diff --git a/.gitignore b/.gitignore
index 25871d043..d6cdfd5a0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 node_modules
 build/
+composer.lock
diff --git a/pwa-wp.php b/pwa-wp.php
index 90cf5bcd8..39e53b247 100644
--- a/pwa-wp.php
+++ b/pwa-wp.php
@@ -26,22 +26,22 @@
 define( 'PWAWP_PLUGIN_FILE', __FILE__ );
 define( 'PWAWP_PLUGIN_DIR', dirname( __FILE__ ) );
 
-pwawp_init();
+/** WP_Web_App_Manifest Class */
+require PWAWP_PLUGIN_DIR . '/wp-includes/class-wp-web-app-manifest.php';
 
-/**
- * Loads and instantiates the classes.
- */
-function pwawp_init() {
-	$classes = array(
-		'web-app-manifest',
-		'https-detection',
-	);
-	foreach ( $classes as $class ) {
-		require PWAWP_PLUGIN_DIR . "/php/class-wp-{$class}.php";
-	}
+/** WP_HTTPS_Detection Class */
+require PWAWP_PLUGIN_DIR . '/wp-includes/class-wp-https-detection.php';
+
+/** WP_Service_Workers Class */
+require PWAWP_PLUGIN_DIR . '/wp-includes/class-wp-service-workers.php';
+
+/** WordPress Service Worker Functions */
+require PWAWP_PLUGIN_DIR . '/wp-includes/service-workers.php';
+
+/** Amend default filters */
+require PWAWP_PLUGIN_DIR . '/wp-includes/default-filters.php';
 
-	$wp_web_app_manifest = new WP_Web_App_Manifest();
-	$wp_web_app_manifest->init();
-	$wp_https_detection = new WP_HTTPS_Detection();
-	$wp_https_detection->init();
-}
+$wp_web_app_manifest = new WP_Web_App_Manifest();
+$wp_web_app_manifest->init();
+$wp_https_detection = new WP_HTTPS_Detection();
+$wp_https_detection->init();
diff --git a/tests/test-class-wp-service-workers.php b/tests/test-class-wp-service-workers.php
new file mode 100644
index 000000000..7ac591ae6
--- /dev/null
+++ b/tests/test-class-wp-service-workers.php
@@ -0,0 +1,59 @@
+<?php
+/**
+ * Tests for class WP_Service_Workers.
+ *
+ * @package PWA
+ */
+
+/**
+ * Tests for class WP_Web_App_Manifest.
+ */
+class Test_WP_Service_Workers extends WP_UnitTestCase {
+
+	/**
+	 * Tested instance.
+	 *
+	 * @var WP_Service_Workers
+	 */
+	public $instance;
+
+	/**
+	 * Setup.
+	 *
+	 * @inheritdoc
+	 */
+	public function setUp() {
+		parent::setUp();
+		$this->instance = new WP_Service_Workers();
+	}
+
+	/**
+	 * Test class constructor.
+	 *
+	 * @covers WP_Service_Workers::__construct()
+	 */
+	public function test_construct() {
+		$service_workers = new WP_Service_Workers();
+		$this->assertEquals( 'WP_Service_Workers', get_class( $service_workers ) );
+	}
+
+	/**
+	 * Test adding new service worker.
+	 *
+	 * @covers WP_Service_Workers::add()
+	 */
+	public function test_register() {
+		$this->instance->register( 'foo', '/test-sw.js', array( 'bar' ) );
+
+		$default_scope = site_url( '/', 'relative' );
+
+		$this->assertTrue( in_array( $default_scope, $this->instance->get_scopes(), true ) );
+		$this->assertTrue( isset( $this->instance->registered['foo'] ) );
+
+		$registered_sw = $this->instance->registered['foo'];
+
+		$this->assertEquals( '/test-sw.js', $registered_sw->src );
+		$this->assertTrue( in_array( $default_scope, $registered_sw->args['scopes'], true ) );
+		$this->assertEquals( array( 'bar' ), $registered_sw->deps );
+	}
+}
diff --git a/php/class-wp-https-detection.php b/wp-includes/class-wp-https-detection.php
similarity index 100%
rename from php/class-wp-https-detection.php
rename to wp-includes/class-wp-https-detection.php
diff --git a/wp-includes/class-wp-service-workers.php b/wp-includes/class-wp-service-workers.php
new file mode 100644
index 000000000..72eb5580f
--- /dev/null
+++ b/wp-includes/class-wp-service-workers.php
@@ -0,0 +1,205 @@
+<?php
+/**
+ * Dependencies API: WP_Service_Workers class
+ *
+ * @since ?
