PresetCSS

A utility-first CSS framework with a radically simpler configuration system. One flat preset file in, one CSS file out compiled by a single Rust binary. No JavaScript config, no extend merge magic, no plugin system for the 90% case.

# preset.toml - this is the whole config
[colors]
primary = "#3b82f6"
[breakpoints]
tablet = "768px"

/* generated */
.bg-primary { background-color:#3b82f6; }
.text-primary { color:#3b82f6; }
.border-primary { border-color:#3b82f6; }
@media (min-width:768px) { .tablet\:flex { display: flex; } }

Install / build

cargo build --release # binary at target/release/presetcss
cargo install --path crates/presetcss-cli

Commands

Command	What it does
presetcss init	Write a commented preset.toml (a copy of the defaults).
presetcss build [--minify] [--verbose] [-c file] [-o out.css]	Generate CSS.
presetcss watch	Build, then rebuild on changes to the preset or content files.
presetcss validate	Check the preset for typos, bad hex, key collisions - no output written.
presetcss explain <class>	Show the CSS and preset provenance for one class.
presetcss export --format json|js|css-vars	Export design tokens.
presetcss help theme / help static	List token keys / built-in static utilities.

How config works (the only rule you must learn)

• A token group like [colors] is a flatkey = "value" map. No nesting.
• Writing [colors]replaces the default color group.
• [extend.colors]adds to it (your keys win). That is the only merge.
• Variants are opt-in per group under [variants] - nothing is implicit.
• Need a one-off rule? [utilities] takes raw CSS. Still no JavaScript.

[extend.colors] # keep defaults, add one colorbrand = "#ff0050"
[variants] # only colors get hover/focus; statics get breakpointscolors = ["hover", "focus"]
static = ["responsive"]
[utilities]
btn = "padding: 0.5rem 1rem; border-radius: 6px; background: #3b82f6; color: white;"

Variant syntax

breakpoint:state:utility - e.g. tablet:hover:bg-primary. Breakpoint names are yours (from [breakpoints]), not a fixed sm/md/lg.

Tree-shaking

Set content = ["src/**/*.html"] in [options] and build emits only the classes it finds in those files. Near-misses are reported instead of silently dropped: 'bg-primry' looks like a PresetCSS class but is not generated - did you mean 'bg-primary'?

Project layout

crates/presetcss-core/ # pure library: parse -> resolve -> [scan] -> generate -> emit
crates/presetcss-cli/ # the `presetcss` binary
examples/ # minimal + advanced presets
DESIGN.md # full design document

Develop

cargo test# core has a snapshot-style unit suite
cargo clippy --all-targets

License

GPL-3.0 © Seyyed Ali Mohammadiyeh (MAX BASE)