diff --git a/inc/class-statify-api.php b/inc/class-statify-api.php
index 99e69f9..c609bc6 100644
--- a/inc/class-statify-api.php
+++ b/inc/class-statify-api.php
@@ -31,7 +31,7 @@ class Statify_Api extends Statify {
 	 *
 	 * @return void
 	 */
-	public static function init() {
+	public static function init(): void {
 		if ( Statify::is_javascript_tracking_enabled() ) {
 			register_rest_route(
 				self::REST_NAMESPACE,
@@ -88,7 +88,7 @@ public static function check_authentication( $errors ) {
 	 *
 	 * @return WP_REST_Response The response.
 	 */
-	public static function track_visit( $request ) {
+	public static function track_visit( WP_REST_Request $request ): WP_REST_Response {
 		// Only do something if snippet use is actually configured.
 		if ( Statify::is_javascript_tracking_enabled() ) {
 			// Nonce verification, if necessary. We do not rely on the WP REST default mechanisms.
@@ -121,7 +121,7 @@ public static function track_visit( $request ) {
 	 *
 	 * @return WP_REST_Response The response.
 	 */
-	public static function get_stats( $request ) {
+	public static function get_stats( WP_REST_Request $request ): WP_REST_Response {
 		$refresh = '1' === $request->get_param( 'refresh' );
 
 		$stats  = Statify_Dashboard::get_stats( $refresh );
diff --git a/inc/class-statify-backend.php b/inc/class-statify-backend.php
index 5c8209d..24ad963 100644
--- a/inc/class-statify-backend.php
+++ b/inc/class-statify-backend.php
@@ -29,7 +29,7 @@ class Statify_Backend {
 	 *
 	 * @return  array           Merged links
 	 */
-	public static function add_meta_link( $input, $file ) {
+	public static function add_meta_link( array $input, string $file ): array {
 
 		// Other plugins?
 		if ( STATIFY_BASE !== $file ) {
@@ -55,7 +55,7 @@ public static function add_meta_link( $input, $file ) {
 	 *
 	 * @return  array           Merged links
 	 */
-	public static function add_action_link( $input ) {
+	public static function add_action_link( array $input ): array {
 
 		// Rights?
 		if ( ! current_user_can( 'manage_options' ) ) {
diff --git a/inc/class-statify-cron.php b/inc/class-statify-cron.php
index 969c770..7d53e05 100644
--- a/inc/class-statify-cron.php
+++ b/inc/class-statify-cron.php
@@ -24,7 +24,7 @@ class Statify_Cron extends Statify {
 	 * @since    0.3.0
 	 * @version  1.4.0
 	 */
-	public static function cleanup_data() {
+	public static function cleanup_data(): void {
 
 		// Global.
 		global $wpdb;
diff --git a/inc/class-statify-dashboard.php b/inc/class-statify-dashboard.php
index cf8f7c4..00bdaa7 100755
--- a/inc/class-statify-dashboard.php
+++ b/inc/class-statify-dashboard.php
@@ -31,7 +31,7 @@ class Statify_Dashboard extends Statify {
 	 *
 	 * @since   0.1.0
 	 */
-	public static function init() {
+	public static function init(): void {
 
 		// Filter user_can_see_stats.
 		if ( ! self::user_can_see_stats() ) {
@@ -72,7 +72,7 @@ public static function init() {
 	 * @since   0.1.0
 	 * @version 1.4.0
 	 */
-	public static function add_style() {
+	public static function add_style(): void {
 
 		// Register CSS.
 		wp_register_style(
@@ -106,7 +106,7 @@ public static function add_style() {
 	 * @since    0.1.0
 	 * @version  1.4.0
 	 */
-	public static function add_js() {
+	public static function add_js(): void {
 
 		// Register JS.
 		wp_register_script(
@@ -155,7 +155,7 @@ public static function add_js() {
 	 * @since    0.1.0
 	 * @version  1.4.0
 	 */
-	public static function print_frontview() {
+	public static function print_frontview(): void {
 