+ *
+ * @package PWA
+ */
+
+/**
+ * Class used to register service workers.
+ *
+ * @since ?
+ *
+ * @see WP_Dependencies
+ */
+class WP_Service_Workers extends WP_Scripts {
+
+	/**
+	 * Param for service workers.
+	 *
+	 * @var string
+	 */
+	public $query_var = 'wp_service_worker';
+
+	/**
+	 * Output for service worker scope script.
+	 *
+	 * @var string
+	 */
+	public $output = '';
+
+	/**
+	 * Initialize the class.
+	 */
+	public function init() {
+		/**
+		 * Fires when the WP_Service_Workers instance is initialized.
+		 *
+		 * @param WP_Service_Workers $this WP_Service_Workers instance (passed by reference).
+		 */
+		do_action_ref_array( 'wp_default_service_workers', array( &$this ) );
+	}
+
+	/**
+	 * Register service worker.
+	 *
+	 * Registers service worker if no item of that name already exists.
+	 *
+	 * @param string          $handle Name of the item. Should be unique.
+	 * @param string|callable $src    URL to the source in the WordPress install, or a callback that returns the JS to include in the service worker.
+	 * @param array           $deps   Optional. An array of registered item handles this item depends on. Default empty array.
+	 * @param array           $scopes Optional. Scopes of the service worker. Default relative path.
+	 * @return bool Whether the item has been registered. True on success, false on failure.
+	 */
+	public function register( $handle, $src, $deps = array(), $scopes = array() ) {
+
+		// Set default scope if missing.
+		if ( empty( $scopes ) ) {
+			$scopes = array( site_url( '/', 'relative' ) );
+		}
+		return parent::add( $handle, $src, $deps, false, compact( 'scopes' ) );
+	}
+
+	/**
+	 * Get service worker logic for scope.
+	 *
+	 * @param string $scope Scope of the Service Worker.
+	 */
+	public function serve_request( $scope ) {
+
+		header( 'Content-Type: text/javascript; charset=utf-8' );
+		nocache_headers();
+
+		if ( ! in_array( $scope, $this->get_scopes(), true ) ) {
+			status_header( 404 );
+			return;
+		}
+
+		$scope_items = array();
+
+		// Get handles from the relevant scope only.
+		foreach ( $this->registered as $handle => $item ) {
+			if ( in_array( $scope, $item->args['scopes'], true ) ) {
+				$scope_items[] = $handle;
+			}
+		}
+
+		$this->output = '';
+		$this->do_items( $scope_items );
+
+		$file_hash = md5( $this->output );
+		header( "Etag: $file_hash" );
+
+		$etag_header = isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ? trim( $_SERVER['HTTP_IF_NONE_MATCH'] ) : false;
+		if ( $file_hash === $etag_header ) {
+			status_header( 304 );
+			return;
+		}
+
+		echo $this->output; // phpcs:ignore WordPress.XSS.EscapeOutput, WordPress.Security.EscapeOutput
+	}
+
+	/**
+	 * Get all scopes.
+	 *
+	 * @return array Array of scopes.
+	 */
+	public function get_scopes() {
+
+		$scopes = array();
+		foreach ( $this->registered as $handle => $item ) {
+			$scopes = array_merge( $scopes, $item->args['scopes'] );
+		}
+		return array_unique( $scopes );
+	}
+
+	/**
+	 * Process one registered script.
