diff --git a/.stylelintrc b/.stylelintrc
new file mode 100644
index 00000000..2c907302
--- /dev/null
+++ b/.stylelintrc
@@ -0,0 +1,3 @@
+{
+	"extends": "stylelint-config-wikimedia"
+}
diff --git a/Gruntfile.js b/Gruntfile.js
index 018adf8c..38a5102c 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -6,6 +6,7 @@ module.exports = function ( grunt ) {
 	grunt.loadNpmTasks( 'grunt-contrib-jshint' );
 	grunt.loadNpmTasks( 'grunt-jscs' );
 	grunt.loadNpmTasks( 'grunt-jsonlint' );
+	grunt.loadNpmTasks( 'grunt-stylelint' );
 
 	grunt.initConfig( {
 		jshint: {
@@ -23,6 +24,18 @@ module.exports = function ( grunt ) {
 		jscs: {
 			src: '<%= jshint.all %>'
 		},
+		stylelint: {
+			options: {
+				syntax: 'less'
+			},
+			src: [
+				'**/*.css',
+				'**/*.less',
+				'!lib/**',
+				'!node_modules/**',
+				'!vendor/**'
+			]
+		},
 		jsonlint: {
 			all: [
 				'**/*.json',
@@ -35,6 +48,6 @@ module.exports = function ( grunt ) {
 		}
 	} );
 
-	grunt.registerTask( 'test', [ 'jshint', 'jscs', 'jsonlint', 'banana' ] );
+	grunt.registerTask( 'test', [ 'jshint', 'jscs', 'stylelint', 'jsonlint', 'banana' ] );
 	grunt.registerTask( 'default', 'test' );
 };
diff --git a/package.json b/package.json
index 1805312b..b445d445 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,8 @@
     "grunt-banana-checker": "0.5.0",
     "grunt-contrib-jshint": "1.0.0",
     "grunt-jscs": "2.8.0",
-    "grunt-jsonlint": "1.0.7"
+    "grunt-jsonlint": "1.0.7",
+    "grunt-stylelint": "0.3.0",
+    "stylelint-config-wikimedia": "0.2.0"
   }
 }
diff --git a/resources/css/ext.uls-monobook.css b/resources/css/ext.uls-monobook.css
index 293b62b8..409c3e1b 100644
--- a/resources/css/ext.uls-monobook.css
+++ b/resources/css/ext.uls-monobook.css
@@ -1,3 +1,3 @@
-#pt-uls {
+#pt-uls { /* stylelint-disable selector-no-id */
 	text-transform: none;
 }
diff --git a/resources/css/ext.uls.compactlinks.less b/resources/css/ext.uls.compactlinks.less
index 0dbd7394..a3ba30f5 100644
--- a/resources/css/ext.uls.compactlinks.less
+++ b/resources/css/ext.uls.compactlinks.less
@@ -1,4 +1,6 @@
-@import "mediawiki.mixins";
+@import 'mediawiki.mixins';
+
+/* stylelint-disable selector-no-id */
 
 #p-lang .body ul .uls-trigger,
 #p-lang .pBody ul .uls-trigger {
@@ -6,12 +8,14 @@
 	padding: 0;
 }
 
+/* stylelint-enable selector-no-id */
+
 .mw-interlanguage-selector,
 .mw-interlanguage-selector:active {
 	cursor: pointer;
 	padding: 4px 6px 4px 25px;
 	font-size: 13px;
-	font-weight: 400;
+	font-weight: normal;
 	.background-image-svg( '../images/compact-links-trigger.svg', '../images/compact-links-trigger.png' );
 	background-size: 18px;
 	background-repeat: no-repeat;
@@ -22,16 +26,16 @@
 
 .mw-interlanguage-selector:active,
 .mw-interlanguage-selector.selector-open {
-	color: #555555;
-	background-color: #cccccc;
+	color: #555;
+	background-color: #ccc;
 }
 
 .interlanguage-uls-menu:before {
-	background: none repeat scroll 0 0 #FCFCFC;
+	background: none repeat scroll 0 0 #fcfcfc;
 	border-left: 1px solid rgba( 0, 0, 0, 0.2 );
 	border-top: 1px solid rgba( 0, 0, 0, 0.2 );
 	box-shadow: -2px -2px 2px rgba( 0, 0, 0, 0.1 );
-	content: "";
+	content: '';
 	height: 24px;
 	width: 24px;
 	left: -13px;
diff --git a/resources/css/ext.uls.css b/resources/css/ext.uls.css
index 5c359db1..faab31c1 100644
--- a/resources/css/ext.uls.css
+++ b/resources/css/ext.uls.css
@@ -21,7 +21,7 @@
 .uls-menu.callout .caret-before,
 .uls-menu.callout .caret-after {
 	border-top: 10px solid transparent;
-	border-right: 10px solid #C9C9C9;
+	border-right: 10px solid #c9c9c9;
 	border-bottom: 10px solid transparent;
 	display: inline-block;
 	left: -11px;
@@ -31,13 +31,13 @@
 }
 
