diff --git a/system/Common.php b/system/Common.php
index 37c661d69261..75db2ce1da9d 100644
--- a/system/Common.php
+++ b/system/Common.php
@@ -768,14 +768,14 @@ function lang(string $line, array $args = [], ?string $locale = null)
             $language->setLocale($locale);
         }
 
-        $line = $language->getLine($line, $args);
+        $lines = $language->getLine($line, $args);
 
         if ($locale && $locale !== $activeLocale) {
             // Reset to active locale
             $language->setLocale($activeLocale);
         }
 
-        return $line;
+        return $lines;
     }
 }
 
diff --git a/system/Language/en/Validation.php b/system/Language/en/Validation.php
index c78099de38f6..2a980ba4c5a6 100644
--- a/system/Language/en/Validation.php
+++ b/system/Language/en/Validation.php
@@ -29,6 +29,7 @@
     'differs'               => 'The {field} field must differ from the {param} field.',
     'equals'                => 'The {field} field must be exactly: {param}.',
     'exact_length'          => 'The {field} field must be exactly {param} characters in length.',
+    'field_exists'          => 'The {field} field must exist.',
     'greater_than'          => 'The {field} field must contain a number greater than {param}.',
     'greater_than_equal_to' => 'The {field} field must contain a number greater than or equal to {param}.',
     'hex'                   => 'The {field} field may only contain hexadecimal characters.',
diff --git a/system/Validation/Rules.php b/system/Validation/Rules.php
index 0af02b802904..0af5be8166f0 100644
--- a/system/Validation/Rules.php
+++ b/system/Validation/Rules.php
@@ -11,6 +11,7 @@
 
 namespace CodeIgniter\Validation;
 
+use CodeIgniter\Helpers\Array\ArrayHelper;
 use Config\Database;
 use InvalidArgumentException;
 
@@ -427,4 +428,26 @@ public function required_without(
 
         return true;
     }
+
+    /**
+     * The field exists in $data.
+     *
+     * @param array|bool|float|int|object|string|null $value The field value.
+     * @param string|null                             $param The rule's parameter.
+     * @param array                                   $data  The data to be validated.
+     * @param string|null                             $field The field name.
+     */
+    public function field_exists(
+        $value = null,
+        ?string $param = null,
+        array $data = [],
+        ?string $error = null,
+        ?string $field = null
+    ): bool {
+        if (strpos($field, '.') !== false) {
+            return ArrayHelper::dotKeyExists($field, $data);
+        }
+
+        return array_key_exists($field, $data);
+    }
 }
diff --git a/system/Validation/StrictRules/Rules.php b/system/Validation/StrictRules/Rules.php
index 70d081975a62..bf671c3bec4f 100644
--- a/system/Validation/StrictRules/Rules.php
+++ b/system/Validation/StrictRules/Rules.php
@@ -13,6 +13,7 @@
 
 namespace CodeIgniter\Validation\StrictRules;
 
+use CodeIgniter\Helpers\Array\ArrayHelper;
 use CodeIgniter\Validation\Rules as NonStrictRules;
 use Config\Database;
 
@@ -403,4 +404,26 @@ public function required_without(
     ): bool {
         return $this->nonStrictRules->required_without($str, $otherFields, $data, $error, $field);
     }
+
+    /**
+     * The field exists in $data.
+     *
+     * @param array|bool|float|int|object|string|null $value The field value.
+     * @param string|null                             $param The rule's parameter.
+     * @param array                                   $data  The data to be validated.
+     * @param string|null                             $field The field name.
+     */
+    public function field_exists(
+        $value = null,
+        ?string $param = null,
+        array $data = [],
+        ?string $error = null,
+        ?string $field = null
+    ): bool {
+        if (strpos($field, '.') !== false) {
+            return ArrayHelper::dotKeyExists($field, $data);
+        }
+
+        return array_key_exists($field, $data);
+    }
 }
diff --git a/system/Validation/Validation.php b/system/Validation/Validation.php
index 747ac66d9bc4..5dbf4b7f5d93 100644
--- a/system/Validation/Validation.php
+++ b/system/Validation/Validation.php
@@ -184,7 +184,7 @@ public function run(?array $data = null, ?string $group = null, ?string $dbGroup
 
             if ($values === []) {
                 // We'll process the values right away if an empty array
-                $this->processRules($field, $setup['label'] ?? $field, $values, $rules, $data);
+                $this->processRules($field, $setup['label'] ?? $field, $values, $rules, $data, $field);
 
                 continue;
             }
@@ -196,7 +196,7 @@ public function run(?array $data = null, ?string $group = null, ?string $dbGroup
                 }
             } else {
                 // Process single field
-                $this->processRules($field, $setup['label'] ?? $field, $values, $rules, $data);
+                $this->processRules($field, $setup['label'] ?? $field, $values, $rules, $data, $field);
             }
         }
 
