diff --git a/custom_metrics/sass.js b/custom_metrics/sass.js
new file mode 100644
index 00000000..6781a44b
--- /dev/null
+++ b/custom_metrics/sass.js
@@ -0,0 +1,297 @@
+//[sass]
+const SassFunctions = [
+	// Color
+	"color.adjust", "adjust-color",
+	"color.scale", "scale-color",
+	"color.change",
+	"adjust-hue",
+	"opacity",
+	"darken", "lighten",
+	"desaturate", "saturate",
+	"opacify", "transparentize",
+	"fade-in", "fade-out",
+
+	...[
+		"red", "green", "blue",
+		"hue", "saturation", "lightness",
+		"alpha", "complement",
+		"grayscale",
+		"ie-hex-str",
+		"invert",
+		"mix"
+	].flatMap(n => ["color." + n, n]),
+
+	// List
+	"list.separator", "list-separator",
+
+	...[
+		"append", "index", "is-bracketed", "join",
+	 "length", "set-nth", "nth", "zip"
+	].flatMap(n => ["list." + n, n]),
+
+	// Map
+	...[
+		"get", "has-key", "keys", "merge", "remove", "values"
+	].flatMap(n => ["map." + n, "map-" + n]),
+
+	// Math
+	...[
+		"ceil", "floor", "round",
+		"clamp", "min", "max",
+		"abs", "comparable", "unit", "percentage", "random"
+	].flatMap(n => ["math." + n, n]),
+	"math.hypot", "math.log", "math.pow", "math.sqrt",
+	"math.sin", "math.cos", "math.tan",
+	"math.asin", "math.acos", "math.atan", "math.atan2",
+	"math.is-unitless", "unitless",
+
+	// Meta
+	"meta.load-css",
+	"meta.module-functions", "meta.module-variables",
+	...[
+		"call", "get-function", "keywords",
+		"content-exists", "feature-exists", "function-exists", "global-variable-exists", "variable-exists", "mixin-exists",
+		"inspect", "type-of"
+	].flatMap(n => ["meta." + n, n]),
+
+	"if"
+];
+
+const sortObject = (obj, f = x => x) => Object.fromEntries(Object.entries(obj).sort((a, b) => f(b[1]) - f(a[1])));
+
+function analyzeSCSS(scss, ret) {
+	if (!scss) {
+		return null;
+	}
+
+	// Drop (most) comments to minimize false positives since we have to parse with regexes
+	// We want to be conservative here and err on the side of NOT removing comments
+	scss = scss.replace(/^\s*\/\*[\s\S]*?\*\//mg, "");
+	scss = scss.replace(/^\s*\/\/.+/mg, "");
+
+	// Most popular variable names
+	ret.variables = {};
+	scss.replace(/\$[\w-]+\b/g, variable => {
+		ret.variables[variable] = (ret.variables[variable] || 0) + 1;
+	});
+	ret.variables = sortObject(ret.variables);
+
+	// Mixins
+	// Note: We are not taking the Indented Mixin Syntax into account
+	ret.mixins = {};
+	scss.replace(/@mixin\s+([\w-]+)(?:\((.+?)\))?/g, ($0, name, args) => {
+		// Note: - and _ are equivalent in mixin names and refer to the same mixin
+		//         we are not taking that into account here. This applies to functions too (below)
+		ret.mixins[name] = {
+			// Default values can't have commas, so split should work
+			args: args?.split(/\s*,\s*/), // TODO separate name from default value?
+			calls: scss.match(RegExp("@include\\s+" + name + "\\b", "gi"))?.length
+		};
+	});
+	ret.mixins = sortObject(ret.mixins, o => o.calls);
+
+	// Custom functions
+	ret.functions = {};
+	let lastName; // used to track down the nearest @return after a @function
+	scss.replace(/@function\s+([\w-]+)(?:\((.+?)\))?|@return (.+)/g, ($0, name, args, returnValue) => {
+		if ($0.indexOf("@return") === 0 && lastName) {
+			ret.functions[lastName].returns = ret.functions[lastName].returns || [];
+			ret.functions[lastName].returns.push(returnValue);
+			return $0;
+		}
+
+		lastName = name;
+		ret.functions[name] = {
+			// Default values can't have commas, so split should work
+			args: args?.split(/\s*,\s*/), // TODO separate name from default value?