 .uls-menu.callout .caret-after {
-	border-right: 10px solid #FCFCFC;
+	border-right: 10px solid #fcfcfc;
 	display: inline-block;
 	left: -10px;
 }
 
 .uls-menu.callout--languageselection .caret-after {
-	border-right: 10px solid #FFF;
+	border-right: 10px solid #fff;
 }
 
 .uls-ui-languages button {
@@ -58,7 +58,7 @@ button.uls-more-languages {
 }
 
 .settings-text {
-	color: #555555;
+	color: #555;
 	font-size: 9pt;
 }
 
@@ -74,10 +74,10 @@ div.display-settings-block:hover .settings-text {
 }
 
 .uls-icon-back {
-	background: transparent url('../images/back-grey-ltr.png') no-repeat scroll center center;
-	background-image: -webkit-linear-gradient(transparent, transparent), url('../images/back-grey-ltr.svg');
+	background: transparent url( ../images/back-grey-ltr.png ) no-repeat scroll center center;
+	background-image: -webkit-linear-gradient( transparent, transparent ), url( ../images/back-grey-ltr.svg );
 	/* @embed */
-	background-image: linear-gradient(transparent, transparent), url('../images/back-grey-ltr.svg');
+	background-image: linear-gradient( transparent, transparent ), url( ../images/back-grey-ltr.svg );
 	background-size: 28px;
 	background-position: center center;
 	height: 32px;
@@ -85,7 +85,7 @@ div.display-settings-block:hover .settings-text {
 	display: block;
 	position: absolute;
 	left: 0;
-	border-right: 1px solid #C9C9C9;
+	border-right: 1px solid #c9c9c9;
 	opacity: 0.8;
 }
 
@@ -96,7 +96,7 @@ div.display-settings-block:hover .settings-text {
 
 /* TODO: move to jquery.uls */
 .grid .uls-search {
-	padding-left: 0px;
+	padding-left: 0;
 }
 
 .uls-search-label {
@@ -105,5 +105,5 @@ div.display-settings-block:hover .settings-text {
 }
 
 .uls-filterinput {
-	padding-left: 0px;
+	padding-left: 0;
 }
diff --git a/resources/css/ext.uls.displaysettings.less b/resources/css/ext.uls.displaysettings.less
index d8204705..d488f3e9 100644
--- a/resources/css/ext.uls.displaysettings.less
+++ b/resources/css/ext.uls.displaysettings.less
@@ -1,4 +1,4 @@
-@import "mediawiki.mixins";
+@import 'mediawiki.mixins';
 
 div.display-settings-block {
 	background: transparent no-repeat left top;
@@ -22,7 +22,7 @@ div.display-settings-block {
 }
 
 .ext-uls-sub-panel {
-	border-top: 1px solid #EEEEEE;
+	border-top: 1px solid #eee;
 	padding-top: 25px;
 	top: -20px;
 	position: relative;
@@ -31,12 +31,12 @@ div.display-settings-block {
 
 .uls-display-settings-font-selectors {
 	margin: 5px 0 15px 0;
-	border-top: 1px solid #EEEEEE;
+	border-top: 1px solid #eee;
 }
 
 .uls-font-item {
-	border-bottom: 1px solid #EEEEEE;
-	background: #FBFBFB;
+	border-bottom: 1px solid #eee;
+	background: #fbfbfb;
 	margin: 0;
 	padding: 10px 0;
 }
@@ -48,7 +48,7 @@ div.display-settings-block {
 
 .uls-content-fonts:hover,
 .uls-ui-fonts:hover {
-	background-color: #F6F6F6;
+	background-color: #f6f6f6;
 }
 
