diff --git a/includes/ApiCategoryTree.php b/includes/ApiCategoryTree.php
index 5297db47..b5c7bf7a 100644
--- a/includes/ApiCategoryTree.php
+++ b/includes/ApiCategoryTree.php
@@ -32,33 +32,15 @@ use Wikimedia\Rdbms\IConnectionProvider;
  */
 
 class ApiCategoryTree extends ApiBase {
-	/** @var ConfigFactory */
-	private $configFactory;
+	private ConfigFactory $configFactory;
+	private LanguageConverterFactory $languageConverterFactory;
+	private LinkRenderer $linkRenderer;
+	private IConnectionProvider $dbProvider;
+	private WANObjectCache $wanCache;
 
-	/** @var LanguageConverterFactory */
-	private $languageConverterFactory;
-
-	/** @var LinkRenderer */
-	private $linkRenderer;
-
-	/** @var IConnectionProvider */
-	private $dbProvider;
-
-	/** @var WANObjectCache */
-	private $wanCache;
-
-	/**
-	 * @param ApiMain $main
-	 * @param string $action
-	 * @param ConfigFactory $configFactory
-	 * @param IConnectionProvider $dbProvider
-	 * @param LanguageConverterFactory $languageConverterFactory
-	 * @param LinkRenderer $linkRenderer
-	 * @param WANObjectCache $wanCache
-	 */
 	public function __construct(
 		ApiMain $main,
-		$action,
+		string $action,
 		ConfigFactory $configFactory,
 		IConnectionProvider $dbProvider,
 		LanguageConverterFactory $languageConverterFactory,
@@ -102,7 +84,7 @@ class ApiCategoryTree extends ApiBase {
 	 * @param array $params
 	 * @return string[]
 	 */
-	private function extractOptions( $params ): array {
+	private function extractOptions( array $params ): array {
 		if ( !isset( $params['options'] ) ) {
 			return [];
 		}
@@ -157,7 +139,7 @@ class ApiCategoryTree extends ApiBase {
 	 * @param Config $ctConfig Config for CategoryTree
 	 * @return string HTML
 	 */
-	private function getHTML( CategoryTree $ct, Title $title, $depth, Config $ctConfig ) {
+	private function getHTML( CategoryTree $ct, Title $title, int $depth, Config $ctConfig ): string {
 		$langConv = $this->languageConverterFactory->getLanguageConverter();
 
 		return $this->wanCache->getWithSetCallback(
diff --git a/includes/CategoryCache.php b/includes/CategoryCache.php
index 42f5552c..8f225557 100644
--- a/includes/CategoryCache.php
+++ b/includes/CategoryCache.php
@@ -30,14 +30,10 @@ use Wikimedia\Rdbms\IResultWrapper;
  */
 class CategoryCache {
 	/** @var (?Category)[] Keys are category database names, values are either a Category object or null */
-	private $cache = [];
+	private array $cache = [];
 
-	/** @var ILoadBalancer */
-	private $loadBalancer;
+	private ILoadBalancer $loadBalancer;
 
-	/**
-	 * @param ILoadBalancer $loadBalancer
-	 */
 	public function __construct(
 		ILoadBalancer $loadBalancer
 	) {
@@ -47,8 +43,6 @@ class CategoryCache {
 	/**
 	 * Get a preloaded Category object or null when the Category does not exists. Loaded the Category on demand,
 	 * if not in cache, use self::doQuery when requesting a high number of category
-	 * @param LinkTarget $categoryTarget
-	 * @return ?Category
 	 */
 	public function getCategory( LinkTarget $categoryTarget ): ?Category {
 		if ( $categoryTarget->getNamespace() !== NS_CATEGORY ) {
@@ -95,10 +89,7 @@ class CategoryCache {
 		$this->fillFromQuery( $rows );
 	}
 
