diff --git a/includes/class-admin.php b/includes/class-admin.php
index 6b1bf67..bfb924d 100644
--- a/includes/class-admin.php
+++ b/includes/class-admin.php
@@ -23,7 +23,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function dashboard_right_now() {
+	public static function dashboard_right_now(): void {
 		$total_files = wp_count_posts( 'scliveticker_tick' );
 
 		echo '<tr>';
@@ -37,7 +37,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function register_settings_page() {
+	public static function register_settings_page(): void {
 		add_submenu_page(
 			'edit.php?post_type=scliveticker_tick',
 			'Liveticker ' . __( 'Settings', 'stklcode-liveticker' ),
@@ -56,7 +56,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function register_settings() {
+	public static function register_settings(): void {
 		register_setting(
 			'scliveticker_settings',
 			self::OPTION,
@@ -132,7 +132,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function settings_general_section() {
+	public static function settings_general_section(): void {
 	}
 
 	/**
@@ -140,7 +140,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function settings_uninstall_section() {
+	public static function settings_uninstall_section(): void {
 	}
 
 	/**
@@ -148,7 +148,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function settings_enable_ajax_field() {
+	public static function settings_enable_ajax_field(): void {
 		$checked = self::$options['enable_ajax'];
 
 		echo '<input id="' . esc_attr( self::OPTION ) . '-enable-ajax" type="checkbox" name="' . esc_attr( self::OPTION ) . '[enable_ajax]" value="1" ' . checked( $checked, 1, false ) . '> ';
@@ -161,7 +161,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function settings_poll_interval_field() {
+	public static function settings_poll_interval_field(): void {
 		$poll_interval = self::$options['poll_interval'];
 
 		echo '<input id="' . esc_attr( self::OPTION ) . '-poll-interval" type="number" name="' . esc_attr( self::OPTION ) . '[poll_interval]" value="' . esc_attr( $poll_interval ) . '"> ';
@@ -175,7 +175,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function settings_enable_css_field() {
+	public static function settings_enable_css_field(): void {
 		$checked = self::$options['enable_css'];
 
 		echo '<input id="' . esc_attr( self::OPTION ) . '-enable-css" type="checkbox" name="' . esc_attr( self::OPTION ) . '[enable_css]" value="1" ' . checked( $checked, 1, false ) . ' /> ';
@@ -188,7 +188,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function settings_show_feed_field() {
+	public static function settings_show_feed_field(): void {
 		$checked = self::$options['show_feed'];
 
 		echo '<input id="' . esc_attr( self::OPTION ) . '-show-feed" type="checkbox" name="' . esc_attr( self::OPTION ) . '[show_feed]" value="1" ' . checked( $checked, 1, false ) . ' /> ';
@@ -203,7 +203,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @since 1.2
 	 */
-	public static function settings_enable_shortcode_field() {
+	public static function settings_enable_shortcode_field(): void {
 		$checked = self::$options['enable_shortcode'];
 
 		echo '<input id="' . esc_attr( self::OPTION ) . '-enable-shortcode" type="checkbox" name="' . esc_attr( self::OPTION ) . '[enable_shortcode]" value="1" ' . checked( $checked, 1, false ) . ' /> ';
@@ -218,7 +218,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @since 1.2
 	 */
-	public static function settings_embedded_script_field() {
+	public static function settings_embedded_script_field(): void {
 		$checked = self::$options['embedded_script'];
 
 		echo '<input id="' . esc_attr( self::OPTION ) . '-embedded-script" type="checkbox" name="' . esc_attr( self::OPTION ) . '[embedded_script]" value="1" ' . checked( $checked, 1, false ) . ' /> ';
@@ -231,7 +231,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function settings_page() {
+	public static function settings_page(): void {
 		include SCLIVETICKER_DIR . 'views/settings-page.php';
 	}
 
@@ -242,7 +242,7 @@ class Admin extends SCLiveticker {
 	 *
 	 * @return array Parsed arguments.
 	 */
-	public static function validate_settings( $input ) {
+	public static function validate_settings( array $input ): array {
 		$defaults = self::default_options();
 