 .uls-font-label strong {
@@ -56,7 +56,7 @@ div.display-settings-block {
 }
 
 .uls-font-label {
-	color: #555555;
+	color: #555;
 	font-size: 10pt;
 }
 
@@ -64,6 +64,6 @@ div.display-settings-block {
 	font-weight: bold;
 }
 
-#uls-display-settings-anon-log-in-cta {
+#uls-display-settings-anon-log-in-cta { /* stylelint-disable-line selector-no-id */
 	font-size: 10pt;
 }
diff --git a/resources/css/ext.uls.inputsettings.less b/resources/css/ext.uls.inputsettings.less
index 70f6b329..06e2f823 100644
--- a/resources/css/ext.uls.inputsettings.less
+++ b/resources/css/ext.uls.inputsettings.less
@@ -1,4 +1,4 @@
-@import "mediawiki.mixins";
+@import 'mediawiki.mixins';
 
 div.input-settings-block {
 	background: transparent no-repeat left top;
@@ -48,7 +48,7 @@ div.input-settings-block {
 	background: transparent no-repeat center top;
 	.background-image-svg( '../images/cog.svg', '../images/cog.png' );
 	background-size: auto 14px;
-	border-left: 1px solid #CCCCCC;
+	border-left: 1px solid #ccc;
 	width: 22px;
 	height: 14px;
 	position: absolute;
@@ -73,15 +73,15 @@ div.input-settings-block {
 	font-size: 11pt;
 }
 
-.down+.uls-input-settings-caret {
+.down + .uls-input-settings-caret {
 	display: inline-block;
 	width: 0;
 	height: 0;
-	border-top: none;
+	border-top: 0;
 	border-right: 8px solid transparent;
 	border-left: 8px solid transparent;
 	border-bottom: 8px solid #f0f0f0;
-	content: "";
+	content: '';
 	position: relative;
 	vertical-align: bottom;
 	top: 12px;
@@ -101,7 +101,7 @@ div.input-settings-block {
 }
 
 .uls-ime-notification-bubble .link {
-	color: #0645AD;
+	color: #0645ad;
 	cursor: pointer;
 }
 
diff --git a/resources/css/ext.uls.interlanguage.less b/resources/css/ext.uls.interlanguage.less
index c5617567..f1b76509 100644
--- a/resources/css/ext.uls.interlanguage.less
+++ b/resources/css/ext.uls.interlanguage.less
@@ -1,4 +1,6 @@
-@import "mediawiki.mixins";
+@import 'mediawiki.mixins';
+
+/* stylelint-disable selector-no-id */
 
 #p-lang .uls-settings-trigger {
 	background: transparent no-repeat right top;
diff --git a/resources/css/ext.uls.languagesettings.css b/resources/css/ext.uls.languagesettings.css
index 08ad3d36..f77cbbef 100644
--- a/resources/css/ext.uls.languagesettings.css
+++ b/resources/css/ext.uls.languagesettings.css
@@ -1,11 +1,13 @@
+/* stylelint-disable selector-no-id */
+
 #uls-settings-block {
-	border-top: 1px solid #C9C9C9;
+	border-top: 1px solid #c9c9c9;
 	background: #f8f8f8;
-	background: -webkit-gradient(linear, left top, left bottom, from(#FBFBFB), to(#F0F0F0));
-	background: -webkit-linear-gradient(top, #FBFBFB, #F0F0F0);
-	background: -moz-linear-gradient(top, #FBFBFB, #F0F0F0);
-	background: -o-linear-gradient(top, #FBFBFB, #F0F0F0);
-	background: linear-gradient(#FBFBFB, #F0F0F0);
+	background: -webkit-gradient( linear, left top, left bottom, from( #fbfbfb ), to( #f0f0f0 ) );
+	background: -webkit-linear-gradient( top, #fbfbfb, #f0f0f0 );
+	background: -moz-linear-gradient( top, #fbfbfb, #f0f0f0 );
+	background: -o-linear-gradient( top, #fbfbfb, #f0f0f0 );
+	background: linear-gradient( #fbfbfb, #f0f0f0 );
 	padding-left: 10px;
 	line-height: 1.2em;
 	border-radius: 0 0 5px 5px;
@@ -34,19 +36,15 @@
 	line-height: 20pt;
 	margin-top: 0;
 	font-weight: normal;
-	border: none;
+	border: 0;
 	padding: 15px 0 3px 15px;
 	color: #555;
 }
 
-.language-settings-buttons {
-	text-align: right;
-}
-
 #languagesettings-settings-panel {
 	padding-left: 5%;
 	color: #252525;
-	background: #FFFFFF;
+	background: #fff;
 	border-bottom-right-radius: 5px;
 }
 
@@ -73,18 +71,18 @@
 }
 
 #language-settings-dialog {
-	background: #FBFBFB;
+	background: #fbfbfb;
 }
 
 .uls-language-settings-close-block {
-	background: #FFFFFF;
+	background: #fff;
 }
 
 #languagesettings-panels .menu-section.active,
 #languagesettings-panels .menu-section.active:hover {
-	color: black;
-	background-color: #F0F0F0;
-	border-left-color: #3366BB;
+	color: #000;
+	background-color: #f0f0f0;
+	border-left-color: #36b;
 }
 