 		// Load JS.
 		wp_enqueue_script( 'chartist_js' );
@@ -174,7 +174,7 @@ public static function print_frontview() {
 	 * @since    0.4.0
 	 * @version  1.4.0
 	 */
-	public static function print_backview() {
+	public static function print_backview(): void {
 
 		// Capability check.
 		if ( ! current_user_can( 'edit_dashboard' ) ) {
@@ -203,7 +203,7 @@ public static function print_backview() {
 	 *
 	 * @return void
 	 */
-	private static function _save_widget_options() {
+	private static function _save_widget_options(): void {
 		// Check the nonce field from the dashboard form.
 		if ( ! check_admin_referer( 'statify-dashboard' ) ) {
 			return;
@@ -248,7 +248,7 @@ private static function _save_widget_options() {
 	 * @since    1.4.0
 	 * @version  1.4.0
 	 */
-	private static function _get_version() {
+	private static function _get_version(): void {
 
 		// Get plugin meta.
 		$meta = get_plugin_data( STATIFY_FILE );
@@ -267,7 +267,7 @@ private static function _get_version() {
 	 *
 	 * @return  array  $data  stats data from cache or database
 	 */
-	public static function get_stats( $force_refresh = false ) {
+	public static function get_stats( bool $force_refresh = false ): array {
 
 		// Get from cache if enabled.
 		if ( ! $force_refresh ) {
@@ -304,7 +304,7 @@ public static function get_stats( $force_refresh = false ) {
 	 *
 	 * @return  array  DB results
 	 */
-	private static function _select_data() {
+	private static function _select_data(): array {
 
 		// Global.
 		global $wpdb;
diff --git a/inc/class-statify-deactivate.php b/inc/class-statify-deactivate.php
index bdfce5b..b906c7d 100644
--- a/inc/class-statify-deactivate.php
+++ b/inc/class-statify-deactivate.php
@@ -24,7 +24,7 @@ class Statify_Deactivate {
 	 * @since    1.4.0
 	 * @version  1.4.0
 	 */
-	public static function init() {
+	public static function init(): void {
 
 		// Delete transients.
 		delete_transient( 'statify_data' );
diff --git a/inc/class-statify-frontend.php b/inc/class-statify-frontend.php
index 0521bbb..278a657 100644
--- a/inc/class-statify-frontend.php
+++ b/inc/class-statify-frontend.php
@@ -27,7 +27,7 @@ class Statify_Frontend extends Statify {
 	 *
 	 * @return void
 	 */
-	public static function track_visit() {
+	public static function track_visit(): void {
 		if ( self::is_javascript_tracking_enabled() ) {
 			return;
 		}
@@ -55,7 +55,7 @@ public static function track_visit() {
 	 *
 	 * @return  array  $vars  Output with plugin variables
 	 */
-	public static function query_vars( $vars ) {
+	public static function query_vars( array $vars ): array {
 		$vars[] = 'statify_referrer';
 		$vars[] = 'statify_target';
 
@@ -69,7 +69,7 @@ public static function query_vars( $vars ) {
 	 * @since    1.1.0
 	 * @version  1.4.1
 	 */
-	public static function wp_footer() {
+	public static function wp_footer(): void {
 		// JS tracking disabled or AMP is used for the current request.
 		if (
 			! self::is_javascript_tracking_enabled() ||
@@ -109,11 +109,7 @@ public static function wp_footer() {
 	 *
 	 * @param array $analytics_entries Analytics entries.
 	 */
-	public static function amp_analytics_entries( $analytics_entries ) {
-		if ( ! is_array( $analytics_entries ) ) {
-			$analytics_entries = array();
-		}
-
+	public static function amp_analytics_entries( array $analytics_entries ): array {
 		// Analytics script is only relevant, if "JS" tracking is enabled, to prevent double tracking.
 		if ( self::is_javascript_tracking_enabled() ) {
 			$analytics_entries['statify'] = array(
@@ -132,11 +128,7 @@ public static function amp_analytics_entries( $analytics_entries ) {
 	 *
 	 * @param array $analytics Analytics.
 	 */
-	public static function amp_post_template_analytics( $analytics ) {
-		if ( ! is_array( $analytics ) ) {
-			$analytics = array();
-		}
-
+	public static function amp_post_template_analytics( array $analytics ): array {
 		// Analytics script is only relevant, if "JS" tracking is enabled, to prevent double tracking.
 		if ( self::is_javascript_tracking_enabled() ) {
 			$analytics['statify'] = array(
@@ -154,7 +146,7 @@ public static function amp_post_template_analytics( $analytics ) {
 	 *
 	 * @return array Configuration array.
 	 */
-	private static function make_amp_config() {
+	private static function make_amp_config(): array {
 		$cfg = array(
 			'requests'       => array(
 				'pageview' => rest_url( Statify_Api::REST_NAMESPACE . '/' . Statify_Api::REST_ROUTE_TRACK ),
diff --git a/inc/class-statify-install.php b/inc/class-statify-install.php
index ee7ecf4..3c2ad7e 100644
--- a/inc/class-statify-install.php
+++ b/inc/class-statify-install.php
@@ -26,7 +26,7 @@ class Statify_Install {
 	 *
 	 * @param bool $network_wide Whether the plugin was activated network-wide or not.
 	 */
-	public static function init( $network_wide = false ) {
+	public static function init( bool $network_wide = false ): void {
 
