diff --git a/logic/Validator.php b/logic/Validator.php
index 30e878b..ece801d 100644
--- a/logic/Validator.php
+++ b/logic/Validator.php
@@ -1,15 +1,35 @@
 <?php
 namespace AirQuality;
 
+/**
+ * Makes validating user input easy.
+ */
 class Validator {
+	/**
+	 * The data that we test against.
+	 * @var array
+	 */
 	private $target_data;
+	/**
+	 * An array of tests that we should run against the above target data.
+	 * @var callable[]
+	 */
 	private $tests = [];
 	
+	/**
+	 * Creates a new validator instance.
+	 * @param array $in_target_data The target data to test against.
+	 */
 	public function __construct($in_target_data) {
 		$this->target_data = $in_target_data;
 	}
 	
-	public function exists($key) {
+	/**
+	 * Checks that the given key exists.
+	 * @param  string $key The key that should exist.
+	 * @return void
+	 */
+	public function exists(string $key) {
 		$this->add_test(
 			$key,
 			function($data) { return isset($data); },
@@ -18,7 +38,12 @@ class Validator {
 		);
 	}
 	
-	public function is_numberish($key) {
+	/**
+	 * Ensures that the value associated with the specified key is a number.
+	 * @param	string	$key	The key to check the value of.
+	 * @return	void
+	 */
+	public function is_numberish(string $key) {
 		$this->add_test(
 			$key,
 			function($data) { return is_numeric($data); },
@@ -26,7 +51,15 @@ class Validator {
 			"Error: The field $key in your request isn't a number."
 		);
 	}
-	public function is_min_length($key, $min_length) {
+	/**
+	 * Checks that the value associated with the given key is a least a given 
+	 * number of characters long.
+	 * This test is unicode aware.
+	 * @param	string	$key		The key to check the value of.
+	 * @param	int		$min_length	The minimum length required.
+	 * @return	void
+	 */
+	public function is_min_length(string $key, int $min_length) {
 		$this->add_test(
 			$key,
 			function($data) use ($min_length) { return mb_strlen($data) >= $min_length; },
@@ -34,7 +67,15 @@ class Validator {
 			"Error: The field $key is too short - it must be a minimum of $min_length characters."
 		);
 	}
-	public function is_max_length($key, $max_length) {
+	/**
+	 * Checks that the value associated with the given key is at most a given 
+	 * number of characters long.
+	 * This test is unicode aware.
+	 * @param	string	$key		The key to check the value of.
+	 * @param	int		$max_length	The maximum length allowed.
+	 * @return	void
+	 */
+	public function is_max_length(string $key, int $max_length) {
 		$this->add_test(
 			$key,
 			function($data) use ($max_length) { return mb_strlen($data) <= $max_length; },
@@ -42,6 +83,13 @@ class Validator {
 			"Error: The field $key is too long - it must be a maximum of $max_length characters."
 		);
 	}
+	/**
+	 * Ensures that the value associated with the given key is one of a 
+	 * predefined set of values.
+	 * @param string $key        The key to check the associated value of.
+	 * @param array  $values     The array of values to test against.
+	 * @param int    $error_code The HTTP response code to return if the test fails.
+	 */
 	public function is_preset_value(string $key, array $values, int $error_code) {
 		$this->add_test(
 			$key,
@@ -53,6 +101,13 @@ class Validator {
 		);
 	}
 	
+	/**
+	 * Ensures that 2 keys have the same value.
+	 * @param	string	$key_a		The first key.
+	 * @param	string	$key_b		The second key.
+	 * @param	string	$message	The message to return if the test fails.
+	 * @return	void
+	 */
 	public function are_equal($key_a, $key_b, $message) {
 		$key_b_data = $this->target_data[$key_b];
 		$this->add_test(
@@ -65,6 +120,14 @@ class Validator {
 		);
 	}
 	
+	/**
+	 * Ensures the value attached to a given key matches the specified regular 
+	 * expression.
+	 * @param  string $key     The key to check the value of.
+	 * @param  string $regex   The regular expression to test the value with.
+	 * @param  string $message Thee message to return if the test fails.
+	 * @return void
+	 */
 	public function matches_regex($key, $regex, $message) {
 		$this->add_test(
 			$key,
@@ -76,7 +139,11 @@ class Validator {
 		);
 	}
 
-	
+	/**
+	 * Ensures the value associated with the specified key is a valid datetime.
+	 * @param  string  $key The key of the value to check.
+	 * @return void
+	 */
 	public function is_datetime($key) {
 		$this->add_test(
 			$key,
@@ -88,7 +155,16 @@ class Validator {
 		);
 	}
 	
-	public function add_test($key, $test, $response_code, $message) {
+	/**
+	 * Add a custom test directly.
+	 * It's suggested that you don't call this directly - insteaad edit this
+	 * class' code to allow everyone to benefit from the improvement :-)
+	 * @param	string		$key			The key to test the value of.
+ 	 * @param	callable	$test			The test to run.
+	 * @param	int			$response_code	The HTTP response code to return if the test fails.
+	 * @param	string		$message		The message to send if the test fails.
+	 */
+	public function add_test(string $key, callable $test, int $response_code, string $message) {
 		$new_test = [
 			"key" => $key,
 			"test" => $test,
@@ -99,12 +175,23 @@ class Validator {
 		$this->tests[] = $new_test;
 	}
 	
-	protected function send_error($code, $message) {
+	/**
+	 * Sends an error to the client and then exits.
+	 * Don't put code after calling this method - it won't get executed!
+	 * @param	int		$code		The HTTP response code to send.
+ 	 * @param	string	$message	The plain-text message to send.
+	 */
+	protected function send_error(int $code, string $message) {
 		http_response_code($code);
 		header("content-type: text/plain");
 		exit($message);
 	}
 	
+	/**
+	 * Runs all the tests added to the validator so far.
+	 * Note that this won't return if a test fails.
+	 * @return	void
+	 */
 	public function run() {
 		foreach($this->tests as $test) {