+			calls: scss.match(RegExp("\\b" + name + "\\(", "gi"))?.length
+		};
+	});
+	ret.functions = sortObject(ret.functions, o => o.calls);
+
+	// TODO Measure usage of Sass functions
+	ret.functionCalls = {};
+	let functionCallRegex = new RegExp(`(?<![-.\\w])(${SassFunctions.join("|").replace(".", "\\.")})\\(`, "gi");
+	scss.replace(functionCallRegex, ($0, name) => {
+		ret.functionCalls[name] = (ret.functionCalls[name] || 0) + 1;
+	});
+	ret.functionCalls = sortObject(ret.functionCalls);
+
+	// Conditionals
+	ret.ifs = [];
+	scss.replace(/@(?:(else )?if\s+?(.+?)|@else)(?=\s*\{)/g, ($0, elseIf, test) => {
+		if ($0 === "@else") {
+			// Else for previous condition
+			let obj = ret.ifs.pop();
+			console.log(ret.ifs, obj);
+			obj.hasElse = true;
+			ret.ifs.push(obj);
+		}
+		else if (elseIf) {
+			// Else if for previous condition
+			let obj = ret.ifs.pop();
+			obj.elseIfs = obj.elseIfs || [];
+			obj.elseIfs.push(test);
+			ret.ifs.push(obj);
+		}
+		else {
+			// New conditional
+			ret.ifs.push({test});
+		}
+	});
+
+	// @each, @for, @while Loops
+	ret.eaches = {};
+	scss.replace(/@each\s+(.+ in .+)(?=\s*\{)/g, ($0, args) => {
+		ret.eaches[args] = (ret.eaches[args] || 0) + 1;
+	});
+
+	ret.fors = {};
+	// console.log("@for", scss);
+	scss.replace(/@for\s+(.+)(?=\s*\{)/g, ($0, args) => {
+		ret.fors[args] = (ret.fors[args] || 0) + 1;
+	});
+
+	ret.whiles = {};
+	scss.replace(/@while\s+(.+)(?=\s*\{)/g, ($0, args) => {
+		ret.whiles[args] = (ret.whiles[args] || 0) + 1;
+	});
+
+	// @extend
+	ret.extends = {};
+	scss.replace(/@extend\s*(.+)(?=\s*(?:[;}]|$))/g, ($0, selector) => {
+		ret.extends[selector] = (ret.extends[selector] || 0) + 1;
+	});
+
+	// @error
+	ret.errors = scss.match(/@error (.+)/g)?.map(e => e.slice(7));
+
+	// CSS variables that are set with Sass variables
+	// Note that this will fail on multiline values (it will return the first line only)
+	ret.variablesCombined = {value: {}, name: {}};
+	scss.replace(/(?<=^|\s)--([\w-]+):\s*(.*#\{.+\}.*)\s*$/gm, ($0, name, value) => {
+		ret.variablesCombined.value["--" + name] = value;
+	});
+	scss.replace(/(?<=^|\s)--([\w-]*#\{.+?\}[\w-]*):\s*(.+?)(?=;|$)/gm, ($0, name, value) => {
+		ret.variablesCombined.name["--" + name] = value;
+	});
+
+	// Heuristic for nesting &
+	ret.nested = {
+		"descendant": scss.match(/&\s+(?=[\w[.:#])/g)?.length,
+		">": scss.match(/&\s*(?=>)/g)?.length,
+		"+": scss.match(/&\s*(?=\+)/g)?.length,
+		"~": scss.match(/&\s*(?=~)/g)?.length,
+		"lone": scss.match(/&\s*(?=[,{]|$})/g)?.length,
+		"pseudo-element": scss.match(/&::/g)?.length,
+		"pseudo-class": scss.match(/&:(?!:)/g)?.length,
+		"id": scss.match(/&#\w+/g)?.length,
+		"class": scss.match(/&\.\w+/g)?.length,
+		"attr": scss.match(/&\[\w+/g)?.length,
+	};
+}
+
+let results = (async () => {
+
+const results = {};
+const $$ = s => [...document.querySelectorAll(s)];
+const sourcemapRegex = /\/\*[#@] sourceMappingURL=(.+?) \*\//;
+
+let stylesheets = $WPT_BODIES.filter(request => request.type == "Stylesheet")
+	.map(file => {
+		return {url: file.url, body: file.response_body};
+	});
+
+results.stylesheets = {
+	remote: stylesheets.length
+};
+
+stylesheets.push(...$$("style").map(s => {
+	return {
+		url: location,
+		body: s.textContent
+	}
+}));
+
+results.stylesheets.inline = stylesheets.length - results.stylesheets.remote;
+
+let sourcemapURLs = stylesheets.map(o => {
+	if (o) {
+		let url = o.body.match(sourcemapRegex)?.[1];
+
+		if (url) {
+			// Source map URL is relative to stylesheet URL
+			return new URL(url, o.url);
+		}
+	}
+}).filter(url => !!url);
+
+results.sourcemaps = {
+	count: sourcemapURLs.length,
+	ext: {}
+};
+
+if (sourcemapURLs.length === 0) {
+	return results;
+}
+
+// Assumption: Either all sources are SCSS or none.
+let scss = await Promise.all(sourcemapURLs.map(async url => {
+	try {
+		var response = await fetch(url);
+		var json = await response.json();
+	}
+	catch (e) {
+		return;
+	}
+
+	let sources = json.sources;
+	let base = json.sourceRoot? new URL(json.sourceRoot, url) : url;
+	let scss = 0;
+
+	sources = sources.map(s => {
+		let url = new URL(s, base);
+		let ext = url.pathname.match(/\.(\w+)$/)?.[1];
+
+		if (ext) {
+			results.sourcemaps.ext[ext] = (results.sourcemaps.ext[ext] || 0) + 1;
+
+			if (ext === "scss") {
+				scss++;
+			}
+		}
+
+		return url;
+	});
+
+	if (scss > 0) {
+		if (json.sourcesContent) {
+			// Source is already here, no more requests needed, yay!
+			return json.sourcesContent;
+		}
+
+		let code = await Promise.all(sources.map(async s => {
+			let response = await fetch(s);
+			let text = response.ok? await response.text() : "";
+			return text;
+		}));
+
+		return code.join("\n");
+	}
+}));
+
+scss = scss.filter(s => !!s).join("\n");
+
+results.scss = {
+	size: scss.length,
+	stats: {}
+};
+
+analyzeSCSS(scss, results.scss.stats)
+
+return results;
+
+})();
+
+// results.then(r => console.log(JSON.stringify(r, null, "\t")));
+return results.then(r => JSON.stringify(r));