 		if ( $network_wide && is_multisite() ) {
 			$sites = get_sites();
@@ -53,9 +53,9 @@ public static function init( $network_wide = false ) {
 	 *
 	 * @param int $site_id Site ID.
 	 */
-	public static function init_site( $site_id ) {
+	public static function init_site( int $site_id ): void {
 
-		switch_to_blog( (int) $site_id );
+		switch_to_blog( $site_id );
 
 		self::_apply();
 
@@ -68,7 +68,7 @@ public static function init_site( $site_id ) {
 	 * @since   0.1.0
 	 * @version 1.4.0
 	 */
-	private static function _apply() {
+	private static function _apply(): void {
 
 		// Cleanup any leftover transients.
 		delete_transient( 'statify_data' );
diff --git a/inc/class-statify-settings.php b/inc/class-statify-settings.php
index 4e12bce..22da285 100755
--- a/inc/class-statify-settings.php
+++ b/inc/class-statify-settings.php
@@ -23,7 +23,7 @@ class Statify_Settings {
 	 *
 	 * @return void
 	 */
-	public static function register_settings() {
+	public static function register_settings(): void {
 		register_setting( 'statify', 'statify', array( __CLASS__, 'sanitize_options' ) );
 
 		// Global settings.
@@ -127,7 +127,7 @@ public static function register_settings() {
 	 *
 	 * @return void
 	 */
-	public static function options_days() {
+	public static function options_days(): void {
 		?>
 		<input id="statify-days" name="statify[days]" type="number" min="1" value="<?php echo esc_attr( Statify::$_options['days'] ); ?>">
 		<?php esc_html_e( 'days', 'statify' ); ?>
@@ -140,7 +140,7 @@ public static function options_days() {
 	 *
 	 * @return void
 	 */
-	public static function options_snippet() {
+	public static function options_snippet(): void {
 		?>
 		<p>
 			<?php self::show_snippet_option( Statify::TRACKING_METHOD_DEFAULT, __( 'Default tracking', 'statify' ) ); ?>
@@ -162,7 +162,7 @@ public static function options_snippet() {
 	 * @param int    $value the value for the input radio.
 	 * @param string $label the label.
 	 */
-	private static function show_snippet_option( $value, $label ) {
+	private static function show_snippet_option( int $value, string $label ): void {
 		?>
 			<label>
 				<input name="statify[snippet]" type="radio" value="<?php echo esc_html( $value ); ?>" <?php checked( Statify::$_options['snippet'], $value ); ?>>
@@ -176,7 +176,7 @@ private static function show_snippet_option( $value, $label ) {
 	 *
 	 * @return void
 	 */
-	public static function header_dashboard() {
+	public static function header_dashboard(): void {
 		?>
 		<p>
 			<?php esc_html_e( 'The following options affect the admin dashboard widget.', 'statify' ); ?>
@@ -189,7 +189,7 @@ public static function header_dashboard() {
 	 *
 	 * @return void
 	 */
-	public static function options_days_show() {
+	public static function options_days_show(): void {
 		?>
 		<input id="statify-days-show" name="statify[days_show]" type="number" min="1" value="<?php echo esc_attr( Statify::$_options['days_show'] ); ?>">
 		<?php esc_html_e( 'days', 'statify' ); ?>
@@ -202,7 +202,7 @@ public static function options_days_show() {
 	 *
 	 * @return void
 	 */
-	public static function options_limit() {
+	public static function options_limit(): void {
 		?>
 		<input id="statify-limit" name="statify[limit]" type="number" min="1" max="100" value="<?php echo esc_attr( Statify::$_options['limit'] ); ?>">
 		(<?php esc_html_e( 'Default', 'statify' ); ?>: 3)
@@ -214,7 +214,7 @@ public static function options_limit() {
 	 *
 	 * @return void
 	 */
-	public static function options_today() {
+	public static function options_today(): void {
