diff --git a/includes/Request/DerivativeRequest.php b/includes/Request/DerivativeRequest.php
index 741935b02ec..fe3c173ff43 100644
--- a/includes/Request/DerivativeRequest.php
+++ b/includes/Request/DerivativeRequest.php
@@ -38,7 +38,7 @@ use MediaWiki\Session\Session;
  * @since 1.19
  */
 class DerivativeRequest extends FauxRequest {
-	private $base;
+	private WebRequest $base;
 	private $ip;
 
 	/**
diff --git a/includes/Rest/BasicAccess/BasicRequestAuthorizer.php b/includes/Rest/BasicAccess/BasicRequestAuthorizer.php
index 2c977324b82..7c77bf23b0a 100644
--- a/includes/Rest/BasicAccess/BasicRequestAuthorizer.php
+++ b/includes/Rest/BasicAccess/BasicRequestAuthorizer.php
@@ -13,8 +13,8 @@ use MediaWiki\Rest\RequestInterface;
  * @internal
  */
 abstract class BasicRequestAuthorizer {
-	protected $request;
-	protected $handler;
+	protected RequestInterface $request;
+	protected Handler $handler;
 
 	/**
 	 * @param RequestInterface $request
diff --git a/includes/Settings/Source/ArraySource.php b/includes/Settings/Source/ArraySource.php
index be7c66bdae3..e945e283229 100644
--- a/includes/Settings/Source/ArraySource.php
+++ b/includes/Settings/Source/ArraySource.php
@@ -10,7 +10,7 @@ use Stringable;
  * @since 1.38
  */
 class ArraySource implements Stringable, SettingsSource {
-	private $settings;
+	private array $settings;
 
 	public function __construct( array $settings ) {
 		$this->settings = $settings;
diff --git a/includes/api/ApiResult.php b/includes/api/ApiResult.php
index 95625ce0d8c..145f23c09a6 100644
--- a/includes/api/ApiResult.php
+++ b/includes/api/ApiResult.php
@@ -147,7 +147,7 @@ class ApiResult implements ApiSerializable {
 	private int $size;
 	/** @var int|false */
 	private $maxSize;
-	private $errorFormatter;
+	private ApiErrorFormatter $errorFormatter;
 
 	/**
 	 * @param int|false $maxSize Maximum result "size", or false for no limit
diff --git a/includes/libs/ReplacementArray.php b/includes/libs/ReplacementArray.php
index eb51b54061e..107ac4ed058 100644
--- a/includes/libs/ReplacementArray.php
+++ b/includes/libs/ReplacementArray.php
@@ -24,7 +24,7 @@ namespace MediaWiki\Language;
  * Wrapper around strtr() that holds replacements
  */
 class ReplacementArray {
-	private $data;
+	private array $data;
 
 	/**
 	 * Create an object with the specified replacement array
diff --git a/includes/libs/iterators/IteratorDecorator.php b/includes/libs/iterators/IteratorDecorator.php
index 28dfdbd2a5f..d97da4fd8ab 100644
--- a/includes/libs/iterators/IteratorDecorator.php
+++ b/includes/libs/iterators/IteratorDecorator.php
@@ -23,7 +23,7 @@
  * @ingroup Maintenance
  */
 abstract class IteratorDecorator implements Iterator {
-	protected $iterator;
+	protected Iterator $iterator;
 
 	/**
 	 * @stable to call
diff --git a/includes/libs/rdbms/dbal/DoctrineAbstractSchemaTrait.php b/includes/libs/rdbms/dbal/DoctrineAbstractSchemaTrait.php
index 025156fbabf..0f06ee2f467 100644
--- a/includes/libs/rdbms/dbal/DoctrineAbstractSchemaTrait.php
+++ b/includes/libs/rdbms/dbal/DoctrineAbstractSchemaTrait.php
@@ -19,6 +19,7 @@
  */
 namespace Wikimedia\Rdbms;
 
+use Doctrine\DBAL\Platforms\AbstractPlatform;
 use Doctrine\DBAL\Schema\Schema;
 
 /**
@@ -28,7 +29,7 @@ use Doctrine\DBAL\Schema\Schema;
  */
 trait DoctrineAbstractSchemaTrait {
 
-	private $platform;
+	private AbstractPlatform $platform;
 
 	private function addTableToSchema( Schema $schema, array $schemaSpec ) {
 		$prefix = $this->platform->getName() === 'postgresql' ? '' : '/*_*/';
diff --git a/includes/libs/rdbms/dbal/DoctrineSchemaBuilder.php b/includes/libs/rdbms/dbal/DoctrineSchemaBuilder.php
index dea028b8986..76c3488e7d4 100644
--- a/includes/libs/rdbms/dbal/DoctrineSchemaBuilder.php
+++ b/includes/libs/rdbms/dbal/DoctrineSchemaBuilder.php
@@ -12,8 +12,8 @@ use Doctrine\DBAL\Schema\Schema;
 class DoctrineSchemaBuilder implements SchemaBuilder {
 	use DoctrineAbstractSchemaTrait;
 
-	private $schema;
-	private $platform;
+	private Schema $schema;
+	private AbstractPlatform $platform;
 
 	/**
 	 * A builder object that take abstract schema definition and produces sql to create the tables.
diff --git a/includes/libs/rdbms/dbal/DoctrineSchemaChangeBuilder.php b/includes/libs/rdbms/dbal/DoctrineSchemaChangeBuilder.php
index 220435b785a..f76b78cff9e 100644
--- a/includes/libs/rdbms/dbal/DoctrineSchemaChangeBuilder.php
+++ b/includes/libs/rdbms/dbal/DoctrineSchemaChangeBuilder.php
@@ -13,7 +13,7 @@ use Doctrine\DBAL\Schema\Schema;
 class DoctrineSchemaChangeBuilder implements SchemaChangeBuilder {
 	use DoctrineAbstractSchemaTrait;
 
-	private $platform;
+	private AbstractPlatform $platform;
 
 	/**
 	 * A builder object that take abstract schema definition and produces sql to create the tables.
diff --git a/includes/parser/StripState.php b/includes/parser/StripState.php
index ac6cc81cd6f..7922795f7a7 100644
--- a/includes/parser/StripState.php
+++ b/includes/parser/StripState.php
@@ -32,7 +32,7 @@ class StripState {
 	protected $data;
 	protected $regex;
 
-	protected $parser;
+	protected ?Parser $parser;
 
 	protected $circularRefGuard;
 	protected $depth = 0;
diff --git a/includes/recentchanges/RCFeed/FormattedRCFeed.php b/includes/recentchanges/RCFeed/FormattedRCFeed.php
index c8996c3a399..9743c40225e 100644
--- a/includes/recentchanges/RCFeed/FormattedRCFeed.php
+++ b/includes/recentchanges/RCFeed/FormattedRCFeed.php
@@ -33,7 +33,7 @@ use RecentChange;
  * @ingroup RecentChanges
  */
 abstract class FormattedRCFeed extends RCFeed {
-	private $params;
+	private array $params;
 
 	/**
 	 * @param array $params