-	/**
-	 * @param IResultWrapper $rows
-	 */
-	public function fillFromQuery( IResultWrapper $rows ) {
+	public function fillFromQuery( IResultWrapper $rows ): void {
 		foreach ( $rows as $row ) {
 			$this->cache[$row->cat_title] = Category::newFromRow( $row );
 		}
diff --git a/includes/CategoryTree.php b/includes/CategoryTree.php
index fe85a47e..5aeaff9f 100644
--- a/includes/CategoryTree.php
+++ b/includes/CategoryTree.php
@@ -44,24 +44,11 @@ use Wikimedia\Rdbms\IConnectionProvider;
  * to display the category structure of a wiki
  */
 class CategoryTree {
-	/** @var OptionManager */
-	public $optionManager;
+	public OptionManager $optionManager;
+	private Config $config;
+	private IConnectionProvider $dbProvider;
+	private LinkRenderer $linkRenderer;
 
-	/** @var Config */
-	private $config;
-
-	/** @var IConnectionProvider */
-	private $dbProvider;
-
-	/** @var LinkRenderer */
-	private $linkRenderer;
-
-	/**
-	 * @param array $options
-	 * @param Config $config
-	 * @param IConnectionProvider $dbProvider
-	 * @param LinkRenderer $linkRenderer
-	 */
 	public function __construct(
 		array $options,
 		Config $config,
@@ -76,9 +63,8 @@ class CategoryTree {
 
 	/**
 	 * Add ResourceLoader modules to the OutputPage object
-	 * @param OutputPage $outputPage
 	 */
-	public static function setHeaders( OutputPage $outputPage ) {
+	public static function setHeaders( OutputPage $outputPage ): void {
 		# Add the modules
 		$outputPage->addModuleStyles( 'ext.categoryTree.styles' );
 		$outputPage->addModules( 'ext.categoryTree' );
@@ -95,8 +81,8 @@ class CategoryTree {
 	 * @param bool $allowMissing
 	 * @return bool|string
 	 */
-	public function getTag( ?Parser $parser, $category, $hideroot = false, array $attr = [],
-		$depth = 1, $allowMissing = false
+	public function getTag( ?Parser $parser, string $category, bool $hideroot = false, array $attr = [],
+		int $depth = 1, bool $allowMissing = false
 	) {
 		$disableCache = $this->config->get( 'CategoryTreeDisableCache' );
 
@@ -147,12 +133,9 @@ class CategoryTree {
 
 	/**
 	 * Returns a string with an HTML representation of the children of the given category.
-	 * @param Title $title
-	 * @param int $depth
 	 * @suppress PhanUndeclaredClassMethod,PhanUndeclaredClassInstanceof
-	 * @return string
 	 */
-	public function renderChildren( Title $title, $depth = 1 ) {
+	public function renderChildren( Title $title, int $depth = 1 ): string {
 		if ( !$title->inNamespace( NS_CATEGORY ) ) {
 			// Non-categories can't have children. :)
 			return '';
@@ -274,10 +257,8 @@ class CategoryTree {
 
 	/**
 	 * Returns a string with an HTML representation of the parents of the given category.
-	 * @param Title $title
-	 * @return string
 	 */
-	public function renderParents( Title $title ) {
+	public function renderParents( Title $title ): string {
 		$dbr = $this->dbProvider->getReplicaDatabase();
 
 		$res = $dbr->newSelectQueryBuilder()
@@ -315,7 +296,7 @@ class CategoryTree {
 	 * @param int $children
 	 * @return string
 	 */
-	public function renderNode( Title $title, $children = 0 ) {
+	public function renderNode( Title $title, int $children = 0 ): string {
 		if ( $this->config->get( 'CategoryTreeUseCategoryTable' )
 			&& $title->inNamespace( NS_CATEGORY )
 			&& !$this->optionManager->isInverse()
@@ -331,12 +312,8 @@ class CategoryTree {
 	/**
 	 * Returns a string with a HTML represenation of the given page.
 	 * $info must be an associative array, containing at least a Title object under the 'title' key.
-	 * @param Title $title
-	 * @param Category|null $cat
-	 * @param int $children
-	 * @return string
 	 */
-	public function renderNodeInfo( Title $title, Category $cat = null, $children = 0 ) {
+	public function renderNodeInfo( Title $title, Category $cat = null, int $children = 0 ): string {
 		$mode = $this->optionManager->getOption( 'mode' );
 
 		$isInCatNS = $title->inNamespace( NS_CATEGORY );
@@ -458,14 +435,10 @@ class CategoryTree {
 
