diff --git a/src/BaseCollection.php b/src/BaseCollection.php
index 0bf46f0dc..f6fa9bbd4 100644
--- a/src/BaseCollection.php
+++ b/src/BaseCollection.php
@@ -70,9 +70,11 @@ class BaseCollection extends \ArrayIterator
 	}
 
 	/**
-	 * @return int
+	 * Getter for total count
+	 *
+	 * @return int Total count
 	 */
-	public function getTotalCount()
+	public function getTotalCount(): int
 	{
 		return $this->totalCount;
 	}
@@ -85,7 +87,7 @@ class BaseCollection extends \ArrayIterator
 	 * @return array
 	 * @see array_column()
 	 */
-	public function column($column, $index_key = null)
+	public function column(string $column, $index_key = null): array
 	{
 		return array_column($this->getArrayCopy(true), $column, $index_key);
 	}
@@ -97,7 +99,7 @@ class BaseCollection extends \ArrayIterator
 	 * @return BaseCollection
 	 * @see array_map()
 	 */
-	public function map(callable $callback)
+	public function map(callable $callback): BaseCollection
 	{
 		return new static(array_map($callback, $this->getArrayCopy()), $this->getTotalCount());
 	}
@@ -110,7 +112,7 @@ class BaseCollection extends \ArrayIterator
 	 * @return BaseCollection
 	 * @see array_filter()
 	 */
-	public function filter(callable $callback = null, int $flag = 0)
+	public function filter(callable $callback = null, int $flag = 0): BaseCollection
 	{
 		return new static(array_filter($this->getArrayCopy(), $callback, $flag));
 	}
diff --git a/src/BaseEntity.php b/src/BaseEntity.php
index 8e8938feb..065d100fa 100644
--- a/src/BaseEntity.php
+++ b/src/BaseEntity.php
@@ -55,14 +55,14 @@ abstract class BaseEntity extends BaseDataTransferObject
 	}
 
 	/**
-	 * @param $name
+	 * @param mixed $name
 	 * @return bool
 	 * @throws HTTPException\InternalServerErrorException
 	 */
-	public function __isset($name)
+	public function __isset($name): bool
 	{
 		if (!property_exists($this, $name)) {
-			throw new HTTPException\InternalServerErrorException('Unknown property ' . $name . ' in Entity ' . static::class);
+			throw new HTTPException\InternalServerErrorException('Unknown property ' . $name . ' of type ' . gettype($name) . ' in Entity ' . static::class);
 		}
 
 		return !empty($this->$name);
diff --git a/src/BaseModel.php b/src/BaseModel.php
index 768e9e9e5..06a61c505 100644
--- a/src/BaseModel.php
+++ b/src/BaseModel.php
@@ -110,11 +110,11 @@ abstract class BaseModel extends BaseDataTransferObject
 	 * - $model->field (outside of class)
 	 * - $this->field (inside of class)
 	 *
-	 * @param $name
+	 * @param string $name Name of data to fetch
 	 * @return mixed
 	 * @throws HTTPException\InternalServerErrorException
 	 */
-	public function __get($name)
+	public function __get(string $name)
 	{
 		$this->checkValid();
 
diff --git a/src/BaseModule.php b/src/BaseModule.php
index c03a77e29..f70662a62 100644
--- a/src/BaseModule.php
+++ b/src/BaseModule.php
@@ -331,7 +331,7 @@ abstract class BaseModule implements ICanHandleRequests
 	 *    Actually, important actions should not be triggered by Links / GET-Requests at all, but sometimes they still are,
 	 *    so this mechanism brings in some damage control (the attacker would be able to forge a request to a form of this type, but not to forms of other types).
 	 */
-	public static function getFormSecurityToken($typename = '')
+	public static function getFormSecurityToken(string $typename = '')
 	{
 		$user      = User::getById(DI::app()->getLoggedInUserId(), ['guid', 'prvkey']);
 		$timestamp = time();
@@ -340,7 +340,14 @@ abstract class BaseModule implements ICanHandleRequests
 		return $timestamp . '.' . $sec_hash;
 	}
 
-	public static function checkFormSecurityToken($typename = '', $formname = 'form_security_token')
+	/**
+	 * Checks if form's security (CSRF) token is valid.
+	 *
+	 * @param string $typename ???
+	 * @param string $formname Name of form/field (???)
+	 * @return bool Whether it is valid
+	 */
+	public static function checkFormSecurityToken(string $typename = '', string $formname = 'form_security_token'): bool
 	{
 		$hash = null;
 
@@ -372,12 +379,12 @@ abstract class BaseModule implements ICanHandleRequests
 		return ($sec_hash == $x[1]);
 	}
 
-	public static function getFormSecurityStandardErrorMessage()
+	public static function getFormSecurityStandardErrorMessage(): string
 	{
 		return DI::l10n()->t("The form security token was not correct. This probably happened because the form has been opened for too long \x28>3 hours\x29 before submitting it.") . EOL;
 	}
 
-	public static function checkFormSecurityTokenRedirectOnError($err_redirect, $typename = '', $formname = 'form_security_token')
+	public static function checkFormSecurityTokenRedirectOnError(string $err_redirect, string $typename = '', string $formname = 'form_security_token')
 	{
 		if (!self::checkFormSecurityToken($typename, $formname)) {
 			Logger::notice('checkFormSecurityToken failed: user ' . DI::app()->getLoggedInUserNickname() . ' - form element ' . $typename);
@@ -387,7 +394,7 @@ abstract class BaseModule implements ICanHandleRequests
 		}
 	}
 
-	public static function checkFormSecurityTokenForbiddenOnError($typename = '', $formname = 'form_security_token')
+	public static function checkFormSecurityTokenForbiddenOnError(string $typename = '', string $formname = 'form_security_token')
 	{
 		if (!self::checkFormSecurityToken($typename, $formname)) {
 			Logger::notice('checkFormSecurityToken failed: user ' . DI::app()->getLoggedInUserNickname() . ' - form element ' . $typename);
diff --git a/src/LegacyModule.php b/src/LegacyModule.php
index 22d393ef9..7d9cf2028 100644
--- a/src/LegacyModule.php
+++ b/src/LegacyModule.php
@@ -57,7 +57,7 @@ class LegacyModule extends BaseModule
 	 * @param string $file_path
 	 * @throws \Exception
 	 */
-	private function setModuleFile($file_path)
+	private function setModuleFile(string $file_path)
 	{
 		if (!is_readable($file_path)) {
 			throw new \Exception(DI::l10n()->t('Legacy module file not found: %s', $file_path));
@@ -87,7 +87,7 @@ class LegacyModule extends BaseModule
 	 * @return string
 	 * @throws \Exception
 	 */
-	private function runModuleFunction(string $function_suffix)
+	private function runModuleFunction(string $function_suffix): string
 	{
 		$function_name = $this->moduleName . '_' . $function_suffix;