TLDR: Microsoft has released the A2A .NET SDK, a new developer toolkit that enables .NET developers to build AI agents capable of communicating and collaborating seamlessly using the open Agent2Agent (A2A) protocol. This SDK aims to address the challenge of inter-agent communication in an increasingly complex AI ecosystem, fostering distributed intelligence and enhancing frameworks like Semantic Kernel.
The rapidly evolving landscape of Artificial Intelligence has led to a proliferation of autonomous AI agents, each specialized in handling diverse and complex tasks, ranging from customer service to data analysis and workflow orchestration. A critical challenge arising from this growth is the need for these independent agents, often built with different frameworks and by various vendors, to discover, communicate, and collaborate effectively. To address this, Microsoft has announced the release of the Agent2Agent (A2A) .NET SDK, an implementation of the open A2A protocol designed to standardize inter-agent communication.
Released on July 31st, 2025, the A2A .NET SDK empowers .NET developers to create both A2A servers and clients, facilitating seamless interaction between AI agents within the broader ecosystem, regardless of their underlying technology stack. This initiative significantly strengthens the existing AI ecosystem, particularly benefiting developers utilizing Azure AI Foundry and Semantic Kernel. Semantic Kernel, which already incorporates A2A agent capabilities through its Python and .NET implementations, can now leverage this community-driven .NET SDK to more rapidly adopt the latest A2A protocol features while maintaining its enterprise-grade stability.
The Agent2Agent (A2A) Protocol itself is an open standard focused on enabling AI agents to:
Discover each other’s capabilities: Agents can identify what other agents can do.
Negotiate interaction modalities: Supports various communication formats like text, forms, and media.
Securely collaborate on long-running tasks: Facilitates asynchronous and persistent workflows.
Operate without exposing internal state: Agents can interact without revealing their internal memory or tools.
Key features of the A2A .NET SDK include:
Agent Capability Discovery: Utilizes the A2ACardResolver class to retrieve agent capabilities described in standardized Agent Cards, providing essential information such as host URL, image, supported modalities, and streaming capabilities.
Flexible Communication Patterns: Supports both direct, synchronous message-based communication for immediate responses and persistent, long-running task-based communication for asynchronous workflows.
Real-time Streaming Support: Provides comprehensive streaming capabilities using Server-Sent Events for scenarios requiring real-time updates.
ASP.NET Core Integration: Simplifies the process of building A2A-compatible agents with included ASP.NET Core extensions, allowing developers to expose their agents via the A2A protocol with minimal code.
The SDK is currently in preview, indicating that while Microsoft aims for stability, the API may undergo changes based on community feedback and protocol evolution. Microsoft encourages contributions, feedback, and community involvement, as the A2A .NET SDK is open source and available under the Apache 2.0 License.
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This release marks a significant step towards a future where AI applications are not just about user-agent interactions but also about complex, collaborative networks of intelligent agents working together to solve more sophisticated problems. Developers are encouraged to explore samples, the GitHub repository, and resources related to Azure AI Foundry and Semantic Kernel to further their journey in building advanced A2A agents.