 		?>
 		<input  id="statify-today" type="checkbox" name="statify[today]" value="1" <?php checked( Statify::$_options['today'], 1 ); ?>>
 		(<?php esc_html_e( 'Default', 'statify' ); ?>: <?php esc_html_e( 'No', 'statify' ); ?>)
@@ -226,7 +226,7 @@ public static function options_today() {
 	 *
 	 * @return void
 	 */
-	public static function options_show_totals() {
+	public static function options_show_totals(): void {
 		?>
 		<input  id="statify-show-totals" type="checkbox" name="statify[show_totals]" value="1" <?php checked( Statify::$_options['show_totals'], 1 ); ?>>
 		(<?php esc_html_e( 'Default', 'statify' ); ?>: <?php esc_html_e( 'No', 'statify' ); ?>)
@@ -240,7 +240,7 @@ public static function options_show_totals() {
 	 *
 	 * @return void
 	 */
-	public static function options_show_widget_roles() {
+	public static function options_show_widget_roles(): void {
 		$all_roles = apply_filters( 'statify__available_roles', wp_roles()->roles );
 
 		// Backwards compatibility for older statify versions without this option.
@@ -266,12 +266,12 @@ public static function options_show_widget_roles() {
 	 *
 	 * @param string $input_id the name for the input element id.
 	 * @param string $name the name for the input element name attribute.
-	 * @param array  $available_roles the list of all available roles to be listes with checkbox.
+	 * @param array  $available_roles the list of all available roles to be listed with checkbox.
 	 * @param array  $saved_roles the list of all role names that should be checked.
 	 *
 	 * @return void
 	 */
-	private static function show_roles_list( $input_id, $name, $available_roles, $saved_roles = array() ) {
+	private static function show_roles_list( string $input_id, string $name, array $available_roles, array $saved_roles = array() ): void {
 		foreach ( $available_roles as $role => $role_object ) {
 			?>
 			<p><label for="statify-<?php echo esc_html( $input_id ); ?>-<?php echo esc_html( $role ); ?>">
@@ -295,7 +295,7 @@ private static function show_roles_list( $input_id, $name, $available_roles, $sa
 	 *
 	 * @return void
 	 */
-	public static function header_skip() {
+	public static function header_skip(): void {
 		?>
 		<p>
 			<?php echo wp_kses( __( 'The following options define cases in which a view will <strong>not</strong> be tracked.', 'statify' ), array( 'strong' => array() ) ); ?>
@@ -308,7 +308,7 @@ public static function header_skip() {
 	 *
 	 * @return void
 	 */
-	public static function options_skip_blacklist() {
+	public static function options_skip_blacklist(): void {
 		?>
 		<input id="statify-skip-referrer" type="checkbox" name="statify[blacklist]" value="1"<?php checked( Statify::$_options['blacklist'] ); ?>>
 		(<?php esc_html_e( 'Default', 'statify' ); ?>: <?php esc_html_e( 'No', 'statify' ); ?>)
@@ -321,7 +321,7 @@ public static function options_skip_blacklist() {
 	 *
 	 * @return void
 	 */
-	public static function options_skip_logged_in() {
+	public static function options_skip_logged_in(): void {
 		?>
 		<select id="statify-skip-logged_in" name="statify[skip][logged_in]">
 			<option value="0" <?php selected( Statify::$_options['skip']['logged_in'], 0 ); ?>><?php esc_html_e( 'Track all users', 'statify' ); ?></option>
@@ -345,7 +345,7 @@ public static function options_skip_logged_in() {
 	 *
 	 * @return void
 	 */
-	public static function action_update_options( $old_value, $value ) {
+	public static function action_update_options( array $old_value, array $value ): void {
 		// Delete transient.
 		delete_transient( 'statify_data' );
 