+	 *
+	 * @param string $handle Handle.
+	 * @param bool   $group Group.
+	 * @return void
+	 */
+	public function do_item( $handle, $group = false ) {
+
+		$obj = $this->registered[ $handle ];
+
+		if ( is_callable( $obj->src ) ) {
+			$this->output .= call_user_func( $obj->src ) . "\n";
+		} else {
+			$validated_path = $this->get_validated_file_path( $obj->src );
+			if ( is_wp_error( $validated_path ) ) {
+				_doing_it_wrong(
+					__FUNCTION__,
+					/* translators: %s is file URL */
+					sprintf( esc_html__( 'Service worker src is incorrect: %s', 'pwa' ), esc_html( $obj->src ) ),
+					'0.1'
+				);
+
+				/* translators: %s is file URL */
+				$this->output .= "console.warn( '" . sprintf( esc_html__( 'Service worker src is incorrect: %s', 'pwa' ), esc_html( $obj->src ) ) . "' );\n";
+			} else {
+				/* translators: %s is file URL */
+				$this->output .= sprintf( esc_html( "\n/* Source: %s */\n" ), esc_url( $obj->src ) );
+
+				$this->output .= @file_get_contents( $this->get_validated_file_path( $obj->src ) ) . "\n"; // phpcs:ignore Generic.PHP.NoSilencedErrors.Discouraged, WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents, WordPress.WP.AlternativeFunctions.file_system_read_file_get_contents
+			}
+		}
+	}
+
+	/**
+	 * Remove URL scheme.
+	 *
+	 * @param string $schemed_url URL.
+	 * @return string URL.
+	 */
+	public function remove_url_scheme( $schemed_url ) {
+		return preg_replace( '#^\w+:(?=//)#', '', $schemed_url );
+	}
+
+	/**
+	 * Get validated path to file.
+	 *
+	 * @param string $url Relative path.
+	 * @return null|string|WP_Error
+	 */
+	public function get_validated_file_path( $url ) {
+		if ( ! is_string( $url ) ) {
+			return new WP_Error( 'incorrect_path_format', esc_html__( 'URL has to be a string', 'pwa' ) );
+		}
+
+		$needs_base_url = ! preg_match( '|^(https?:)?//|', $url );
+		$base_url       = site_url();
+
+		if ( $needs_base_url ) {
+			$url = $base_url . $url;
+		}
+
+		// Strip URL scheme, query, and fragment.
+		$url = $this->remove_url_scheme( preg_replace( ':[\?#].*$:', '', $url ) );
+
+		$content_url  = $this->remove_url_scheme( content_url( '/' ) );
+		$allowed_host = wp_parse_url( $content_url, PHP_URL_HOST );
+
+		$url_host = wp_parse_url( $url, PHP_URL_HOST );
+
+		if ( $allowed_host !== $url_host ) {
+			/* translators: %s is file URL */
+			return new WP_Error( 'external_file_url', sprintf( __( 'URL is located on an external domain: %s.', 'pwa' ), $url_host ) );
+		}
+
+		$file_path = null;
+		if ( 0 === strpos( $url, $content_url ) ) {
+			$file_path = WP_CONTENT_DIR . substr( $url, strlen( $content_url ) - 1 );
+		}
+
+		if ( ! $file_path || false !== strpos( '../', $file_path ) || 0 !== validate_file( $file_path ) || ! file_exists( $file_path ) ) {
+			/* translators: %s is file URL */
+			return new WP_Error( 'file_path_not_found', sprintf( __( 'Unable to locate filesystem path for %s.', 'pwa' ), $url ) );
+		}
+
+		return $file_path;
+	}
+}
diff --git a/php/class-wp-web-app-manifest.php b/wp-includes/class-wp-web-app-manifest.php
similarity index 100%
rename from php/class-wp-web-app-manifest.php
rename to wp-includes/class-wp-web-app-manifest.php
diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
new file mode 100644
index 000000000..18417d143
--- /dev/null
+++ b/wp-includes/default-filters.php
@@ -0,0 +1,14 @@
+<?php
+/**
+ * Sets up the default filters and actions for PWA hooks.
