diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 814ab29..6b22e2e 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: ['7.3', '7.4', '8.0', '8.1']
+        php: ['7.4', '8.0', '8.1']
         stability: [ prefer-lowest, prefer-stable ]
 
     name: PHP ${{ matrix.php }} - ${{ matrix.stability }} tests
diff --git a/composer.json b/composer.json
index 5e1e670..1853c3d 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php" : "^7.3 || ^8.0"
+        "php" : "^7.4 || ^8.0"
     },
     "require-dev": {
         "phpunit/phpunit" : "^8.5.21 || ^9.5"
diff --git a/src/CronExpression.php b/src/CronExpression.php
index 61c79f6..f129e11 100644
--- a/src/CronExpression.php
+++ b/src/CronExpression.php
@@ -4,32 +4,15 @@
 
 class CronExpression
 {
-    /** @var string */
-    public $raw;
-
-    /** @var MinutesField */
-    public $minute;
-
-    /** @var HoursField */
-    public $hour;
-
-    /** @var DaysOfMonthField */
-    public $day;
-
-    /** @var MonthsField */
-    public $month;
-
-    /** @var DaysOfWeekField */
-    public $weekday;
-
-    /** @var string */
-    public $locale;
-
-    /** @var bool */
-    public $timeFormat24hours;
-
-    /** @var array */
-    public $translations;
+    public string $raw;
+    public MinutesField $minute;
+    public HoursField $hour;
+    public DaysOfMonthField $day;
+    public MonthsField $month;
+    public DaysOfWeekField $weekday;
+    public string $locale;
+    public bool $timeFormat24hours;
+    public array $translations;
 
     public function __construct(string $cron, string $locale = 'en', bool $timeFormat24hours = false)
     {
@@ -61,9 +44,7 @@ public function langCountable(string $type, int $number)
     {
         $array = $this->translations[$type];
 
-        $value = isset($array[$number])
-            ? $array[$number]
-            : ($array['default'] ?: '');
+        $value = $array[$number] ?? ($array['default'] ?: '');
 
         return str_replace(':number', $number, $value);
     }
@@ -86,6 +67,9 @@ protected function ensureLocaleExists(string $fallbackLocale = 'en')
         }
     }
 
+    /**
+     * @throws TranslationFileMissingException
+     */
     protected function loadTranslations()
     {
         $this->translations = [
diff --git a/src/CronTranslator.php b/src/CronTranslator.php
index 01bbb22..c1ff48b 100644
--- a/src/CronTranslator.php
+++ b/src/CronTranslator.php
@@ -6,7 +6,7 @@
 
 class CronTranslator
 {
-    private static $extendedMap = [
+    private static array $extendedMap = [
         '@yearly' => '0 0 1 1 *',
         '@annually' => '0 0 1 1 *',
         '@monthly' => '0 0 1 * *',
@@ -67,7 +67,7 @@ protected static function orderFields(array $fields)
         );
     }
 
-    protected static function filterType(array $fields, ...$types)
+    protected static function filterType(array $fields, ...$types): array
     {
         return array_filter($fields, function (Field $field) use ($types) {
             return $field->hasType(...$types);
diff --git a/src/CronType.php b/src/CronType.php
index 5250de5..3c4629b 100644
--- a/src/CronType.php
+++ b/src/CronType.php
@@ -8,17 +8,10 @@ class CronType
         'Every', 'Increment', 'Multiple', 'Once',
     ];
 
-    /** @var string */
-    public $type;
-
-    /** @var ?int */
-    public $value;
-
-    /** @var ?int */
-    public $count;
-
-    /** @var ?int */
-    public $increment;
+    public string $type;
+    public ?int $value;
+    public ?int $count;
+    public ?int $increment;
 
     private function __construct(string $type, ?int $value = null, ?int $count = null, ?int $increment = null)
     {
@@ -48,6 +41,9 @@ public static function once(int $value): CronType
         return new static('Once', $value);
     }
 
+    /**
+     * @throws CronParsingException
+     */
     public static function parse(string $expression): CronType
     {
         // Parse "*".
diff --git a/src/DaysOfMonthField.php b/src/DaysOfMonthField.php
index 5461cef..16143f2 100644
--- a/src/DaysOfMonthField.php
+++ b/src/DaysOfMonthField.php
@@ -4,7 +4,7 @@
 
 class DaysOfMonthField extends Field
 {
-    public $position = 2;
+    public int $position = 2;
 
     public function translateEvery()
     {
@@ -38,16 +38,16 @@ public function translateMultiple()
         ]);
     }
 
-    public function translateOnce()
+    public function translateOnce(): ?string
     {
         $month = $this->expression->month;
 
         if ($month->hasType('Once')) {
-            return; // MonthsField adapts to "On January the 1st".
+            return null; // MonthsField adapts to "On January the 1st".
         }
 
         if ($month->hasType('Every') && ! $month->dropped) {
-            return; // MonthsField adapts to "The 1st of every month".
+            return null; // MonthsField adapts to "The 1st of every month".
         }
 
         if ($month->hasType('Every') && $month->dropped) {
diff --git a/src/DaysOfWeekField.php b/src/DaysOfWeekField.php
index 7ed1ecf..60a615a 100644
--- a/src/DaysOfWeekField.php
+++ b/src/DaysOfWeekField.php
@@ -4,7 +4,7 @@
 
 class DaysOfWeekField extends Field
 {
-    public $position = 4;
+    public int $position = 4;
 
     public function translateEvery()
     {
@@ -43,7 +43,7 @@ public function translateOnce()
         ]);
     }
 
-    public function format()
+    public function format(): string
     {
         $weekday = $this->getValue() === 0 ? 7 : $this->getValue();
 
diff --git a/src/Field.php b/src/Field.php
index 0fdfb68..83470b4 100644
--- a/src/Field.php
+++ b/src/Field.php
@@ -4,20 +4,11 @@
 
 abstract class Field
 {
-    /** @var CronExpression */
-    public $expression;
-
-    /** @var string */
-    public $rawField;
-
-    /** @var CronType */
-    public $type;
-
-    /** @var bool */
-    public $dropped = false;
-
-    /** @var int */
-    public $position;
+    public CronExpression $expression;
+    public string $rawField;
+    public CronType $type;
+    public bool $dropped = false;
+    public int $position;
 
     public function __construct(CronExpression $expression, string $rawField)
     {
diff --git a/src/HoursField.php b/src/HoursField.php
index 3757837..7bb91c3 100644
--- a/src/HoursField.php
+++ b/src/HoursField.php
@@ -4,7 +4,7 @@
 
 class HoursField extends Field
 {
-    public $position = 1;
+    public int $position = 1;
 
     public function translateEvery()
     {
diff --git a/src/MinutesField.php b/src/MinutesField.php
index 0e58747..926efb1 100644
--- a/src/MinutesField.php
+++ b/src/MinutesField.php
@@ -4,7 +4,7 @@
 
 class MinutesField extends Field
 {
-    public $position = 0;
+    public int $position = 0;
 
     public function translateEvery()
     {
diff --git a/src/MonthsField.php b/src/MonthsField.php
index ab2343a..71b54a2 100644
--- a/src/MonthsField.php
+++ b/src/MonthsField.php
@@ -4,7 +4,7 @@
 
 class MonthsField extends Field
 {
-    public $position = 3;
+    public int $position = 3;
 
     public function translateEvery()
     {
@@ -52,6 +52,9 @@ public function translateOnce()
         ]);
     }
 
+    /**
+     * @throws CronParsingException
+     */
     public function format()
     {
         if ($this->getValue() < 1 || $this->getValue() > 12) {