 .settings-menu-items .menu-section {
@@ -94,14 +92,15 @@
 }
 
 .settings-menu-items .menu-section:hover {
-	background-color: #F5F5F5;
+	background-color: #f5f5f5;
 }
 
 .language-settings-buttons {
-	border-top: 1px solid #F0F0F0;
+	border-top: 1px solid #f0f0f0;
 	margin-top: 25px;
 	padding: 15px;
 	width: auto;
+	text-align: right;
 }
 
 .language-settings-buttons button {
@@ -110,16 +109,16 @@
 
 .uls-ui-languages p,
 .checkbox {
-	color: #555555;
+	color: #555;
 	font-size: 10pt;
 }
 
 /* mediawiki.ui does not have a pressed state style. */
 #languagesettings-panels .mw-ui-pressed {
-	background-color: #D8D8D8;
+	background-color: #d8d8d8;
 }
 
-.checkbox input[type="checkbox"] {
+.checkbox input[type='checkbox'] {
 	margin-left: 0;
 }
 
@@ -127,7 +126,7 @@
 	color: #252525;
 }
 
-label.checkbox input[type="checkbox"] {
+label.checkbox input[type='checkbox'] {
 	float: left;
 }
 
@@ -136,10 +135,10 @@ label.checkbox input[type="checkbox"] {
 }
 
 .uls-icon-close {
-	background: transparent url('../images/close.png') no-repeat scroll center center;
-	background-image: -webkit-linear-gradient(transparent, transparent), url('../images/close.svg');
+	background: transparent url( ../images/close.png ) no-repeat scroll center center;
+	background-image: -webkit-linear-gradient( transparent, transparent ), url( ../images/close.svg );
 	/* @embed */
-	background-image: linear-gradient(transparent, transparent), url('../images/close.svg');
+	background-image: linear-gradient( transparent, transparent ), url( ../images/close.svg );
 	float: right;
 	padding: 15px;
 	cursor: pointer;
diff --git a/resources/css/ext.uls.nojs.css b/resources/css/ext.uls.nojs.css
index 99ec7e5d..10c965c2 100644
--- a/resources/css/ext.uls.nojs.css
+++ b/resources/css/ext.uls.nojs.css
@@ -1,4 +1,4 @@
 /* Don't show it to users who disabled JS */
-.client-nojs #pt-uls {
+.client-nojs #pt-uls { /* stylelint-disable-line selector-no-id */
 	display: none;
 }
diff --git a/resources/css/ext.uls.pt.less b/resources/css/ext.uls.pt.less
index 91d96ea7..821e31e3 100644
--- a/resources/css/ext.uls.pt.less
+++ b/resources/css/ext.uls.pt.less
@@ -1,4 +1,6 @@
-@import "mediawiki.mixins";
+@import 'mediawiki.mixins';
+
+/* stylelint-disable selector-no-id */
 
 /*
  * The trigger can be placed in the personal toolbar near the username
@@ -24,19 +26,20 @@
 /* Opera for some inexplicable reason confuses right and left padding with */
 /* RTL text direction here (bug T47142). x:-o-prefocus won't match anything, */
 /* but will make other browsers ignore this rule. */
-x:-o-prefocus, body.rtl li#pt-uls {
+x:-o-prefocus,
+body.rtl li#pt-uls {
 	/* @noflip */
 	direction: ltr;
 }
 
 #uls-settings-block {
-	border-top: 1px solid #C9C9C9;
+	border-top: 1px solid #c9c9c9;
 	background: #f8f8f8;
-	background: -webkit-gradient(linear, left top, left bottom, from(#FBFBFB), to(#F0F0F0));
-	background: -webkit-linear-gradient(top, #FBFBFB, #F0F0F0);
-	background: -moz-linear-gradient(top, #FBFBFB, #F0F0F0);
-	background: -o-linear-gradient(top, #FBFBFB, #F0F0F0);
-	background: linear-gradient(#FBFBFB, #F0F0F0);
+	background: -webkit-gradient( linear, left top, left bottom, from( #fbfbfb ), to( #f0f0f0 ) );
+	background: -webkit-linear-gradient( top, #fbfbfb, #f0f0f0 );
+	background: -moz-linear-gradient( top, #fbfbfb, #f0f0f0 );
+	background: -o-linear-gradient( top, #fbfbfb, #f0f0f0 );
+	background: linear-gradient( #fbfbfb, #f0f0f0 );
 	padding-left: 10px;
 	line-height: 1.2em;
 	border-radius: 0 0 5px 5px;