diff --git a/src/Core/Config/Cache/ConfigCache.php b/src/Core/Config/Cache/ConfigCache.php
index b8175452b..3119b5db1 100644
--- a/src/Core/Config/Cache/ConfigCache.php
+++ b/src/Core/Config/Cache/ConfigCache.php
@@ -25,7 +25,7 @@ class ConfigCache
 	 * @param array $config             A initial config array
 	 * @param bool  $hidePasswordOutput True, if cache variables should take extra care of password values
 	 */
-	public function __construct(array $config = [], $hidePasswordOutput = true)
+	public function __construct(array $config = [], bool $hidePasswordOutput = true)
 	{
 		$this->hidePasswordOutput = $hidePasswordOutput;
 		$this->load($config);
@@ -38,7 +38,7 @@ class ConfigCache
 	 * @param array $config
 	 * @param bool  $overwrite Force value overwrite if the config key already exists
 	 */
-	public function load(array $config, $overwrite = false)
+	public function load(array $config, bool $overwrite = false)
 	{
 		$categories = array_keys($config);
 
@@ -68,7 +68,7 @@ class ConfigCache
 	 *
 	 * @return null|mixed Returns the value of the Config entry or null if not set
 	 */
-	public function get($cat, $key = null)
+	public function get(string $cat, string $key = null)
 	{
 		if (isset($this->config[$cat][$key])) {
 			return $this->config[$cat][$key];
@@ -82,14 +82,14 @@ class ConfigCache
 	/**
 	 * Sets a default value in the config cache. Ignores already existing keys.
 	 *
-	 * @param string $cat Config category
-	 * @param string $k   Config key
-	 * @param mixed  $v   Default value to set
+	 * @param string $cat   Config category
+	 * @param string $key   Config key
+	 * @param mixed  $value Default value to set
 	 */
-	private function setDefault($cat, $k, $v)
+	private function setDefault(string $cat, string $key, $value)
 	{
-		if (!isset($this->config[$cat][$k])) {
-			$this->set($cat, $k, $v);
+		if (!isset($this->config[$cat][$key])) {
+			$this->set($cat, $key, $value);
 		}
 	}
 
@@ -102,7 +102,7 @@ class ConfigCache
 	 *
 	 * @return bool True, if the value is set
 	 */
-	public function set($cat, $key, $value)
+	public function set(string $cat, string $key, $value)
 	{
 		if (!isset($this->config[$cat])) {
 			$this->config[$cat] = [];
@@ -111,7 +111,7 @@ class ConfigCache
 		if ($this->hidePasswordOutput &&
 		    $key == 'password' &&
 		    is_string($value)) {
-			$this->config[$cat][$key] = new HiddenString((string) $value);
+			$this->config[$cat][$key] = new HiddenString((string)$value);
 		} else {
 			$this->config[$cat][$key] = $value;
 		}
@@ -126,7 +126,7 @@ class ConfigCache
 	 *
 	 * @return bool true, if deleted
 	 */
-	public function delete($cat, $key)
+	public function delete(string $cat, string $key)
 	{
 		if (isset($this->config[$cat][$key])) {
 			unset($this->config[$cat][$key]);
diff --git a/src/Core/Config/Cache/PConfigCache.php b/src/Core/Config/Cache/PConfigCache.php
index 98adfa2ce..4ee2bfae7 100644
--- a/src/Core/Config/Cache/PConfigCache.php
+++ b/src/Core/Config/Cache/PConfigCache.php
@@ -20,9 +20,9 @@ class PConfigCache
 	private $hidePasswordOutput;
 
 	/**
-	 * @param bool  $hidePasswordOutput True, if cache variables should take extra care of password values
+	 * @param bool $hidePasswordOutput True, if cache variables should take extra care of password values
 	 */
-	public function __construct($hidePasswordOutput = true)
+	public function __construct(bool $hidePasswordOutput = true)
 	{
 		$this->hidePasswordOutput = $hidePasswordOutput;
 	}
@@ -34,7 +34,7 @@ class PConfigCache
 	 * @param int   $uid
 	 * @param array $config
 	 */
-	public function load($uid, array $config)
+	public function load(int $uid, array $config)
 	{
 		$categories = array_keys($config);
 