@@ -323,10 +323,15 @@ protected function processRules(
                         continue;
                     }
 
-                    $found  = true;
-                    $passed = $param === false
-                        ? $set->{$rule}($value, $error)
-                        : $set->{$rule}($value, $param, $data, $error, $field);
+                    $found = true;
+
+                    if ($rule === 'field_exists') {
+                        $passed = $set->{$rule}($value, $param, $data, $error, $originalField);
+                    } else {
+                        $passed = ($param === false)
+                            ? $set->{$rule}($value, $error)
+                            : $set->{$rule}($value, $param, $data, $error, $field);
+                    }
 
                     break;
                 }
@@ -351,8 +356,10 @@ protected function processRules(
 
                 $param = ($param === false) ? '' : $param;
 
+                $fieldForErrors = ($rule === 'field_exists') ? $originalField : $field;
+
                 // @phpstan-ignore-next-line $error may be set by rule methods.
-                $this->errors[$field] = $error ?? $this->getErrorMessage(
+                $this->errors[$fieldForErrors] = $error ?? $this->getErrorMessage(
                     ($this->isClosure($rule) || $arrayCallable) ? (string) $i : $rule,
                     $field,
                     $label,
diff --git a/tests/system/Validation/RulesTest.php b/tests/system/Validation/RulesTest.php
index ac2f34bf825a..4844d898e3a9 100644
--- a/tests/system/Validation/RulesTest.php
+++ b/tests/system/Validation/RulesTest.php
@@ -47,6 +47,7 @@ class RulesTest extends CIUnitTestCase
     protected function setUp(): void
     {
         parent::setUp();
+
         $this->validation = new Validation((object) $this->config, Services::renderer());
         $this->validation->reset();
     }
@@ -63,6 +64,7 @@ public function testRequired(array $data, bool $expected): void
     public static function provideRequired(): iterable
     {
         yield from [
+            [[], false],
             [['foo' => null], false],
             [['foo' => 123], true],
             [['foo' => null, 'bar' => 123], false],
@@ -138,6 +140,11 @@ public static function providePermitEmpty(): iterable
     {
         yield from [
             // If the rule is only `permit_empty`, any value will pass.
+            [
+                ['foo' => 'permit_empty|valid_email'],
+                [],
+                true,
+            ],
             [
                 ['foo' => 'permit_empty|valid_email'],
                 ['foo' => ''],
@@ -203,8 +210,8 @@ public static function providePermitEmpty(): iterable
                 ['foo' => 'invalid'],
                 false,
             ],
-            // Required has more priority
             [
+                // Required has more priority
                 ['foo' => 'permit_empty|required|valid_email'],
                 ['foo' => ''],
                 false,
@@ -224,8 +231,8 @@ public static function providePermitEmpty(): iterable
                 ['foo' => false],
                 false,
             ],
-            // This tests will return true because the input data is trimmed
             [
+                // This tests will return true because the input data is trimmed
                 ['foo' => 'permit_empty|required'],
                 ['foo' => '0'],
                 true,
@@ -280,8 +287,8 @@ public static function providePermitEmpty(): iterable
                 ['foo' => '', 'bar' => 1],
                 true,
             ],
-            // Testing with closure
             [
+                // Testing with closure
                 ['foo' => ['permit_empty', static fn ($value) => true]],
                 ['foo' => ''],
                 true,
@@ -845,4 +852,104 @@ public static function provideRequiredWithoutMultipleWithoutFields(): iterable
             ],
         ];
     }
+
+    /**
+     * @dataProvider provideFieldExists
+     */
+    public function testFieldExists(array $rules, array $data, bool $expected): void
+    {
+        $this->validation->setRules($rules);
+        $this->assertSame($expected, $this->validation->run($data));
+    }
+
+    public static function provideFieldExists(): iterable
+    {
+        // Do not use `foo`, because there is a lang file `Foo`, and
+        // the error message may be messed up.
+        yield from [
+            'empty string' => [
+                ['fiz' => 'field_exists'],
+                ['fiz' => ''],
+                true,
+            ],
+            'null' => [
+                ['fiz' => 'field_exists'],
+                ['fiz' => null],
+                true,
+            ],
+            'false' => [
+                ['fiz' => 'field_exists'],
+                ['fiz' => false],
+                true,
+            ],
+            'empty array' => [
+                ['fiz' => 'field_exists'],
+                ['fiz' => []],
+                true,
+            ],
+            'empty data' => [
+                ['fiz' => 'field_exists'],
+                [],
+                false,
+            ],
+            'dot array syntax: true' => [
+                ['fiz.bar' => 'field_exists'],
+                [
+                    'fiz' => ['bar' => null],
+                ],
+                true,
+            ],
+            'dot array syntax: false' => [
+                ['fiz.bar' => 'field_exists'],
+                [],
+                false,
+            ],
+            'dot array syntax asterisk: true' => [
+                ['fiz.*.baz' => 'field_exists'],
+                [
+                    'fiz' => [
+                        'bar' => [
+                            'baz' => null,
+                        ],
+                    ],
+                ],
+                true,
+            ],
+            'dot array syntax asterisk: false' => [
+                ['fiz.*.baz' => 'field_exists'],
+                [
+                    'fiz' => [
+                        'bar' => [
+                            'baz' => null,
+                        ],
+                        'hoge' => [
+                            // 'baz' is missing.
+                        ],
+                    ],
+                ],
+                false,
+            ],
+        ];
+    }
+
+    public function testFieldExistsErrorMessage(): void
+    {
+        $this->validation->setRules(['fiz.*.baz' => 'field_exists']);
+        $data = [
+            'fiz' => [
+                'bar' => [
+                    'baz' => null,
+                ],
+                'hoge' => [
+                    // 'baz' is missing.
+                ],
+            ],
+        ];
+
+        $this->assertFalse($this->validation->run($data));
+        $this->assertSame(
+            ['fiz.*.baz' => 'The fiz.*.baz field must exist.'],
+            $this->validation->getErrors()
+        );
+    }
 }
diff --git a/tests/system/Validation/StrictRules/RulesTest.php b/tests/system/Validation/StrictRules/RulesTest.php
index 74ed4d6cecd6..6c9bcd470176 100644
--- a/tests/system/Validation/StrictRules/RulesTest.php
+++ b/tests/system/Validation/StrictRules/RulesTest.php
@@ -53,6 +53,11 @@ public function testPermitEmptyStrict(array $rules, array $data, bool $expected)
     public static function providePermitEmptyStrict(): iterable
     {
         yield from [
+            [
+                ['foo' => 'permit_empty'],
+                [],
+                true,
+            ],
             [
                 ['foo' => 'permit_empty'],
                 ['foo' => ''],
diff --git a/user_guide_src/source/changelogs/v4.5.0.rst b/user_guide_src/source/changelogs/v4.5.0.rst
index f2440ac5cc92..06434719b093 100644
--- a/user_guide_src/source/changelogs/v4.5.0.rst
+++ b/user_guide_src/source/changelogs/v4.5.0.rst
@@ -226,6 +226,9 @@ Model
 Libraries
 =========
 
