Respect · henriquemoody · Jun 25, 2026 · Jun 24, 2026
diff --git a/docs/validators.md b/docs/validators.md
@@ -9,7 +9,7 @@ SPDX-FileContributor: Henrique Moody <henriquemoody@gmail.com>
 
 In this page you will find a list of validators by their category.
 
-**Arrays**: [ArrayType][] - [ArrayVal][] - [Contains][] - [ContainsAny][] - [ContainsCount][] - [Each][] - [EndsWith][] - [In][] - [Key][] - [KeyExists][] - [KeyOptional][] - [KeySet][] - [Sorted][] - [StartsWith][] - [Subset][] - [Unique][]
+**Arrays**: [ArrayType][] - [ArrayVal][] - [Contains][] - [ContainsAny][] - [ContainsCount][] - [Each][] - [EachKey][] - [EndsWith][] - [In][] - [Key][] - [KeyExists][] - [KeyOptional][] - [KeySet][] - [Sorted][] - [StartsWith][] - [Subset][] - [Unique][]
 
 **Banking**: [CreditCard][] - [Iban][]
 
@@ -43,7 +43,7 @@ In this page you will find a list of validators by their category.
 
 **Miscellaneous**: [Blank][] - [Falsy][] - [Named][] - [Templated][] - [Undef][]
 
-**Nesting**: [After][] - [AllOf][] - [AnyOf][] - [Each][] - [Factory][] - [Given][] - [Key][] - [KeySet][] - [NoneOf][] - [Not][] - [NullOr][] - [OneOf][] - [Property][] - [PropertyOptional][] - [ShortCircuit][] - [UndefOr][] - [When][]
+**Nesting**: [After][] - [AllOf][] - [AnyOf][] - [Each][] - [EachKey][] - [Factory][] - [Given][] - [Key][] - [KeySet][] - [NoneOf][] - [Not][] - [NullOr][] - [OneOf][] - [Property][] - [PropertyOptional][] - [ShortCircuit][] - [UndefOr][] - [When][]
 
 **Numbers**: [Base][] - [Decimal][] - [Digit][] - [Even][] - [Factor][] - [Finite][] - [FloatType][] - [FloatVal][] - [Infinite][] - [IntType][] - [IntVal][] - [Multiple][] - [Negative][] - [Number][] - [NumericVal][] - [Odd][] - [Positive][] - [Roman][]
 
@@ -100,6 +100,7 @@ In this page you will find a list of validators by their category.
 - [Directory][] - `v::directory()->assert(__DIR__);`
 - [Domain][] - `v::domain()->assert('google.com');`
 - [Each][] - `v::each(v::dateTime())->assert($releaseDates);`
+- [EachKey][] - `v::eachKey(v::stringType())->assert($releaseDates);`
 - [Email][] - `v::email()->assert('alganet@gmail.com');`
 - [Emoji][] - `v::emoji()->assert('🍕');`
 - [EndsWith][] - `v::endsWith('ipsum')->assert('lorem ipsum');`
@@ -259,6 +260,7 @@ In this page you will find a list of validators by their category.
 [Directory]: validators/Directory.md "Validates if the given path is a directory."
 [Domain]: validators/Domain.md "Validates whether the input is a valid domain name or not."
 [Each]: validators/Each.md "Validates whether each value in the input is valid according to another validator."
+[EachKey]: validators/EachKey.md "Validates whether each key in the input is valid according to another validator."
 [Email]: validators/Email.md "Validates an email address."
 [Emoji]: validators/Emoji.md "Validates if the input is an emoji or a sequence of emojis."
 [EndsWith]: validators/EndsWith.md "This validator is similar to `Contains()`, but validates"

diff --git a/docs/validators/Each.md b/docs/validators/Each.md
@@ -92,6 +92,7 @@ v::length(v::greaterThan(0))->each(v::equals(10))->assert([]);
 - [After](After.md)
 - [All](All.md)
 - [ArrayVal](ArrayVal.md)
+- [EachKey](EachKey.md)
 - [Falsy](Falsy.md)
 - [IterableType](IterableType.md)
 - [IterableVal](IterableVal.md)