@@ -364,7 +364,7 @@ public static function action_update_options( $old_value, $value ) {
 	 *
 	 * @return array Validated and sanitized options.
 	 */
-	public static function sanitize_options( $options ) {
+	public static function sanitize_options( array $options ): array {
 
 		// Sanitize numeric values.
 		$res = array();
@@ -432,7 +432,7 @@ public static function sanitize_options( $options ) {
 	 *
 	 * @return void
 	 */
-	public static function add_admin_menu() {
+	public static function add_admin_menu(): void {
 		add_options_page(
 			__( 'Statify', 'statify' ),
 			__( 'Statify', 'statify' ),
@@ -447,7 +447,7 @@ public static function add_admin_menu() {
 	 *
 	 * @return void
 	 */
-	public static function create_settings_page() {
+	public static function create_settings_page(): void {
 		?>
 
 		<div class="wrap">
diff --git a/inc/class-statify-table.php b/inc/class-statify-table.php
index 05b375c..2a93e50 100644
--- a/inc/class-statify-table.php
+++ b/inc/class-statify-table.php
@@ -24,7 +24,7 @@ class Statify_Table {
 	 * @since   0.6.0
 	 * @version 1.2.4
 	 */
-	public static function init() {
+	public static function init(): void {
 
 		// Global.
 		global $wpdb;
@@ -46,7 +46,7 @@ public static function init() {
 	 * @since   0.6.0
 	 * @version 1.2.4
 	 */
-	public static function create() {
+	public static function create(): void {
 
 		global $wpdb;
 
@@ -80,7 +80,7 @@ public static function create() {
 	 * @since   0.6.0
 	 * @version 1.2.4
 	 */
-	public static function drop() {
+	public static function drop(): void {
 
 		global $wpdb;
 
diff --git a/inc/class-statify-uninstall.php b/inc/class-statify-uninstall.php
index f9f1cb3..db7c100 100644
--- a/inc/class-statify-uninstall.php
+++ b/inc/class-statify-uninstall.php
@@ -24,7 +24,7 @@ class Statify_Uninstall {
 	 * @since   0.1.0
 	 * @version 0.1.0
 	 */
-	public static function init() {
+	public static function init(): void {
 		if ( is_multisite() ) {
 			$old   = get_current_blog_id();
 			$sites = get_sites();
@@ -50,7 +50,7 @@ public static function init() {
 	 *
 	 * @param int $site_id Site ID.
 	 */
-	public static function init_site( $site_id ) {
+	public static function init_site( int $site_id ): void {
 
 		switch_to_blog( $site_id );
 
@@ -65,7 +65,7 @@ public static function init_site( $site_id ) {
 	 * @since   0.1.0
 	 * @version 1.4.0
 	 */
-	private static function _apply() {
+	private static function _apply(): void {
 