 	/**
 	 * Create a string which format the page, subcat and file counts of a category
-	 * @param IContextSource $context
-	 * @param ?Category $cat
-	 * @param int $countMode
-	 * @return string
 	 */
 	public static function createCountString( IContextSource $context, ?Category $cat,
-		$countMode
-	) {
+		int $countMode
+	): string {
 		$allCount = $cat ? $cat->getMemberCount() : 0;
 		$subcatCount = $cat ? $cat->getSubcatCount() : 0;
 		$fileCount = $cat ? $cat->getFileCount() : 0;
@@ -513,11 +486,9 @@ class CategoryTree {
 
 	/**
 	 * Creates a Title object from a user provided (and thus unsafe) string
-	 * @param string $title
-	 * @return null|Title
 	 */
-	public static function makeTitle( $title ) {
-		$title = trim( strval( $title ) );
+	public static function makeTitle( string $title ): ?Title {
+		$title = trim( $title );
 
 		if ( $title === '' ) {
 			return null;
diff --git a/includes/CategoryTreePage.php b/includes/CategoryTreePage.php
index 34f5abc1..b739a40c 100644
--- a/includes/CategoryTreePage.php
+++ b/includes/CategoryTreePage.php
@@ -36,22 +36,11 @@ use Wikimedia\Rdbms\IConnectionProvider;
  * to display the category structure of a wiki
  */
 class CategoryTreePage extends SpecialPage {
-	/** @var string */
-	public $target = '';
+	public string $target = '';
+	private IConnectionProvider $dbProvider;
+	private SearchEngineFactory $searchEngineFactory;
+	public ?CategoryTree $tree = null;
 
-	/** @var IConnectionProvider */
-	private $dbProvider;
-
-	/** @var SearchEngineFactory */
-	private $searchEngineFactory;
-
-	/** @var CategoryTree */
-	public $tree = null;
-
-	/**
-	 * @param IConnectionProvider $dbProvider
-	 * @param SearchEngineFactory $searchEngineFactory
-	 */
 	public function __construct(
 		IConnectionProvider $dbProvider,
 		SearchEngineFactory $searchEngineFactory
@@ -65,7 +54,7 @@ class CategoryTreePage extends SpecialPage {
 	 * @param string $name
 	 * @return mixed
 	 */
-	private function getOption( $name ) {
+	private function getOption( string $name ) {
 		if ( $this->tree ) {
 			return $this->tree->optionManager->getOption( $name );
 		} else {
diff --git a/includes/Hooks.php b/includes/Hooks.php
index 2f26b745..4a6a8adf 100644
--- a/includes/Hooks.php
+++ b/includes/Hooks.php
@@ -62,25 +62,11 @@ class Hooks implements
 	CategoryViewer__doCategoryQueryHook,
 	CategoryViewer__generateLinkHook
 {
-
-	/** @var CategoryCache */
-	private $categoryCache;
-
-	/** @var Config */
-	private $config;
-
-	/** @var IConnectionProvider */
+	private CategoryCache $categoryCache;
+	private Config $config;
 	private IConnectionProvider $dbProvider;
+	private LinkRenderer $linkRenderer;
 
-	/** @var LinkRenderer */
-	private $linkRenderer;
-
-	/**
-	 * @param CategoryCache $categoryCache
-	 * @param Config $config
-	 * @param IConnectionProvider $dbProvider
-	 * @param LinkRenderer $linkRenderer
-	 */
 	public function __construct(
 		CategoryCache $categoryCache,
 		Config $config,
@@ -215,10 +201,10 @@ class Hooks implements
 		$attr = Sanitizer::validateTagAttributes( $argv, 'div' );
 
 		$hideroot = isset( $argv['hideroot'] )
-			? OptionManager::decodeBoolean( $argv['hideroot'] ) : null;
+			? OptionManager::decodeBoolean( $argv['hideroot'] ) : false;
 		$onlyroot = isset( $argv['onlyroot'] )
-			? OptionManager::decodeBoolean( $argv['onlyroot'] ) : null;
-		$depthArg = isset( $argv['depth'] ) ? (int)$argv['depth'] : null;
+			? OptionManager::decodeBoolean( $argv['onlyroot'] ) : false;
+		$depthArg = isset( $argv['depth'] ) ? (int)$argv['depth'] : 1;
 
