server-github"
    ],
    "env": {
      "GITHUB_PERSONAL_ACCESS_TOKEN": "your-github-token"
    }
  }
}

Each entry in the JSON file represents an MCP server with:

• A unique name (e.g., "github")
• The command to run the server
• Command arguments
• Environment variables needed by the server

The agent will automatically start these MCP servers when it initializes and make their tools available to the LangGraph React agent.

Available MCP Servers

The project is configured to work with various MCP servers, including:

• GitHub: Interact with GitHub repositories, issues, and pull requests
• Weather: Get weather forecasts and conditions
• Search: Perform web searches
• File System: Access and manipulate files

To use these servers, you'll need to configure them in the mcp-servers.json file with appropriate credentials.

Dependencies

• @a2a-js/sdk: A2A JavaScript SDK
• @langchain/langgraph: LangChain's LangGraph library for agent workflows
• @langchain/openai: LangChain's OpenAI integration
• @langchain/mcp-adapters: Model Context Protocol adapters for LangChain
• express: Web server framework
• uuid: For generating unique IDs
• zod: Schema validation for tool definitions

License

MIT