a2aproject/a2a-dotnet

A2A .NET SDK is a C# library that implements the Agent2Agent (A2A) Protocol for building agentic applications as A2A-compatible servers.

The library addresses the need for standardized communication between AI agents and applications. It provides both high-level abstractions and fine-grained control over agent interactions, supporting three protocol bindings: JSON-RPC, HTTP+JSON REST with Server-Sent Events streaming, and gRPC with server-streaming. The core abstractions—IA2AClient for client operations and IA2ARequestHandler for server-side request handling—are shared across all bindings, allowing developers to write binding-agnostic code. Key capabilities include agent capability discovery through agent cards, direct stateless message-based communication, persistent long-running task management, and real-time streaming support.

Developers should adopt this tool if they are building .NET applications that need to communicate with A2A-compatible agents or expose agent functionality through standard A2A endpoints. It suits projects targeting .NET 8 and later that require interoperability with the broader A2A ecosystem. The library includes built-in ASP.NET Core integration for hosting agents in web applications, making it particularly valuable for teams already invested in the .NET platform. The README indicates that a backward-compatible v0.3 package is available for gradual migration, though upgrading to v1.0 involves breaking changes documented in a migration guide. The compatibility layer includes specific guidance on blocking behavior differences when v0.3 clients communicate with v1 servers.

The project maintains active development with regular updates to align with the A2A v1.0 specification. The codebase includes comprehensive documentation covering protocol bindings, migration paths, and integration patterns. The library is distributed across modular NuGet packages, allowing consumers to depend only on required components—the core library, ASP.NET Core extensions, or gRPC bindings—rather than forcing unnecessary dependencies.