+- **Validation:** Added the new rule ``field_exists`` that checks the filed
+  exists in the data to be validated.
+
 Helpers and Functions
 =====================
 
@@ -244,6 +247,8 @@ Others
 Message Changes
 ***************
 
+- Added ``Validation.field_exists`` error message.
+
 Changes
 *******
 
diff --git a/user_guide_src/source/libraries/validation.rst b/user_guide_src/source/libraries/validation.rst
index b415a4e0fea7..dc76c34723c1 100644
--- a/user_guide_src/source/libraries/validation.rst
+++ b/user_guide_src/source/libraries/validation.rst
@@ -271,6 +271,21 @@ for including multiple Rulesets, and collections of rules that can be easily reu
 .. note:: You may never need to use this method, as both the :doc:`Controller </incoming/controllers>` and
     the :doc:`Model </models/model>` provide methods to make validation even easier.
 
+********************
+How Validation Works
+********************
+
+- The validation never changes data to be validated.
+- The validation checks each field in turn according to the Validation Rules you
+  set. If any rule returns false, the check for that field ends there.
+- The Format Rules do not permit empty string. If you want to permit empty string,
+  add the ``permit_empty`` rule.
+- If a field does not exist in the data to be validated, the value is interpreted
+  as ``null``. If you want to check that the field exists, add the ``field_exists``
+  rule.
+
+.. note:: The ``field_exists`` rule can be used since v4.5.0.
+
 ************************
 Setting Validation Rules
 ************************
@@ -894,6 +909,8 @@ differs                 Yes        Fails if field does not differ from the one
                                    in the parameter.
 exact_length            Yes        Fails if field is not exactly the parameter   ``exact_length[5]`` or ``exact_length[5,8,12]``
                                    value. One or more comma-separated values.
+field_exists            Yes        Fails if field does not exist. (This rule was
+                                   added in v4.5.0.)
 greater_than            Yes        Fails if field is less than or equal to       ``greater_than[8]``
                                    the parameter value or not numeric.
 greater_than_equal_to   Yes        Fails if field is less than the parameter     ``greater_than_equal_to[5]``