Building Your First AI Agent with .NET and Azure AI Foundry

If you're a .NET developer looking to break into AI engineering, agents are the single best place to start. They're the point where "calling an LLM API" turns into "building a system that reasons, uses tools, and takes action" — and Azure AI Foundry Agent Service, paired with .NET, makes this surprisingly approachable. In this post, I'll walk through exactly how to stand up your first agent end-to-end — from the Azure side setup to the actual C# code — and share the full walkthrough in video form as well. 🎥 Watch the full hands-on video here: https://youtu.be/mrsEsculrNg Why Agents, and Why Now Most of us started our AI journey with a simple chat completion call — send a prompt, get text back. That's fine for Q&A, but it falls apart the moment you need the model to do something: run code, search documents, call an API, or hold a multi-turn conversation with real state. That's exactly the gap Foundry Agent Service closes. An agent in Foundry is: Durable — it lives as a resource in your Foundry project, not in your app's memory Tool-aware — it can invoke built-in tools (like a code interpreter) or your own custom functions Stateful — conversations persist and carry context across turns And the best part for us .NET folks: the entire thing is callable from clean, typed C# — no wrestling with raw REST payloads. What You'll Need Before writing any code, set up the Azure side: An Azure AI Foundry project with a chat model deployed (e.g., gpt-4o-mini ) The Foundry User RBAC role assigned to your account at the resource/resource-group scope — this is the single most common blocker people hit (a silent 403 when calling the SDK), so don't skip it az login run locally, so your code can authenticate without hardcoding any keys If you've worked with Cognitive Services roles before, note that agent management needs this separate Foundry-specific role — that trips up a lot of people coming from plain Azure OpenAI usage. Setting Up the .NET Project dotnet new console -n FoundryAgen