diff --git a/docs/validators/EachKey.md b/docs/validators/EachKey.md
@@ -0,0 +1,111 @@
+<!--
+SPDX-License-Identifier: MIT
+SPDX-FileCopyrightText: (c) Respect Project Contributors
+SPDX-FileContributor: Henrique Moody <henriquemoody@gmail.com>
+-->
+
+# EachKey
+
+- `EachKey(Validator $validator)`
+
+Validates whether each key in the input is valid according to another validator.
+
+```php
+$releaseDates = [
+    'validation' => '2010-01-01',
+    'template'   => '2011-01-01',
+    'relational' => '2011-02-05',
+];
+
+v::eachKey(v::stringType())->assert($releaseDates);
+// Validation passes successfully
+```
+
+This validator is the key-type counterpart to [Each](Each.md). While `Each` validates
+values, `EachKey` validates keys. This allows composable validation of array key types:
+
+```php
+v::eachKey(v::stringType())->assert(['a' => 1, 'b' => 2]);
+// Validation passes successfully
+
+v::eachKey(v::stringType())->assert([0 => 'x', 1 => 'y']);
+// → - Each key of `["x", "y"]` must be valid
+// →   - Key `.0` must be a string
+// →   - Key `.1` must be a string
+```
+
+You can combine `EachKey` with [Each](Each.md) via [AllOf](AllOf.md) to validate both
+keys and values independently:
+
+```php
+v::allOf(v::eachKey(v::stringType()), v::each(v::intType()))->assert(['a' => 1, 'b' => 2]);
+// Validation passes successfully
+```
+
+## Note
+
+This validator will pass if the input is empty. Use [Length](Length.md) with [GreaterThan](GreaterThan.md) to perform a stricter check:
+
+```php
+v::eachKey(v::stringType())->assert([]);
+// Validation passes successfully
+
+v::length(v::greaterThan(0))->eachKey(v::stringType())->assert([]);
+// → The length of `[]` must be greater than 0
+```
+
+## Templates
+
+### `EachKey::TEMPLATE_STANDARD`
+
+|       Mode | Template                                |
+| ---------: | :-------------------------------------- |
+|  `default` | Each key of {{subject}} must be valid   |
+| `inverted` | Each key of {{subject}} must be invalid |
+
+### `EachKey::TEMPLATE_NESTED`
+
+|       Mode | Template |
+| ---------: | :------- |
+|  `default` | Key      |
+| `inverted` | Key      |
+
+### `EachKey::TEMPLATE_SHORT_CIRCUITED`
+
+|       Mode | Template    |
+| ---------: | :---------- |
+|  `default` | Each key of |
+| `inverted` | Each key of |
+
+## Template placeholders
+
+- **TEMPLATE_STANDARD**: Uses `{{subject}}` — the validated input or the custom
+  validator name (if specified).
+- **TEMPLATE_NESTED**: Does not use placeholders. Composes with the inner
+  validator's template via `asAdjacentOf` to produce messages like
+  "Key `.0` must be a string".
+
+## Categorization
+
+- Arrays
+- Nesting
+
+## Changelog
+
+| Version | Description |
+| ------: | :---------- |
+|   3.2.0 | Created     |
+
+## See Also
+
+- [After](After.md)
+- [All](All.md)
+- [AllOf](AllOf.md)
+- [Each](Each.md)
+- [IterableType](IterableType.md)
+- [IterableVal](IterableVal.md)
+- [Key](Key.md)
+- [KeyExists](KeyExists.md)
+- [KeyOptional](KeyOptional.md)
+- [KeySet](KeySet.md)
+- [Length](Length.md)
diff --git a/src/Mixins/AllBuilder.php b/src/Mixins/AllBuilder.php
diff --git a/src/Mixins/AllChain.php b/src/Mixins/AllChain.php
diff --git a/src/Mixins/Builder.php b/src/Mixins/Builder.php
diff --git a/src/Mixins/Chain.php b/src/Mixins/Chain.php
diff --git a/src/Mixins/KeyBuilder.php b/src/Mixins/KeyBuilder.php
diff --git a/src/Mixins/KeyChain.php b/src/Mixins/KeyChain.php
diff --git a/src/Mixins/NotBuilder.php b/src/Mixins/NotBuilder.php