 		$result['enable_ajax']      = isset( $input['enable_ajax'] ) ? intval( $input['enable_ajax'] ) : 0;
@@ -261,7 +261,7 @@ class Admin extends SCLiveticker {
 	 * @return void
 	 * @since 1.1
 	 */
-	public static function register_block() {
+	public static function register_block(): void {
 		wp_register_script(
 			'scliveticker-editor',
 			SCLIVETICKER_BASE . 'scripts/block.min.js',
diff --git a/includes/class-api.php b/includes/class-api.php
index 0feb0d3..1a3f226 100644
--- a/includes/class-api.php
+++ b/includes/class-api.php
@@ -15,6 +15,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 }
 
 use DateTime;
+use WP_REST_Request;
 
 /**
  * Liveticker.
@@ -27,7 +28,7 @@ class Api {
 	 *
 	 * @return void
 	 */
-	public static function init() {
+	public static function init(): void {
 		// Add rendered modification date to WP_Post object.
 		register_rest_field(
 			'scliveticker_tick',
@@ -47,12 +48,12 @@ class Api {
 	/**
 	 * Filter tick queries by ticker slug and date.
 	 *
-	 * @param array            $args    Query vars.
-	 * @param \WP_REST_Request $request The REST request.
+	 * @param array           $args    Query vars.
+	 * @param WP_REST_Request $request The REST request.
 	 *
 	 * @return array Filtered query values.
 	 */
-	public static function tick_query_filter( $args, $request ) {
+	public static function tick_query_filter( array $args, WP_REST_Request $request ): array {
 		// Extract arguments.
 		$ticker_slug = $request->get_param( 'ticker' );
 		$limit       = intval( $request->get_param( 'limit' ) );
diff --git a/includes/class-scliveticker.php b/includes/class-scliveticker.php
index 89ab174..c24dfaa 100644
--- a/includes/class-scliveticker.php
+++ b/includes/class-scliveticker.php
@@ -62,7 +62,7 @@ class SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function init() {
+	public static function init(): void {
 		// Skip on autosave.
 		if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
 			return;
@@ -114,7 +114,7 @@ class SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function register_types() {
+	public static function register_types(): void {
 		// Add new taxonomy, make it hierarchical (like categories).
 		$labels = array(
 			'name'              => _x( 'Ticker', 'taxonomy general name', 'stklcode-liveticker' ),
@@ -182,7 +182,7 @@ class SCLiveticker {
 	 *
 	 * @return string
 	 */
-	public static function shortcode_ticker_show( $atts ) {
+	public static function shortcode_ticker_show( array $atts ): string {
 		// Indicate presence of shortcode (to enqueue styles/scripts later).
 		self::$shortcode_present = true;
 
@@ -259,7 +259,7 @@ class SCLiveticker {
 	 * @return void
 	 * @since 1.1 Combined former methods "enqueue_styles" and "enqueue_scripts".
 	 */
-	public static function enqueue_resources() {
+	public static function enqueue_resources(): void {
 		// Only add if shortcode is present.
 		if ( self::$shortcode_present || self::$widget_present || self::block_present() ) {
 			wp_enqueue_script(
@@ -301,7 +301,7 @@ class SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function ajax_update() {
+	public static function ajax_update(): void {
 		// Verify AJAX nonce.
 		check_ajax_referer( 'scliveticker_update-ticks' );
 
@@ -394,7 +394,7 @@ class SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function mark_widget_present() {
+	public static function mark_widget_present(): void {
 		self::$widget_present = true;
 	}
 
