Fadenstack .NET SDK¶

This page introduces the .NET SDK, its packages and target frameworks, and shows how to add it to a project.

What the SDK is¶

The SDK builds agents that run inside other software and are governed by a Fadenstack server. The host can be a desktop application such as EPLAN, TIA Portal or Microsoft Office, a Windows service or a console tool.

The work is split between the device and the server. The device runs the agent loop: it sends the conversation, runs the host application's tools, asks the user before a tool changes something, attaches local MCP servers and keeps the conversation. The server owns the agent's instructions, its model and its knowledge, and it handles personal data (PII) and the audit trail. Budgets are Planned.

The SDK never receives the agent's instructions. Every model call goes through the server's gateway, which applies the organisation's policies on the way to the model and back. Agents on the server explains how an agent is defined there.

Packages¶

Each package brings the packages it builds on. Faden.Agents includes Faden.Client; Faden.Mcp and Faden.UI include Faden.Agents; Faden.UI.Wpf includes Faden.UI.

Target frameworks¶

The netstandard2.0 builds serve .NET Framework hosts, such as add-ins loaded by a native application. A .NET 8 or later application gets the net8.0 builds. If you write a library on top of the SDK, read Building a library first.

Install¶

The packages are published to NuGet with the first release. Until then, reference the projects from source.

1. Clone the repository next to your solution:

   git clone https://github.com/fadenstack/fadenstack-sdk-dotnet.git
   

2. Reference the project of each package you need from your project file:

   <ItemGroup>
     <ProjectReference Include="..\fadenstack-sdk-dotnet\src\Faden.Agents\Faden.Agents.csproj" />
   </ItemGroup>
   

   For local MCP servers, add src\Faden.Mcp\Faden.Mcp.csproj. For the WPF chat panel, add src\Faden.UI.Wpf\Faden.UI.Wpf.csproj.

Build the SDK's projects with the .NET 10 SDK. Your own project can target any of the frameworks in the table above.

A complete example¶

A console program that signs in to an agent, offers one host tool and asks one question:

using System.ComponentModel;
using Faden;
using Faden.Agents;
using Faden.Tools;

using var client = FadenClient.ForAgent(new Uri("https://ai.example.internal"), "my-assistant", out var tokens);
if (!await tokens.IsSignedInAsync())
{
    // First run only: the sign-in is kept for this user on this device.
    await tokens.SignInAsync(loginToken: args[0], deviceLabel: "Console on " + Environment.MachineName);
}

using var agent = FadenAgent.CreateBuilder()
    .UseClient(client)
    .UseAgent("my-assistant")
    .AddTools(new PageTools())
    .Build();

var session = await agent.StartSessionAsync();
var result = await session.SendAsync("What is on page 7?");
Console.WriteLine(result.Text);
Console.WriteLine($"Outcome: {result.Outcome}");

public sealed class PageTools
{
    [AgentTool(ToolClass.Read), Description("Reads a page of the open document.")]
    public string ReadPage(int page) => $"Page {page}: contactor K1, terminal strip X1.";
}

read_page is a read tool, so it runs without asking in the mode every session starts in. A tool that changes something asks the user first, and without an approval handler such a call is declined. Host tools explains both.

Namespaces¶

Where next¶

• Build an agent: the client, sign-in, the builder, sessions and streaming.
• Host tools: tools, tool modes and approvals.
• Outcomes and errors: how a turn ends, and what is thrown.
• Sessions on the device: storage, retention and your own store.
• Chat panel: a ready chat UI for WPF hosts.
• Your first agent: registering an agent on the server and signing in.
• TypeScript SDK: the same agents, built in TypeScript.