diff --git a/src/Mixins/NotChain.php b/src/Mixins/NotChain.php
diff --git a/src/Mixins/NullOrBuilder.php b/src/Mixins/NullOrBuilder.php
diff --git a/src/Mixins/NullOrChain.php b/src/Mixins/NullOrChain.php
diff --git a/src/Mixins/PropertyBuilder.php b/src/Mixins/PropertyBuilder.php
diff --git a/src/Mixins/PropertyChain.php b/src/Mixins/PropertyChain.php
diff --git a/src/Mixins/UndefOrBuilder.php b/src/Mixins/UndefOrBuilder.php
diff --git a/src/Mixins/UndefOrChain.php b/src/Mixins/UndefOrChain.php
diff --git a/src/Validators/EachKey.php b/src/Validators/EachKey.php
@@ -0,0 +1,85 @@
+<?php
+
+/*
+ * SPDX-License-Identifier: MIT
+ * SPDX-FileCopyrightText: (c) Respect Project Contributors
+ * SPDX-FileContributor: Henrique Moody <henriquemoody@gmail.com>
+ */
+
+declare(strict_types=1);
+
+namespace Respect\Validation\Validators;
+
+use Attribute;
+use Respect\Validation\Helpers\CanEvaluateShortCircuit;
+use Respect\Validation\Message\Template;
+use Respect\Validation\Path;
+use Respect\Validation\Result;
+use Respect\Validation\Validators\Core\FilteredArray;
+use Respect\Validation\Validators\Core\ShortCircuitable;
+
+use function array_keys;
+use function array_reduce;
+
+#[Attribute(Attribute::TARGET_PROPERTY | Attribute::IS_REPEATABLE)]
+#[Template(
+    'Each key of {{subject}} must be valid',
+    'Each key of {{subject}} must be invalid',
+    self::TEMPLATE_STANDARD,
+)]
+#[Template('Key', 'Key', self::TEMPLATE_NESTED)]
+#[Template('Each key of', 'Each key of', self::TEMPLATE_SHORT_CIRCUITED)]
+final class EachKey extends FilteredArray implements ShortCircuitable
+{
+    use CanEvaluateShortCircuit;
+
+    public const string TEMPLATE_NESTED = '__nested__';
+    public const string TEMPLATE_SHORT_CIRCUITED = '__short_circuited__';
+
+    public function evaluateShortCircuit(mixed $input): Result
+    {
+        $iterableResult = (new IterableType())->evaluate($input);
+        if (!$iterableResult->hasPassed) {
+            return $iterableResult->withIdFrom($this);
+        }
+
+        $result = null;
+        // phpcs:ignore SlevomatCodingStandard.Variables.UnusedVariable.UnusedVariable -- only keys are validated
+        foreach ($input as $key => $value) {
+            $result = $this->evaluateShortCircuitWith($this->validator, $key);
+            if (!$result->hasPassed) {
+                return $result->asAdjacentOf(
+                    Result::failed($key, $this, [], self::TEMPLATE_NESTED),
+                    'eachKey',
+                )->withPath(new Path($key));
+            }
+        }
+
+        if ($result === null) {
+            return Result::passed($input, $this)->asIndeterminate();
+        }
+
+        return $result->asAdjacentOf(Result::passed($input, $this, [], self::TEMPLATE_SHORT_CIRCUITED), 'eachKey');
+    }
+
+    /** @param non-empty-array<mixed> $input */
+    protected function evaluateArray(array $input): Result
+    {
+        $children = [];
+        foreach (array_keys($input) as $key) {
+            $validatorResult = $this->validator->evaluate($key);
+            $children[] = $validatorResult->asAdjacentOf(
+                Result::of($validatorResult->hasPassed, $key, $this, [], self::TEMPLATE_NESTED),
+                'eachKey',
+            )->withPath(new Path($key));
+        }
+
+        $hasPassed = array_reduce(
+            $children,
+            static fn($carry, $childResult) => $carry && $childResult->hasPassed,
+            true,
+        );
+
+        return Result::of($hasPassed, $input, $this)->withChildren(...$children);
+    }
+}