{"id":60832,"date":"2026-09-16T14:00:00","date_gmt":"2026-09-16T21:00:00","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/dotnet\/?p=60832"},"modified":"2026-09-29T11:46:41","modified_gmt":"2026-09-29T18:46:41","slug":"build-your-own-ai-agent-harness-in-csharp-the-maf-claw-live-series","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/dotnet\/build-your-own-ai-agent-harness-in-csharp-the-maf-claw-live-series\/","title":{"rendered":"Build Your Own AI Agent Harness in C#, the MafClaw Live Series"},"content":{"rendered":"

A few weeks ago I wrote about going from dotnet run<\/code> to a Foundry Hosted Agent in three lines of C#<\/a>. The feedback was great. Developers liked the deployment story, the managed infrastructure, and especially the part where we did not<\/strong> spend the afternoon writing a Dockerfile, a session store, a telemetry pipeline, and a small distributed system just to expose one agent \ud83d\ude05.<\/p>\n

But that post starts near the end of the journey. It assumes you already have an agent worth deploying.<\/p>\n

So the next question is:<\/p>\n

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“What should I put inside the agent before I deploy it?”<\/p>\n<\/blockquote>\n

Tools. Planning. Safe file access. Human approval. Memory. Skills. Shell commands. Code execution. Background agents. Observability. Governance. Evaluations.<\/p>\n

That list gets big very quickly.<\/p>\n

The good news is that you do not need to build the runtime for all of it from scratch. Microsoft Agent Framework includes an agent harness<\/strong>, and I am building a complete C# agent with it live, one capability at a time, in a four-part series called From Model to Agent: The Agent Framework Harness, Live in C#<\/strong>.<\/p>\n

The series streamed live simultaneously on the .NET YouTube channel<\/a><\/strong> and Microsoft Reactor over four Thursdays in September. All four sessions are now available on demand, along with the complete C# sample repository, the audience slides, and the session guides. Let me show you what we built and why the harness makes this much easier.<\/p>\n

Watch the complete Agent Framework series<\/a><\/div><\/p>\n

What we build across four sessions<\/h2>\n

We start with this:<\/p>\n

AIAgent agent = chatClient.AsHarnessAgent(new HarnessAgentOptions\n{\n    ChatOptions = new ChatOptions\n    {\n        Instructions = instructions,\n        Tools = tools\n    }\n});<\/code><\/pre>\n
Then we grow the same agent through four stages:<\/p>\n
    \n
  1. Give it tools, web search, and a plan.<\/li>\n
  2. Let it work with files, approvals, and durable memory.<\/li>\n
  3. Add skills, shell, CodeAct, and background agents.<\/li>\n
  4. Add observability, governance, evaluations, and a hosted deployment.<\/li>\n<\/ol>\n
    That is the complete journey: from one call around an IChatClient<\/code> to a capable agent that we can inspect, evaluate, govern, and run in Microsoft Foundry.<\/p>\n
    First: what is an agent harness?<\/h2>\n
    A language model can generate text. An agent needs more.<\/p>\n
    It needs a loop that can call tools, inspect the results, update a plan, remember useful information, request approval for risky actions, manage a growing context window, and keep working until the task is complete.<\/p>\n
    That surrounding runtime is the harness<\/strong>.<\/p>\n
    <\/i>Where the term comes from<\/strong><\/p>The Microsoft Agent Framework team introduced the concept in the excellent Build your own claw and agent harness with Microsoft Agent Framework<\/a> series. Their explanation is simple: a “claw” is a CLI-style agent built on top of a harness. You bring the model, instructions, and domain tools. The harness supplies the agentic machinery around them.<\/div><\/p>\n
    In .NET, the key line is this one:<\/p>\n
    AIAgent agent = chatClient.AsHarnessAgent(new HarnessAgentOptions\n{\n    ChatOptions = new ChatOptions\n    {\n        Instructions = \"You are a personal finance education assistant.\",\n        Tools = [StockTools.GetStockPrice]\n    }\n});<\/code><\/pre>\n
    That call gives the agent a complete pipeline with capabilities such as:<\/p>\n