FieldCure.ToolHost

Run .NET tools from NuGet without the .NET SDK — a dnx-compatible bridge for runtime-only environments (MS Store apps, MSIX-distributed software, runtime-only containers, CI bootstrappers).

This is a time-bounded bridge until Microsoft ships standalone dnx (tracking dotnet/sdk#49796). When that ships, this project enters maintenance and eventually deprecation. The API and CLI intentionally mirror dnx so migration is mechanical. See ROADMAP.md.

Why

dnx is excellent — but it ships only with the .NET 10 SDK. If your software is distributed through channels where users may have only the .NET runtime (the Microsoft Store, MSIX installers, runtime-only Docker images, etc.), dnx is unavailable. FieldCure.ToolHost fills that gap with the same UX.

Prerequisites

This is a tool runner, not a runtime distributor. A .NET 8 or .NET 10 runtime must be present on the host — ToolHost discovers the dotnet muxer through PATH or DOTNET_ROOT and uses it to launch tools. It deliberately does not ship a runtime of its own.

If you are shipping software to environments where users may not already have a runtime (fresh PCs receiving your MS Store app, minimal Docker images, etc.), you are responsible for bundling one alongside your application or guiding the user to install it. ToolHost's job ends at "find and use the runtime that's available."

Two ways to use it

As a library (primary)

using FieldCure.ToolHost;
using System.Diagnostics;

DotnetEnvironment env = await DotnetEnvironment.DetectAsync();
DnxLiteRunner runner = new(env);

using Process tool = await runner.StartAsync(new ToolInvocationRequest
{
    PackageId = "dotnetsay",
    ToolArguments = new[] { "Hello from a runtime-only host!" },
    Policy = ToolVersionPolicy.CachedWithRefresh,
});

tool.StandardInput.Close();
string output = await tool.StandardOutput.ReadToEndAsync();
await tool.WaitForExitAsync();
Console.WriteLine(output);

As a CLI (fcdnx)

dotnet tool install -g FieldCure.ToolHost.Cli

fcdnx dotnetsay
fcdnx dotnetsay@2.1.0
fcdnx --prerelease MyTool.Preview
fcdnx --add-source https://feed.example.com/v3/index.json MyCorp.Tool

See docs/flag-compatibility.md for the full flag matrix.

Scope

In scope:

• Library + CLI (fcdnx) with full dnx flag parity for the v0.1 surface
• NuGet global packages folder reuse (interoperates with dotnet/dnx)
• Three resolution policies: AlwaysLatest, CachedWithRefresh, CachedOnly
• Authenticated feeds via standard NuGet credential providers
• Platform-agnostic .NET tools (tools/{tfm}/any/)
• Opt-in child-process environment isolation for hosts that run untrusted tools or MCP servers

Out of scope and staying that way:

• Tool installation/uninstallation (dotnet tool install/update/uninstall)
• Replacing or wrapping the dotnet muxer
• Features outside dnx parity, except narrow host-safety controls such as environment inheritance isolation

See the Lifecycle / Sunset Policy section of ROADMAP.md. Feature requests outside dnx parity will be politely closed.

Status

• v0.1 — MVP: resolution + extraction + launch for managed tools, CLI parity for the core flag set, NuGet credential plumbing.
• v0.2 — Platform-specific tools (RID graph traversal), self-contained / NativeAOT tools, expanded authenticated-feed test matrix.
• v1.0 — API frozen, breaking changes require major bumps.

Contributing

See CONTRIBUTING.md. Please read the scope discipline statement before opening a feature PR.

License

MIT — see LICENSE.