.NET SDK for A2A Protocol (original) (raw)

A .NET library that helps run agentic applications as A2AServers following the Agent2Agent (A2A) Protocol.

The A2A .NET SDK provides a robust implementation of the Agent2Agent (A2A) protocol, enabling seamless communication between AI agents and applications. This library offers both high-level abstractions and fine-grained control, making it easy to build A2A-compatible agents while maintaining flexibility for advanced use cases.

Key features include:

Agent Capability Discovery: Retrieve agent capabilities and metadata through agent cards
Message-based Communication: Direct, stateless messaging with immediate responses
Task-based Communication: Create and manage persistent, long-running agent tasks
Streaming Support: Real-time communication using Server-Sent Events
ASP.NET Core Integration: Built-in extensions for hosting A2A agents in web applications
Cross-platform Compatibility: Supports .NET 8+

Protocol Compatibility

This library implements the A2A v1.0 specification. It provides full support for the JSON-RPC binding and HTTP+JSON REST binding, including streaming via Server-Sent Events.

If you're upgrading from the v0.3 SDK, see the Migration Guide for a comprehensive list of breaking changes and before/after code examples. A backward-compatible A2A.V0_3 NuGet package is available during the transition:

dotnet add package A2A.V0_3

Installation

Core A2A Library

ASP.NET Core Extensions

dotnet add package A2A.AspNetCore

Overview

Library: A2A

This library contains the core A2A protocol implementation. It includes the following key classes:

Client Classes

A2AClient: Primary client for making A2A requests to agents. Supports both streaming and non-streaming communication, task management, and push notifications.
A2ACardResolver: Resolves agent card information from A2A-compatible endpoints to discover agent capabilities and metadata.

Server Classes

TaskManager: Manages the complete lifecycle of agent tasks including creation, updates, cancellation, and event streaming. Handles both message-based and task-based communication patterns.
ITaskStore: An interface for abstracting the storage of tasks.
InMemoryTaskStore: Simple in-memory implementation of ITaskStore suitable for development and testing scenarios.

Core Models

AgentTask: Represents a task with its status, history, artifacts, and metadata.
AgentCard: Contains agent metadata, capabilities, and endpoint information.
Message: Represents messages exchanged between agents and clients.

Library: A2A.AspNetCore

This library provides ASP.NET Core integration for hosting A2A agents. It includes the following key classes:

Extension Methods

A2ARouteBuilderExtensions: Provides MapA2A() and MapHttpA2A() extension methods for configuring A2A endpoints in ASP.NET Core applications.

Getting Started

1. Create an Agent Server

using A2A; using A2A.AspNetCore;

var builder = WebApplication.CreateBuilder(args); var app = builder.Build();

var store = new InMemoryTaskStore(); var taskManager = new TaskManager(store);

taskManager.OnSendMessage = async (request, ct) => { var text = request.Message.Parts.FirstOrDefault()?.Text ?? ""; return new SendMessageResponse { Message = new Message { MessageId = Guid.NewGuid().ToString("N"), Role = Role.Agent, Parts = [Part.FromText($"Echo: {text}")] } }; };

var agentCard = new AgentCard { Name = "Echo Agent", Description = "Echoes messages back to the user", Version = "1.0.0", SupportedInterfaces = [new AgentInterface { Url = "http://localhost:5000/echo", ProtocolBinding = "JSONRPC", ProtocolVersion = "1.0" }], DefaultInputModes = ["text/plain"], DefaultOutputModes = ["text/plain"], Capabilities = new AgentCapabilities { Streaming = false }, Skills = [new AgentSkill { Id = "echo", Name = "Echo", Description = "Echoes back user messages", Tags = ["echo"] }], };

app.MapA2A(taskManager, "/echo"); app.MapWellKnownAgentCard(agentCard); app.Run();

2. Connect with A2AClient

using A2A;

// Discover agent var cardResolver = new A2ACardResolver(new Uri("http://localhost:5000/")); var agentCard = await cardResolver.GetAgentCardAsync();

// Create client using agent's endpoint var client = new A2AClient(new Uri(agentCard.SupportedInterfaces[0].Url));

// Send message var response = await client.SendMessageAsync(new SendMessageRequest { Message = new Message { MessageId = Guid.NewGuid().ToString("N"), Role = Role.User, Parts = [Part.FromText("Hello!")] } });

// Handle response switch (response.PayloadCase) { case SendMessageResponseCase.Message: Console.WriteLine(response.Message!.Parts[0].Text); break; case SendMessageResponseCase.Task: Console.WriteLine($"Task created: {response.Task!.Id}"); break; }

Samples

The repository includes several sample projects demonstrating different aspects of the A2A protocol implementation. Each sample includes its own README with detailed setup and usage instructions.

Agent Client Samples

samples/AgentClient/

Comprehensive collection of client-side samples showing how to interact with A2A agents:

Agent Capability Discovery: Retrieve agent capabilities and metadata using agent cards
Message-based Communication: Direct, stateless messaging with immediate responses
Task-based Communication: Create and manage persistent agent tasks
Streaming Communication: Real-time communication using Server-Sent Events

Agent Server Samples

samples/AgentServer/

Server-side examples demonstrating how to build A2A-compatible agents:

Echo Agent: Simple agent that echoes messages back to clients
Echo Agent with Tasks: Task-based version of the echo agent
Researcher Agent: More complex agent with research capabilities
HTTP Test Suite: Complete set of HTTP tests for all agent endpoints

Semantic Kernel Integration

samples/SemanticKernelAgent/

Advanced sample showing integration with Microsoft Semantic Kernel:

Travel Planner Agent: AI-powered travel planning agent
Semantic Kernel Integration: Demonstrates how to wrap Semantic Kernel functionality in A2A protocol

Command Line Interface

samples/A2ACli/

Command-line tool for interacting with A2A agents:

Direct command-line access to A2A agents
Useful for testing and automation scenarios

Quick Start with Client Samples

Clone and build the repository:
git clone https://github.com/a2aproject/a2a-dotnet.git
cd a2a-dotnet
dotnet build
Run the client samples:
cd samples/AgentClient
dotnet run

For detailed instructions and advanced scenarios, see the individual README files linked above.

Acknowledgements

This library builds upon Darrel Miller's sharpa2a project. Thanks to Darrel and all the other contributors for the foundational work that helped shape this SDK.

License

This project is licensed under the Apache 2.0 License.