+ *
+ * @package PWA
+ */
+
+foreach ( array( 'wp_print_scripts', 'admin_print_scripts', 'customize_controls_print_scripts' ) as $filter ) {
+	add_filter( $filter, 'wp_print_service_workers', 9 );
+}
+
+add_action( 'parse_request', 'wp_service_worker_loaded' );
+
+add_filter( 'query_vars', 'wp_add_service_worker_query_var' );
diff --git a/wp-includes/service-workers.php b/wp-includes/service-workers.php
new file mode 100644
index 000000000..bb6be7a59
--- /dev/null
+++ b/wp-includes/service-workers.php
@@ -0,0 +1,106 @@
+<?php
+/**
+ * Service Worker functions.
+ *
+ * @since ?
+ *
+ * @package PWA
+ */
+
+/**
+ * Initialize $wp_service_workers if it has not been set.
+ *
+ * @global WP_Service_Workers $wp_service_workers
+ * @return WP_Service_Workers WP_Service_Workers instance.
+ */
+function wp_service_workers() {
+	global $wp_service_workers;
+	if ( ! ( $wp_service_workers instanceof WP_Service_Workers ) ) {
+		$wp_service_workers = new WP_Service_Workers();
+	}
+	return $wp_service_workers;
+}
+
+/**
+ * Register a new service worker.
+ *
+ * @since ?
+ *
+ * @param string          $handle Name of the service worker. Should be unique.
+ * @param string|callable $src    Callback method or relative path of the service worker.
+ * @param array           $deps   Optional. An array of registered script handles this depends on. Default empty array.
+ * @param array           $scopes Optional Scopes of the service worker.
+ * @return bool Whether the script has been registered. True on success, false on failure.
+ */
+function wp_register_service_worker( $handle, $src, $deps = array(), $scopes = array() ) {
+	$service_workers = wp_service_workers();
+	$registered      = $service_workers->register( $handle, $src, $deps, $scopes );
+
+	return $registered;
+}
+
+/**
+ * Get service worker URL by scope.
+ *
+ * @todo Use home_url() instead? See get_rest_url().
+ *
+ * @param string $scope Scope, for example 'wp-admin'. Defaults to '/'.
+ * @return string Service Worker URL.
+ */
+function wp_get_service_worker_url( $scope = null ) {
+
+	if ( ! $scope ) {
+		$scope = site_url( '/', 'relative' );
+	}
+
+	return add_query_arg(
+		array( 'wp_service_worker' => $scope ),
+		site_url( '/', 'https' )
+	);
+}
+
+/**
+ * Print service workers' scripts.
+ */
+function wp_print_service_workers() {
+
+	$scopes = wp_service_workers()->get_scopes();
+	if ( empty( $scopes ) ) {
+		return;
+	}
+	?>
+	<script>
+		if ( navigator.serviceWorker ) {
+			window.addEventListener('load', function() {
+				<?php foreach ( $scopes as $scope ) { ?>
+					navigator.serviceWorker.register(
+						<?php echo wp_json_encode( wp_get_service_worker_url( $scope ) ); ?>,
+						<?php echo wp_json_encode( compact( 'scope' ) ); ?>
+					);
+				<?php } ?>
+			} );
+		}
+	</script>
+	<?php
+}
+
+/**
+ * Register query var.
+ *
+ * @param array $query_vars Query vars.
+ * @return array Query vars.
+ */
+function wp_add_service_worker_query_var( $query_vars ) {
+	$query_vars[] = 'wp_service_worker';
+	return $query_vars;
+}
+
+/**
+ * If it's a service worker script page, display that.
+ */
+function wp_service_worker_loaded() {
+	if ( ! empty( $GLOBALS['wp']->query_vars['wp_service_worker'] ) ) {
+		wp_service_workers()->serve_request( $GLOBALS['wp']->query_vars['wp_service_worker'] );
+		exit;
+	}
+}