format-css

Fast, small, zero-config library to format CSS with basic rules. The design goal is to format CSS in a way that makes it easy to inspect. Bundle size and runtime speed are more important than versatility and extensibility.

Example output

/* TURN THIS: */

@layer base.normalize{@media (dynamic-range:high) or (color-gamut:p3){@supports (color:color(display-p3 0 0 0)){:where(html){--link:color(display-p3 .1 .4 1);--link-visited:color(display-p3 .6 .2 1)}}}}@layer base.normalize{:where(html) :where(dialog){background-color:var(--surface-1)}}

/* INTO THIS: */

@layer base.normalize {
	@media (dynamic-range: high) or (color-gamut: p3) {
		@supports (color: color(display-p3 0 0 0)) {
			:where(html) {
				--link: color(display-p3 .1 .4 1);
				--link-visited: color(display-p3 .6 .2 1);
			}
		}
	}
}

@layer base.normalize {
	:where(html) :where(dialog) {
		background-color: var(--surface-1);
	}
}

/* AND BACK AGAIN! */

Installation

npm install @projectwallace/format-css

Usage

import { format } from '@projectwallace/format-css'

let old_css = '/* Your old CSS here */'
let new_css = format(old_css)

Need more examples?

• StackBlitz example using CommonJS
• StackBlitz example using ES Modules

Partial formatters

The package also exports lower-level formatters for individual CSS constructs:

import {
	format_value,
	format_declaration,
	format_selector,
	format_atrule_prelude,
} from '@projectwallace/format-css'

// Format a CSS value (e.g. the right-hand side of a declaration)
format_value(node.value)

// Format a single CSS declaration (property + value)
format_declaration(node)

// Format a single CSS selector
format_selector(node)

// Format an at-rule prelude string (e.g. the query part of @media)
format_atrule_prelude(node.prelude.text)

All of these accept the same options as format(). However, tab_size has no effect on them since they do not produce indented output.

format_declaration(node, { minify: true })
format_selector(node, { minify: true })

Formatting rules

1. Every AtRule starts on a new line
2. Every Rule starts on a new line
3. Every Selector starts on a new line
4. A comma is placed after every Selector that’s not the last in the SelectorList
5. Every Block is indented with 1 tab more than the previous indentation level
6. Every Declaration starts on a new line
7. Every Declaration ends with a semicolon (;)
8. An empty line is placed after a Block unless it’s the last in the surrounding Block
9. Multiline tokens like Selectors, Values, etc. are rendered on a single line
10. Unknown syntax is rendered as-is, with multi-line formatting kept intact

Options

Minify CSS

This package also exposes a minifier function since minifying CSS follows many of the same rules as formatting.

import { format, minify } from '@projectwallace/format-css'

let minified = minify('a {}')

// which is an alias for

let formatted_mini = format('a {}', { minify: true })

Tab size

For cases where you cannot control the tab size with CSS there is an option to override the default tabbed indentation with N spaces.

import { format } from '@projectwallace/format-css'

let formatted = format('a { color: red; }', {
	tab_size: 2,
})

CLI

This library also ships a CLI tools that's a small wrapper around the library.

USAGE
  format-css [options] [file...]
  cat styles.css | format-css [options]

OPTIONS
  --minify            Minify the CSS output
  --tab-size=<n>      Use N spaces for indentation instead of tabs
  --help, -h          Show this help

EXAMPLES
  # Format a file
  format-css styles.css

  # Format with 2-space indentation
  format-css styles.css --tab-size=2

  # Minify
  format-css styles.css --minify

  # Via pipe
  cat styles.css | format-css

Related projects

• Format CSS online - See this formatter in action online!
• Minify CSS online - See this minifier in action online!
• CSS Analyzer - The best CSS analyzer that powers all analysis on projectwallace.com