@vcalderondev/ukit-css

JIT utility-first CSS engine — Tailwind-style on-demand class generation for any frontend stack (React, Vue, Angular, Svelte, Next.js, Astro, plain HTML).

ukit-css is a powerful Node + TypeScript engine that scans your source files, extracts the classes you actually use, and emits only those as CSS. It supports rich utility class names (m-1-rem, grid-cols-3-m, rounded-lg, text-ellipsis-3, …) while dropping your bundle size to the absolute minimum.

Why JIT?

Mode	Output	Notes
Legacy (Static CSS)	~770 KB compiled & minified	Every utility shipped, used or not
JIT (ukit-css)	typically 2–30 KB per project	Only the classes you actually reference

In a real project that uses 46 distinct utilities across HTML/JSX/Vue templates, the engine emits ~2.4 KB minified — a 99.7% reduction versus static utility libraries.

Installation

npm install -D @vcalderondev/ukit-css

Quick start (CLI)

Create a configuration file at the root of your project:

// ukit.config.mjs
export default {
  content: ["./src/**/*.{html,js,jsx,ts,tsx,vue,svelte,astro}"],
  output: "./dist/ukit.css",
}

Then build:

npx ukit-css build

Or watch for changes during development:

npx ukit-css watch

Add --minify for production builds, --output to override the destination, or --content to override globs from the command line.

Integration recipes

Vite (React / Vue / Svelte / vanilla)

// vite.config.ts
import { defineConfig } from "vite"
import ukit from "@vcalderondev/ukit-css/vite"

export default defineConfig({
  plugins: [ukit()],
})

// main.ts (or main.tsx)
import "virtual:ukit.css"

HMR is wired in: every time you touch a content file, the virtual stylesheet rebuilds and hot-reloads instantly.

PostCSS (Next.js, Angular, Nuxt, Astro, Webpack, anywhere)

// postcss.config.mjs
import ukit from "@vcalderondev/ukit-css/postcss"

export default {
  plugins: [ukit()],
}

/* src/styles/app.css */
@ukit;

The @ukit; at-rule is expanded to the JIT output. If you omit it, the plugin prepends the CSS to the entry file automatically.

Next.js (without a custom PostCSS plugin)

Use the CLI in a script and import the generated file:

// package.json
{
  "scripts": {
    "css:build": "ukit-css build -o app/ukit.css --minify",
    "css:dev":   "ukit-css watch -o app/ukit.css"
  }
}

// app/layout.tsx
import "./ukit.css"

Angular

// angular.json (excerpt)
{
  "styles": ["src/ukit.css", "src/styles.scss"]
}

# during development
npx ukit-css watch -o src/ukit.css
# before production build
npx ukit-css build -o src/ukit.css --minify

Plain HTML

npx ukit-css build --content "./public/**/*.html" -o ./public/ukit.css --minify

<link rel="stylesheet" href="/ukit.css" />

---

Configuration

// ukit.config.mjs (or .js / .cjs / .json)
import { defineConfig } from "@vcalderondev/ukit-css"

export default defineConfig({
  // Globs scanned for class candidates. The engine reads each file as text
  // and pulls out any token that could be a utility class — so it works with
  // Angular [class.x], Vue :class, React clsx(), Svelte class:foo, etc.
  content: ["./src/**/*.{html,ts,tsx,vue,svelte}"],

  // Output path (used by the CLI). Plugins ignore this.
  output: "./dist/app.css",

  // Breakpoint overrides.
  mobile: 576,
  tablet: 992,
  desktop: 1200,

  // Toggle the CSS reset + the keyframes block.
  preflight: true,
  keyframes: true,

  // Class names to always include even if they don't appear in source files
  // (useful for classes that are composed dynamically: `m-${size}-rem`, etc.).
  safelist: ["m-1-rem", "m-2-rem", "m-3-rem"],

  // Minify the output.
  minify: false,
})

---

Utility reference

Every utility ships with a base, -m (mobile, ≤ 576 px) and -t (tablet, 577–992 px) variant.

Category	Examples
Display	d-flex, d-grid, d-none-m
Sizing	w-50, h-100vh, min-w-200px, max-w-90
Spacing	m-1-rem, pt-16px, gap-1-5-rem, mx-auto
Position	position-absolute, top-50-percent, left-50-percent, translate-center
Flex	align-items-center, justify-content-between, flex-direction-column
Typography	fs-1-rem, fw-700, text-center, lh-1-5, text-ellipsis-3
Borders	rounded-lg, rounded-r-12px, border, border-t, border-none
Grid	grid-cols-3, grid-cols-1-m, grid-col-span-2, grid-row-span-full
Z-index	z-1, z-50, z-9999
Opacity	opacity-50, opacity-0
Overflow	overflow-hidden, overflow-x-auto
Animate	animate-fade-in, animate-fade-in-up, animate-spin, animate-pulse

Naming convention (spacing): {prop}{dir?}-{value}[-{unit}][-{breakpoint}]. Example: pt-1-5-rem-m → padding-top: 1.5rem on mobile.

For the full vocabulary refer to the matchers in src/core/matchers/ — each file documents the patterns it recognizes.

---

Programmatic API

import { build, Engine, defineConfig } from "@vcalderondev/ukit-css"

// One-shot build
const { css, matchedClasses } = await build({
  content: ["./src/**/*.tsx"],
})

// Long-lived engine (incremental rebuilds, watch mode, plugins)
const engine = new Engine({ content: ["./src/**/*.tsx"] })
await engine.scanAll()
const { css: output } = engine.build()

License

MIT — Victor Calderon mail@vcalderon.dev