Scarlet.Sass.Cli 1.105.0

Scarlet.Sass.Cli

Run Dart Sass — the reference implementation of Sass — as a .NET tool.

dotnet sass --version
dotnet sass Sass:wwwroot/css --style=compressed

Every argument is forwarded to Dart Sass verbatim, so anything valid after sass is valid after dotnet sass.

Why not just install Dart Sass?

You still can — nothing here stops you, and for a solo project with no CI this buys you little. It earns its keep once a repository has more than one contributor or a CI pipeline, because it makes Dart Sass pinned and installed the same way as the rest of your .NET tooling, instead of a separate step with its own installer:

• Pinned like everything else. The Dart Sass version lives in .config/dotnet-tools.json next to dotnet-ef, dotnet-format, and friends. dotnet tool restore brings it down with the repository — no "works on my machine because I have Sass 1.105 and CI has 1.100."
• Hash-verified. NuGet checks the package against what it published, unlike a curl | sh installer.
• No network at run time, for the platform-specific package — it contains the official Dart Sass bundle, so there's no download on first use, no dependency on github.com being reachable, and no chance of a CI agent quietly picking up a different Sass than your laptop did.

Install

Per repository (recommended — this is the part that pins):

dotnet new tool-manifest      # once per repository
dotnet tool install Scarlet.Sass.Cli
dotnet sass --version

Commit .config/dotnet-tools.json and every contributor and CI agent gets the same Dart Sass from dotnet tool restore.

Globally:

dotnet tool install -g Scarlet.Sass.Cli

Or once, without installing anything (.NET 10 SDK):

dnx Scarlet.Sass.Cli -- Sass:wwwroot/css --style=compressed

The package version is the Dart Sass version. Scarlet.Sass.Cli 1.104.1 contains Dart Sass 1.104.1, the same as the Scarlet.Sass.Runtime.* packages.

To move to a newer Dart Sass, update the package like any other .NET tool — no separate upgrade command needed:

dotnet tool update Scarlet.Sass.Cli      # local: also bumps .config/dotnet-tools.json
dotnet tool update -g Scarlet.Sass.Cli   # global

How it finds Dart Sass

Scarlet.Sass.Cli is a pointer package: it owns the dotnet-sass command but carries no Dart Sass bundle itself. Installing it makes dotnet tool install/dotnet tool restore also pull one matching sub-package for your machine's RID — Scarlet.Sass.Cli.win-x64, Scarlet.Sass.Cli.linux-arm64, and so on — and that package embeds the official dart-sass folder. This is automatic; you never name a sub-package yourself, and running dotnet add package Scarlet.Sass.Cli.<rid> on one directly installs nothing usable — it carries no library assets, only a tool payload NuGet places when Scarlet.Sass.Cli asks for it.

Supported platforms are Windows, Linux and macOS on x64 or arm64, including musl-based Linux distributions such as Alpine — one sub-package per combination, eight in total. Hosts outside that matrix restore Scarlet.Sass.Cli.any instead: a portable fallback with no embedded runtime, so it downloads Dart Sass on first use and caches it per user rather than shipping a mismatched one. Any other architecture gets an explanatory error rather than a mismatched runtime — install Dart Sass separately and point at its launcher with SCARLET_SASS_PATH if you need one.

Resolution order:

1. SCARLET_SASS_PATH, if set — errors if it points at nothing, rather than quietly falling back
2. the Dart Sass bundle embedded in the installed package
3. a previously downloaded Dart Sass bundle in the per-user cache
4. a download

To see what it chose and why:

dotnet sass --scarlet-info
dotnet sass --scarlet-info --json

That is the only argument the tool reserves for itself, it is recognised only as the first argument, and SCARLET_SASS_PASSTHROUGH=1 disables even that. It never downloads anything — it reports the URL it would use.

Configuration

Configuration is environment variables rather than command-line flags on purpose: every argument belongs to Dart Sass, so a flag Sass adds in future keeps working without a release of this package.

SCARLET_SASS_VERSION changes which Dart Sass runtime gets downloaded and run — it never changes which NuGet package is installed; that's decided once, at dotnet tool install time (see How it finds Dart Sass). Setting it to anything other than the version baked into the installed package skips the embedded runtime and downloads the requested one into the per-user cache, scoped by version (<cache>/runtimes/<version>/), so later runs with the same value reuse it instead of re-downloading.

That caching applies to latest too, literally: the first run resolves whatever GitHub currently tags as newest and caches it under a folder named latest, and every run after that reuses that cached runtime without checking GitHub again — latest means "newest at the time I first asked," not "always current." Clear <cache>/runtimes/latest/ (or point SCARLET_SASS_CACHE elsewhere) to pick up a newer release.

Running Dart Sass during a build instead

If you want Sass to run as part of dotnet build and have its CSS included in ASP.NET Core, Blazor or Razor Class Library static web assets, use Scarlet.Sass.MSBuild instead. The two are independent; this tool is for the command line.

Links

• Source and full documentation
• Dart Sass documentation

Licensed under MIT. Dart Sass itself is licensed separately — see the Dart Sass repository.