diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..349e87e
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,183 @@
+export interface Options {
+	/**
+	 * @default 'http:'
+	 */
+	defaultProtocol?: string;
+
+	/**
+	 * Prepends `defaultProtocol` to the URL if it's protocol-relative.
+	 *
+	 * @default true
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('//sindresorhus.com:80/');
+	 * //=> 'http://sindresorhus.com'
+	 *
+	 * normalizeUrl('//sindresorhus.com:80/', {normalizeProtocol: false});
+	 * //=> '//sindresorhus.com'
+	 */
+	normalizeProtocol?: boolean;
+
+	/**
+	 * Normalizes `https:` URLs to `http:`.
+	 *
+	 * @default false
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('https://sindresorhus.com:80/');
+	 * //=> 'https://sindresorhus.com'
+	 *
+	 * normalizeUrl('https://sindresorhus.com:80/', {forceHttp: true});
+	 * //=> 'http://sindresorhus.com'
+	 */
+	forceHttp?: boolean;
+
+	/**
+	 * Normalizes `http:` URLs to `https:`.
+	 *
+	 * This option can't be used with the `forceHttp` option at the same time.
+	 *
+	 * @default false
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('https://sindresorhus.com:80/');
+	 * //=> 'https://sindresorhus.com'
+	 *
+	 * normalizeUrl('http://sindresorhus.com:80/', {forceHttps: true});
+	 * //=> 'https://sindresorhus.com'
+	 */
+	forceHttps?: boolean;
+
+	/**
+	 * Strip the [authentication](https://en.wikipedia.org/wiki/Basic_access_authentication) part of a URL.
+	 *
+	 * @default true
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('user:password@sindresorhus.com');
+	 * //=> 'https://sindresorhus.com'
+	 *
+	 * normalizeUrl('user:password@sindresorhus.com', {stripAuthentication: false});
+	 * //=> 'https://user:password@sindresorhus.com'
+	 */
+	stripAuthentication?: boolean;
+
+	/**
+	 * Removes hash from the URL.
+	 *
+	 * @default false
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('sindresorhus.com/about.html#contact');
+	 * //=> 'http://sindresorhus.com/about.html#contact'
+	 *
+	 * normalizeUrl('sindresorhus.com/about.html#contact', {stripHash: true});
+	 * //=> 'http://sindresorhus.com/about.html'
+	 */
+	stripHash?: boolean;
+
+	/**
+	 * Removes HTTP(S) protocol from an URL `http://sindresorhus.com` → `sindresorhus.com`.
+	 *
+	 * @default false
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('https://sindresorhus.com');
+	 * //=> 'https://sindresorhus.com'
+	 *
+	 * normalizeUrl('sindresorhus.com', {stripProtocol: true});
+	 * //=> 'sindresorhus.com'
+	 */
+	stripProtocol?: boolean;
+
+	/**
+	 * Removes `www.` from the URL.
+	 *
+	 * @default true
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('http://www.sindresorhus.com');
+	 * //=> 'http://sindresorhus.com'
+	 *
+	 * normalizeUrl('http://www.sindresorhus.com', {stripWWW: false});
+	 * //=> 'http://www.sindresorhus.com'
+	 */
+	stripWWW?: boolean;
+
+	/**
+	 * Removes query parameters that matches any of the provided strings or regexes.
+	 *
+	 * @default [/^utm_\w+/i]
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('www.sindresorhus.com?foo=bar&ref=test_ref', {
+	 *     removeQueryParameters: ['ref']
+	 * });
+	 * //=> 'http://sindresorhus.com/?foo=bar'
+	 */
+	removeQueryParameters?: (RegExp | string)[];
+
+	/**
+	 * Removes trailing slash.
+	 *
+	 * **Note**: Trailing slash is always removed if the URL doesn't have a pathname.
+	 *
+	 * @default true
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('http://sindresorhus.com/redirect/');
+	 * //=> 'http://sindresorhus.com/redirect'
+	 *
+	 * normalizeUrl('http://sindresorhus.com/redirect/', {removeTrailingSlash: false});
+	 * //=> 'http://sindresorhus.com/redirect/'
+	 *
+	 * normalizeUrl('http://sindresorhus.com/', {removeTrailingSlash: false});
+	 * //=> 'http://sindresorhus.com'
+	 */
+	removeTrailingSlash?: boolean;
+
+	/**
+	 * Removes the default directory index file from path that matches any of the provided strings or regexes.