 		$depth = $ct->optionManager->capDepth( $depthArg );
 		if ( $onlyroot ) {
diff --git a/includes/OptionManager.php b/includes/OptionManager.php
index 2ac8285f..1bea88db 100644
--- a/includes/OptionManager.php
+++ b/includes/OptionManager.php
@@ -33,16 +33,9 @@ use MediaWiki\MediaWikiServices;
  * Core functions to handle the options
  */
 class OptionManager {
-	/** @var array */
-	private $mOptions = [];
+	private array $mOptions = [];
+	private Config $config;
 
-	/** @var Config */
-	private $config;
-
-	/**
-	 * @param array $options
-	 * @param Config $config
-	 */
 	public function __construct( array $options, Config $config ) {
 		$this->config = $config;
 
@@ -76,10 +69,7 @@ class OptionManager {
 		}
 	}
 
-	/**
-	 * @return array
-	 */
-	public function getOptions() {
+	public function getOptions(): array {
 		return $this->mOptions;
 	}
 
@@ -87,14 +77,11 @@ class OptionManager {
 	 * @param string $name
 	 * @return mixed
 	 */
-	public function getOption( $name ) {
+	public function getOption( string $name ) {
 		return $this->mOptions[$name];
 	}
 
-	/**
-	 * @return bool
-	 */
-	public function isInverse() {
+	public function isInverse(): bool {
 		return $this->getOption( 'mode' ) === CategoryTreeMode::PARENTS;
 	}
 
@@ -182,11 +169,11 @@ class OptionManager {
 	 * Helper function to convert a string to a boolean value.
 	 * Perhaps make this a global function in MediaWiki proper
 	 * @param mixed $value
-	 * @return bool|null|string
+	 * @return bool
 	 */
-	public static function decodeBoolean( $value ) {
+	public static function decodeBoolean( $value ): bool {
 		if ( $value === null ) {
-			return null;
+			return false;
 		}
 		if ( is_bool( $value ) ) {
 			return $value;
@@ -204,12 +191,6 @@ class OptionManager {
 			|| $value === 'true' || $value === 't' || $value === 'on'
 		) {
 			return true;
-		} elseif ( $value === 'no' || $value === 'n'
-			|| $value === 'false' || $value === 'f' || $value === 'off'
-		) {
-			return false;
-		} elseif ( $value === 'null' || $value === 'default' || $value === 'none' || $value === 'x' ) {
-			return null;
 		} else {
 			return false;
 		}
@@ -263,7 +244,7 @@ class OptionManager {
 	 * @param string $enc
 	 * @return mixed
 	 */
-	private static function encodeOptions( array $options, $enc ) {
+	private static function encodeOptions( array $options, string $enc ) {
 		if ( $enc === 'mode' || $enc === '' ) {
 			$opt = $options['mode'];
 		} elseif ( $enc === 'json' ) {
@@ -279,7 +260,7 @@ class OptionManager {
 	 * @param int|null $depth
 	 * @return string
 	 */
-	public function getOptionsAsCacheKey( $depth = null ) {
+	public function getOptionsAsCacheKey( int $depth = null ): string {
 		$key = '';
 
 		foreach ( $this->mOptions as $k => $v ) {
@@ -299,7 +280,7 @@ class OptionManager {
 	 * @param int|null $depth
 	 * @return mixed
 	 */
-	public function getOptionsAsJsStructure( $depth = null ) {
+	public function getOptionsAsJsStructure( int $depth = null ) {
 		$opt = $this->mOptions;
 		if ( $depth !== null ) {
 			$opt['depth'] = $depth;
@@ -311,15 +292,10 @@ class OptionManager {
 	/**
 	 * Internal function to cap depth
 	 * @param int $depth
-	 * @return int|mixed
+	 * @return int
 	 */
-	public function capDepth( $depth ) {
-		if ( !is_numeric( $depth ) ) {
-			return 1;
-		}
-
+	public function capDepth( int $depth ): int {
 		$mode = $this->getOption( 'mode' );
-		$depth = intval( $depth );
 		$maxDepth = $this->config->get( 'CategoryTreeMaxDepth' );
 
 		if ( is_array( $maxDepth ) ) {