 		// Delete options.
 		delete_option( 'statify' );
diff --git a/inc/class-statify.php b/inc/class-statify.php
index 008e85e..9683a7d 100755
--- a/inc/class-statify.php
+++ b/inc/class-statify.php
@@ -38,7 +38,7 @@ class Statify {
 	 *
 	 * @since    1.7 Replaces previously used instance() and __construct().
 	 */
-	public static function init() {
+	public static function init(): void {
 		// Nothing to do on autosave.
 		if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
 			return;
@@ -103,7 +103,7 @@ public static function init() {
 	 * @since  1.7.0 $is_snippet parameter added.
 	 * @since  2.0.0 Migration from Statify_Frontend::track_visit to Statify::track with multiple parameters.
 	 */
-	protected static function track( $referrer, $target ) {
+	protected static function track( ?string $referrer, ?string $target ): void {
 		// Fallbacks for uninitialized or omitted target and referrer values.
 		if ( is_null( $target ) ) {
 			$target = '/';
@@ -173,7 +173,7 @@ protected static function track( $referrer, $target ) {
 	 *
 	 * @since 1.7.3
 	 */
-	public static function parse_date( $date ) {
+	public static function parse_date( string $date ): string {
 		if ( function_exists( 'wp_date' ) ) { // Exists since WP 5.3.
 			return wp_date( get_option( 'date_format' ), strtotime( $date ) );
 		}
@@ -186,7 +186,7 @@ public static function parse_date( $date ) {
 	 *
 	 * @return bool true if and only if one of the JavaScript tracking options is enabled.
 	 */
-	public static function is_javascript_tracking_enabled() {
+	public static function is_javascript_tracking_enabled(): bool {
 		return in_array(
 			self::$_options['snippet'],
 			array(
@@ -207,7 +207,7 @@ public static function is_javascript_tracking_enabled() {
 	 * @hook  boolean  statify__user_can_see_stats
 	 * @see   https://wordpress.org/plugins/statify/
 	 */
-	public static function user_can_see_stats() {
+	public static function user_can_see_stats(): bool {
 		if ( isset( self::$_options['show_widget_roles'] ) ) {
 			$statify_roles = self::$_options['show_widget_roles'];
 			$current_user = wp_get_current_user();
@@ -236,7 +236,7 @@ public static function user_can_see_stats() {
 	 * @since  1.2.6
 	 * @since  2.0.0 Migration from Statify_Frontend to Statify class.
 	 */
-	private static function skip_tracking() {
+	private static function skip_tracking(): bool {
 		if ( function_exists( 'apply_filters_deprecated' ) ) {
 			apply_filters_deprecated( 'statify_skip_tracking', array( '' ), '1.5.0', 'statify__skip_tracking' );
 		}
@@ -283,7 +283,7 @@ private static function skip_tracking() {
 	 * @since 1.7.0
 	 * @since 2.0.0 Migration from Statify_Frontend to Statify class, removed $user_agent parameter.
 	 */
-	private static function is_bot() {
+	private static function is_bot(): bool {
 		$crawler_detect = new \Jaybizzle\CrawlerDetect\CrawlerDetect();
 
 		// Check the user agent of the current 'visitor' via the user agent and http_from header.
@@ -298,7 +298,7 @@ private static function is_bot() {
 	 * @since 1.6.1
 	 * @since 1.9.0 Migration from Statify_Frontend to Statify class.
 	 */
-	protected static function is_internal() {
+	protected static function is_internal(): bool {
 		// Skip for preview, 404 calls, feed, search, favicon and sitemap access.
 		return is_preview() || is_404() || is_feed() || is_search()
 			|| ( function_exists( 'is_favicon' ) && is_favicon() )
@@ -314,7 +314,7 @@ protected static function is_internal() {
 	 * @since 1.5.0
 	 * @since 1.9.0 Migration from Statify_Frontend to Statify class.
 	 */
-	private static function check_referrer() {
+	private static function check_referrer(): bool {
 		// Return false if the disallowed-keys filter (formerly blacklist) is inactive.
 		if ( ! self::$_options['blacklist'] ) {
 			return false;
@@ -357,7 +357,7 @@ private static function check_referrer() {
 	 * @since 1.7.3 Renamed to "get_disallowed_keys" to match WP 5.5. wording.
 	 * @since 1.9.0 Migration from Statify_Frontend to Statify class.
 	 */
-	private static function get_disallowed_keys() {
+	private static function get_disallowed_keys(): array {
 		$disallowed_keys = get_option( 'disallowed_keys' );
 
 		if ( false === $disallowed_keys ) {
@@ -383,7 +383,7 @@ private static function get_disallowed_keys() {
 	 *
 	 * @return boolean
 	 */
-	private static function strposa( $haystack, array $needle, $offset = 0 ) {
+	private static function strposa( string $haystack, array $needle, int $offset = 0 ): bool {
 
 		foreach ( $needle as $query ) {
 			if ( strpos( $haystack, $query, $offset ) !== false ) {