+	 * When `true`, the regex `/^index\.[a-z]+$/` is used.
+	 *
+	 * @default false
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('www.sindresorhus.com/foo/default.php', {
+	 *     removeDirectoryIndex: [/^default\.[a-z]+$/]
+	 * });
+	 * //=> 'http://sindresorhus.com/foo'
+	 */
+	removeDirectoryIndex?: (RegExp | string)[];
+
+	/**
+	 * Sorts the query parameters alphabetically by key.
+	 *
+	 * @default true
+	 *
+	 * @example
+	 *
+	 * normalizeUrl('www.sindresorhus.com?b=two&a=one&c=three', {
+	 *     sortQueryParameters: false
+	 * });
+	 * //=> 'http://sindresorhus.com/?b=two&a=one&c=three'
+	 */
+	sortQueryParameters?: boolean;
+}
+
+/**
+ * [Normalize](https://en.wikipedia.org/wiki/URL_normalization) a URL.
+ *
+ * @param url - URL to normalize.
+ */
+export default function normalizeUrl(url: string, options?: Options): string;
diff --git a/index.js b/index.js
index f0c868b..d11ffb3 100644
--- a/index.js
+++ b/index.js
@@ -6,7 +6,7 @@ const testParameter = (name, filters) => {
 	return filters.some(filter => filter instanceof RegExp ? filter.test(name) : filter === name);
 };
 
-module.exports = (urlString, options) => {
+const normalizeUrl = (urlString, options) => {
 	options = {
 		defaultProtocol: 'http:',
 		normalizeProtocol: true,
@@ -78,6 +78,7 @@ module.exports = (urlString, options) => {
 			if (/^(?!\/)/g.test(p1)) {
 				return `${p1}/`;
 			}
+
 			return '/';
 		});
 	}
@@ -153,3 +154,6 @@ module.exports = (urlString, options) => {
 
 	return urlString;
 };
+
+module.exports = normalizeUrl;
+module.exports.default = normalizeUrl;
diff --git a/index.test-d.ts b/index.test-d.ts
new file mode 100644
index 0000000..dad80be
--- /dev/null
+++ b/index.test-d.ts
@@ -0,0 +1,24 @@
+import {expectType} from 'tsd-check';
+import normalizeUrl from '.';
+
+expectType<string>(normalizeUrl('sindresorhus.com'));
+expectType<string>(normalizeUrl('HTTP://xn--xample-hva.com:80/?b=bar&a=foo'));
+
+normalizeUrl('//sindresorhus.com:80/', {defaultProtocol: 'https:'});
+normalizeUrl('//sindresorhus.com:80/', {normalizeProtocol: false});
+normalizeUrl('https://sindresorhus.com:80/', {forceHttp: true});
+normalizeUrl('http://sindresorhus.com:80/', {forceHttps: true});
+normalizeUrl('user:password@sindresorhus.com', {stripAuthentication: false});
+normalizeUrl('sindresorhus.com/about.html#contact', {stripHash: true});
+normalizeUrl('https://sindresorhus.com', {stripProtocol: true});
+normalizeUrl('http://www.sindresorhus.com', {stripWWW: false});
+normalizeUrl('www.sindresorhus.com?foo=bar&ref=test_ref', {
+	removeQueryParameters: ['ref', /test/]
+});
+normalizeUrl('http://sindresorhus.com/', {removeTrailingSlash: false});
+normalizeUrl('www.sindresorhus.com/foo/default.php', {
+	removeDirectoryIndex: [/^default\.[a-z]+$/, 'foo']
+});
+normalizeUrl('www.sindresorhus.com?b=two&a=one&c=three', {
+	sortQueryParameters: false
+});
diff --git a/package.json b/package.json
index c952f02..1770c77 100644
--- a/package.json
+++ b/package.json
@@ -13,10 +13,11 @@
 		"node": ">=8"
 	},
 	"scripts": {
-		"test": "xo && nyc ava"
+		"test": "xo && nyc ava && tsd-check"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"normalize",
@@ -34,9 +35,10 @@
 		"canonical"
 	],
 	"devDependencies": {
-		"ava": "^0.25.0",
+		"ava": "^1.2.1",
 		"coveralls": "^3.0.0",
 		"nyc": "^13.1.0",
-		"xo": "^0.23.0"
+		"tsd-check": "^0.3.0",
+		"xo": "^0.24.0"
 	}
 }