Does this send my code anywhere?

No. Compilation runs entirely in your browser using less.js, the same library that historically compiled LESS in-browser.

Does this support @import from other files?

No. Only self-contained LESS with no external file imports is supported.

Does this support LESS features like mixins and operations?

Yes. `less.render()` compiles the full LESS language, variables, nesting, mixins, guards, and math operations, the same as a normal LESS build would. The only thing missing is resolving `@import` of separate files, since there's no filesystem here.

How is LESS different from Sass, functionally?

Both compile a CSS-superset language with variables, nesting, and mixins down to plain CSS. LESS variables use `@` and Sass uses `$`, and their mixin and function syntax differs, but for a single self-contained stylesheet like the ones this tool compiles, the concepts map closely.

LESS Compiler - Compile LESS to CSS Online

Overview

Introduction

LESS's variables, nesting, and mixins need to compile down to plain CSS before a browser can use them.

This tool compiles LESS to CSS directly in your browser using less.js, the official compiler.

What Is LESS Compiler?

A LESS-to-CSS compiler using `less.render()`, the same engine that ships as the `less` npm package.

It compiles self-contained LESS: variables, nesting, and mixins all resolve to plain CSS.

How LESS Compiler Works

less.js parses the LESS source and resolves nesting, variables, and mixins into flat CSS rules.

A syntax error is reported with its line and column.

When To Use LESS Compiler

Use it to quickly preview what a LESS snippet compiles to without setting up a build pipeline.

It's also useful for converting an old LESS-based stylesheet to plain CSS, or checking whether a specific mixin or operation compiles the way you expect.

Often used alongside Sass Compiler and CSS Formatter.

Features

Advantages

Runs entirely client-side.
Uses less.js, the reference LESS implementation, so output matches what a real LESS build produces.
Reports the line and column of a compile error, useful for tracking down a missing semicolon or a malformed mixin call.

Limitations

No `@import` of external files, since there's no filesystem for the compiler to resolve paths against.

Examples

Nesting and variables

Input

@color: #333;
.card {
  color: @color;
  .title { font-weight: bold; }
}

Output

.card {
  color: #333;
}
.card .title {
  font-weight: bold;
}

The variable is substituted and the nested selector is flattened into a descendant combinator.

Best Practices & Notes

Best Practices

Keep snippets self-contained (no external imports) since this tool compiles a single pasted string.
Check the compiled CSS's selector nesting; deeply nested LESS can generate long, over-specific selectors that are easy to miss while only reading the source.

Developer Notes

Uses `less.render(input)` from the `less` package's browser build, dynamically imported.

LESS Compiler Use Cases

Previewing what a LESS snippet compiles to
Converting a small self-contained LESS file to plain CSS

Common Mistakes

Pasting LESS with `@import` of another file and expecting it to resolve, since no filesystem is available.
Mixing units in arithmetic (e.g. `10px + 2em`) and expecting LESS to convert between them automatically.

Tips

Inline any variables or mixins you'd normally import from another file before pasting.
When a math expression isn't producing the expected value, check that both operands share the same unit; LESS's arithmetic can behave unexpectedly across mismatched units.

LESS Compiler