@@ -405,7 +405,7 @@ class SCLiveticker {
 	 *
 	 * @return void
 	 */
-	protected static function update_options( $options = null ) {
+	protected static function update_options( ?array $options = null ): void {
 		self::$options = wp_parse_args(
 			get_option( self::OPTION ),
 			self::default_options()
@@ -417,7 +417,7 @@ class SCLiveticker {
 	 *
 	 * @return array The options array.
 	 */
-	protected static function default_options() {
+	protected static function default_options(): array {
 		return array(
 			'enable_ajax'      => 1,
 			'poll_interval'    => 60,
@@ -439,7 +439,7 @@ class SCLiveticker {
 	 *
 	 * @return string HTML code of tick.
 	 */
-	private static function tick_html( $time, $title, $content, $id ) {
+	private static function tick_html( string $time, string $title, string $content, int $id ): string {
 		if ( self::$options['enable_shortcode'] ) {
 			$content = do_shortcode( $content );
 		}
@@ -460,7 +460,7 @@ class SCLiveticker {
 	 *
 	 * @return string HTML code of widget tick.
 	 */
-	public static function tick_html_widget( $time, $title, $highlight, $id = 0 ) {
+	public static function tick_html_widget( string $time, string $title, bool $highlight, int $id = 0 ): string {
 		$out = '<li';
 		if ( $highlight ) {
 			$out .= ' class="sclt-widget-new"';
@@ -480,7 +480,7 @@ class SCLiveticker {
 	 * @return boolean True, if Gutenberg block is present.
 	 * @since 1.1
 	 */
-	private static function block_present() {
+	private static function block_present(): bool {
 		return function_exists( 'has_block' ) && // We are in WP 5.x environment.
 			has_block( 'scliveticker/ticker' ); // Specific block is present.
 	}
diff --git a/includes/class-system.php b/includes/class-system.php
index 5810bde..807fab4 100644
--- a/includes/class-system.php
+++ b/includes/class-system.php
@@ -28,7 +28,7 @@ class System extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function activate() {
+	public static function activate(): void {
 		// Load current options.
 		self::update_options();
 
@@ -49,7 +49,7 @@ class System extends SCLiveticker {
 	 *
 	 * @return void
 	 */
-	public static function uninstall() {
+	public static function uninstall(): void {
 		// Delete all ticks.
 		$ticks = new WP_Query( array( 'post_type' => 'scliveticker_tick' ) );
 		foreach ( $ticks->get_posts() as $tick ) {
diff --git a/includes/class-widget.php b/includes/class-widget.php
index 1a1c65c..d738fcf 100644
--- a/includes/class-widget.php
+++ b/includes/class-widget.php
@@ -31,7 +31,7 @@ class Widget extends WP_Widget {
 	/**
 	 * Register the widget.
 	 */
-	public static function register() {
+	public static function register(): void {
 		register_widget( __CLASS__ );
 	}
 
@@ -164,7 +164,7 @@ class Widget extends WP_Widget {
 	 *
 	 * @return array Complete instance configuration.
 	 */
-	private static function fill_options_with_defaults( $instance ) {
+	private static function fill_options_with_defaults( array $instance ): array {
 		$default = array(
 			'title'          => '',
 			'category'       => '',
diff --git a/stklcode-liveticker.php b/stklcode-liveticker.php
index 9a775a9..c59615f 100644
--- a/stklcode-liveticker.php
+++ b/stklcode-liveticker.php
@@ -68,7 +68,7 @@ spl_autoload_register( 'scliveticker_autoload' );
  *
  * @return void
  */
-function scliveticker_autoload( $class_name ) {
+function scliveticker_autoload( string $class_name ): void {
 	$plugin_classes = array(
 		'SCLiveticker\\SCLiveticker',
 		'SCLiveticker\\Admin',
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 482f425..ede8667 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -28,7 +28,7 @@ require_once "{$_tests_dir}/includes/functions.php";
 /**
  * Manually load the plugin being tested.
  */
-function _manually_load_plugin() {
+function _manually_load_plugin(): void {
 	require dirname( dirname( __FILE__ ) ) . '/stklcode-liveticker.php';
 }
 
diff --git a/tests/test-api.php b/tests/test-api.php
index 0ee8ea8..f78f0cb 100644
--- a/tests/test-api.php
+++ b/tests/test-api.php
@@ -24,7 +24,7 @@ class Test_API extends WP_UnitTestCase {
 	 *
 	 * @return void
 	 */
-	public function set_up() {
+	public function set_up(): void {
 		parent::set_up();
 		global $wp_rest_server;
 		$wp_rest_server = new WP_REST_Server();
@@ -36,7 +36,7 @@ class Test_API extends WP_UnitTestCase {
 	 *
 	 * @return void
 	 */
-	public function test_register_route() {
+	public function test_register_route(): void {
 		global $wp_rest_server;
 
 		$routes = $wp_rest_server->get_routes();
@@ -52,7 +52,7 @@ class Test_API extends WP_UnitTestCase {
 	 *
 	 * @return void
 	 */
-	public function test_get_ticks() {
+	public function test_get_ticks(): void {
 		global $wp_rest_server;
 
 		$request  = new WP_REST_Request( 'GET', '/wp/v2/scliveticker_tick' );