Less for Sass developers

I’m a Sass fan. I’ve used it for the last couple of years now and would use it on every project if I had the choice. However, as a contractor, I’ve had the opportunity (been forced) to use numerous productivity tools such as pre-processors on a range of projects.

Currently I’m working for an agency that uses both Sass and Less - they initially used Less but are transitioning into Sass for some projects. I’m currently stuck on one of their legacy project so have had the chance to try my hand at the “other” pre-processor for the last couple of weeks.

First impressions

While I prefer Sass, I don’t want this post to become a Less-bashing one. To be brutally honest, the two tools are pretty much the same these days and they both make writing CSS easier, more powerful and more fun.

The most notable thing is a difference in syntax - but even then, the differences are minor. It was incredibly quick to get used to - doing the same things and working (mostly) the same way I’m used to, just with different syntax.

What do they share?

As far as I could tell within the boundaries of a fairly simple project, Less and Sass both have the following features in common:

  • Variables
  • Nesting
  • Interpolation
  • Parent selectors
  • Math
  • @import to concatenate multiple files
  • Mixins
  • Extend (sort of)
  • Custom Functions (sort of)
  • Built in functions
  • Loops (recursive mixins in Less)

How are they different?

Instead of going into lengthy descriptions about all the differences, I thought I’d cut to the chase and provide a side-by-side comparison of the syntax. The Sass will be first, the Less will be second. Here goes:


$color-pink: #cc3f85;
a { 
	color: $color-pink;
@color-pink: #cc3f85;
a { 
	color: @color-pink;

Sass uses the $ sign to create a variable, Less uses the @ symbol. I’m not keen on Less’ choice to use @ as it’s already used in vanilla CSS to mark a block rule like @media or @supports.


These are the same in both languages. Nesting selectors reduces the amount you need to type but I always like to keep the number of levels to a minimum.

.nav-primary {
	li {

		&:hover .sub-menu {
// outputs
// .nav-primary li { display:inline-block; }
// .nav-primary li:hover .sub-menu { display:block; }

The & character is used to reference the parent selector - both Sass and Less have this feature too.


Interpolation allows a variable value to be used as a selector name or as part of an image path. The major difference is the placement of the variable token $ or @.

$selector: 'carousel';
.#{$selector} {
// outputs .carousel { display:none; }
@selector: carousel;
.@{selector} {

@import to concatenate multiple files

While both Sass and Less can have a single compiled stylesheet made up of multiple @imported files, there are some differences. Sass partials start with an underscore character and never compile into their own stylesheet.

Less doesn’t use this underscore naming convention and any partial file can be compiled into it’s own file if told to. I started off using the Less.app Mac app to compile my code before moving over to a Grunt task. Unless you’re careful, the app will build every component file into it’s own stylesheet - which is probably not what you want!


One of the major differences between the two languages comes in the area of mixins. The basic syntax is as follows for each:

@mixin button($foreground, $background) {
.submit-button {
	@include button(#000, #fff);
.button(@foreground, @background) {
.submit-button {
	.button(#000, #fff);

I personally find the Less method here a bit confusing because without the @include keyword, you could be easy to mistake this for nesting selectors.

In Sass, the code for a mixin is never output until used with @include. In Less, mixins are output by default. This can be avoided by adding parentheses after the selector - even if the mixin doesn’t accept any arguments.

.brand-colors() {
.call-to-action {
// outputs
// .call-to-action { color:#000; background:#fff; }


extend is a bit like mixin but instead of outputting (and repeating) styles everywhere, common styles are comma separated in the compiled output.

.copy-font {
	font-family:'Baskerville', 'Palatino', 'Times', serif;
.sub-heading { @extend .copy-font; }

// output
//.sub-heading {
//	font-family:'Baskerville', 'Palatino', 'Times', serif;
//	text-transform:uppercase;
.copy-font {
	font-family:'Baskerville', 'Palatino', 'Times', serif;
.sub-heading { 

Sass has silent %placeholder classes that can be @extended as needed but not output in the compiled code. Less doesn’t have this feature but does do all kinds of weird and wonderful things with it’s version of the extend directive.

Custom Functions (sort of)

In Sass we have the @function declaration which allows an @return value to be passed back out of the function. In Less, something similar can be achieved with mixins.

@function calc-em($px-value, $context-px) {
	@return ($px-value/$context-px) * 1em
.headline {
	font-size: calc-em(10px, 16px);
// outputs 
//.headline { font-size:0.625em; }
.calc-em(@px-value, @context-px) {
	@font-size:(@px-value/@context-px) * 1em;
.headline {
	.calc-em(10px, 16px);

In the Less world, the @font-size variable created by the mixin is scoped within the .headline selector so can be used just like any normal variable.

Built in functions

Both pre-processors have an extensive reference of built-in functions:

These functions do things like lightening or darkening colours, checking variable types, rounding numbers up or down etc. Less has a vast array of built in math functions, some of which you’d have to use a library like Compass for in Sass.

Loops (recursive mixins in Less)

Sass has three different types of loops - I like them a lot! Less gets close with recursive mixins which are kind of like a for loop.

@for $i from 1 through 3 {
	.grid-#{$i} {
		width: $i * 300px;

// outputs
//.grid-1 { width:300px }
//.grid-2 { width:600px }
//.grid-3 { width:900px }
.generate-grid(@n, @i:1) when (@i =< @n) {
	.grid-@{i} {
		width: @i * 300px;
	.generate-grid(@n, (@i + 1));

Sass also has @while and @each loops which I use a lot - given how complex things get with Less recursive mixins, I’m not sure how practical it would be to try and replicate that kind of functionality - although if it can be done, I’d love to see it!

Wrap up

So, there you have it. A lot of similar functionality with a few differences in syntax and approach. As I’ve already mentioned, I’m a Sass fan and I’ll be sticking with it whenever I can - but that’s only because I’m used to it and find the syntax easier to read. The small amount of extra power of Sass goes slightly in it’s favour but if you’re already a Less power user, stick with what you know.

If you’re not pre-processing at all yet, hopefully this has given you an insight into the kind of things that can be done and a bit of a flavour of two of the more popular contenders.

I’d love to hear your thoughts, so shoot me a tweet and let me know your preference and why…!

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