MonorailCss

This is the human-readable landing page. If you're an LLM or other automated consumer, fetch /llms.txt instead — it's a structured index of every doc page with per-page markdown sidecars at /_llms/...md. The marketing UI below is not visible to you in extraction.

What MonorailCss does

A JIT CSS compiler for .NET that aims to be Tailwind CSS 4.2 compatible. Hand CssFramework.Process a list of utility class names and it returns the CSS those classes need — including theme variables, preflight reset, variants, breakpoints, dark mode, arbitrary [value]s, opacity modifiers, and trailing ! for important. In-process, no Node toolchain.

Install

dotnet add package MonorailCss

Hello world

using MonorailCss;

var framework = new CssFramework();
var css = framework.Process("flex gap-4 p-6 bg-blue-500 text-white");

Where to go next

/llms.txt — structured index of the whole site for LLMs.
Getting started — installation, first stylesheet, variants, important, arbitrary values.
API reference — public types and method signatures populated from xmldoc.
/utility/llms.txt — every utility class grouped by category, with the generated CSS.

Tailwind 4.3 · JIT · Pure C#

Ship Tailwind CSS without the toolchain.

MonorailCSS is a Tailwind-compatible JIT compiler written in pure .NET. Compile utilities at runtime, in-process, with zero npm.

Get started View on GitHub ↗

0 npm deps

~12ms cold compile

1.4k+ utilities

9, 10 .NET versions

Program.cs C#

using MonorailCss;

// 1. configure once
var framework = new CssFramework();

// 2. point it at your markup
var css = framework.Process("flex gap-4 p-6 bg-primary-500");

// 3. ship the bytes
File.WriteAllText("site.css", css);

Compiled 4 utilities in 11ms

Works with ASP.NET Core · Blazor · Razor Pages · MAUI

◆Why MonorailCSS

A first-class CSS pipeline, in the language you already use.

Every feature you expect from Tailwind, expressed as idiomatic .NET. No build orchestration, no JS dependencies, no cognitive context-switch.

.NET-native, end to end

Pure C# — no Node, no shelling out, no JS interop. Reference a NuGet package and compile inline.

Tailwind 4.3 compatible

Same utility names, same variants, same arbitrary-value syntax. Bring your existing markup unchanged.

Just-in-time

Scans your content, emits only what you used. Cold compiles in ~12ms; hot rebuilds are sub-millisecond.

Built for ASP.NET

Drop-in middleware for runtime CSS, hot reload under dotnet watch, source-generator-friendly.

Theme-able by config

Override colors, spacing, breakpoints with a single ITheme. Add custom utilities and variants from C#.

Tiny & dependency-free

One assembly, zero external runtime deps. AOT-friendly. Trims well. Ships clean.

◆Try it

Type utilities. Watch CSS appear.

The same JIT engine that powers your build, running in your browser. Edit the input — the compiled CSS updates live.

Input — utility classes

flex items-center gap-4 px-6 py-4 rounded-xl bg-primary-600 text-white hover:bg-primary-700

Preview

Preview element

Output — generated CSS ● 23 lines · ~7ms

.flex {
  display: flex;
}
.items-center {
  align-items: center;
}
.gap-4 {
  gap: 1rem;
}
.px-6 {
  padding-inline: 1.5rem;
}
.py-4 {
  padding-block: 1rem;
}
.rounded-xl {
  border-radius: 0.75rem;
}
.bg-primary-600 {
  background-color: oklch(56% 0.129 52.073);
}
.text-white {
  color: #fff;
}
.hover\:bg-primary-700:hover {
  background-color: oklch(49% 0.118 52.073);
}

◆Get going

Three steps from dotnet add to shipping CSS.

Install the NuGet package, instantiate the framework, and you're generating utility CSS at runtime.

01 Add the package

dotnet add package MonorailCss

02 Create a framework

var fx = new CssFramework();
var css = fx.Process("p-6 bg-primary-500");

03 Wire it up

app.UseMonorail(opts => {
    opts.ContentRoots = ["Pages", "Views"];
});

Open source · MIT

Bring Tailwind home to .NET.

Read the docs, scan the source, file an issue. Contributions welcome.

Read the docs View on GitHub ↗