@@ -56,13 +56,13 @@ class PConfigCache
 	/**
 	 * Retrieves a value from the user config cache
 	 *
-	 * @param int    $uid     User Id
-	 * @param string $cat     Config category
-	 * @param string $key     Config key
+	 * @param int    $uid User Id
+	 * @param string $cat Config category
+	 * @param string $key Config key
 	 *
 	 * @return null|string The value of the config entry or null if not set
 	 */
-	public function get($uid, $cat, $key = null)
+	public function get(int $uid, string $cat, $key = null)
 	{
 		if (isset($this->config[$uid][$cat][$key])) {
 			return $this->config[$uid][$cat][$key];
@@ -85,7 +85,7 @@ class PConfigCache
 	 *
 	 * @return bool Set successful
 	 */
-	public function set($uid, $cat, $key, $value)
+	public function set(int $uid, string $cat, string $key, $value)
 	{
 		if (!isset($this->config[$uid]) || !is_array($this->config[$uid])) {
 			$this->config[$uid] = [];
@@ -98,7 +98,7 @@ class PConfigCache
 		if ($this->hidePasswordOutput &&
 		    $key == 'password' &&
 		    !empty($value) && is_string($value)) {
-			$this->config[$uid][$cat][$key] = new HiddenString((string) $value);
+			$this->config[$uid][$cat][$key] = new HiddenString((string)$value);
 		} else {
 			$this->config[$uid][$cat][$key] = $value;
 		}
@@ -116,7 +116,7 @@ class PConfigCache
 	 *
 	 * @return bool true, if deleted
 	 */
-	public function delete($uid, $cat, $key)
+	public function delete(int $uid, string $cat, string $key)
 	{
 		if (isset($this->config[$uid][$cat][$key])) {
 			unset($this->config[$uid][$cat][$key]);
diff --git a/src/Core/Config/Configuration.php b/src/Core/Config/Configuration.php
index 759120f55..37b947d11 100644
--- a/src/Core/Config/Configuration.php
+++ b/src/Core/Config/Configuration.php
@@ -42,8 +42,59 @@ abstract class Configuration
 		return $this->configCache;
 	}
 
+	/**
+	 * @brief Loads all configuration values of family into a cached storage.
+	 *
+	 * All configuration values of the system are stored in the cache ( @see IConfigCache )
+	 *
+	 * @param string $cat The category of the configuration value
+	 *
+	 * @return void
+	 */
 	abstract public function load(string $cat = 'config');
+
+	/**
+	 * @brief Get a particular user's config variable given the category name
+	 * ($cat) and a $key.
+	 *
+	 * Get a particular config value from the given category ($cat)
+	 * and the $key from a cached storage either from the $this->configAdapter
+	 * (@see IConfigAdapter ) or from the $this->configCache (@see IConfigCache ).
+	 *
+	 * @param string  $cat        The category of the configuration value
+	 * @param string  $key           The configuration key to query
+	 * @param mixed   $default_value optional, The value to return if key is not set (default: null)
+	 * @param boolean $refresh       optional, If true the config is loaded from the db and not from the cache (default: false)
+	 *
+	 * @return mixed Stored value or null if it does not exist
+	 */
 	abstract public function get(string $cat, string $key, $default_value = null, bool $refresh = false);
+
+	/**
+	 * @brief Sets a configuration value for system config
+	 *
+	 * Stores a config value ($value) in the category ($cat) under the key ($key)
+	 *
+	 * Note: Please do not store booleans - convert to 0/1 integer values!
+	 *
+	 * @param string $cat The category of the configuration value
+	 * @param string $key    The configuration key to set
+	 * @param mixed  $value  The value to store
+	 *
+	 * @return bool Operation success
+	 */
 	abstract public function set(string $cat, string $key, $value);
+
+	/**
+	 * @brief Deletes the given key from the system configuration.
+	 *
+	 * Removes the configured value from the stored cache in $this->configCache
+	 * (@see ConfigCache ) and removes it from the database (@see IConfigAdapter ).
+	 *
+	 * @param string $cat The category of the configuration value
+	 * @param string $key    The configuration key to delete
+	 *
+	 * @return bool
+	 */
 	abstract public function delete(string $cat, string $key);
 }