diff --git a/.github/workflows/coding-standards.yml b/.github/workflows/coding-standards.yml
index cda56180f..357279bdf 100644
--- a/.github/workflows/coding-standards.yml
+++ b/.github/workflows/coding-standards.yml
@@ -11,7 +11,10 @@ on:
 jobs:
   coding-standards:
     uses: alleyinteractive/.github/.github/workflows/php-coding-standards.yml@main
+    with:
+      php: 8.1
   code-quality:
     uses: alleyinteractive/.github/.github/workflows/php-code-quality.yml@main
     with:
       command: "validate-monorepo"
+      php: 8.1
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index ad4056f02..9f4d00270 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -12,7 +12,7 @@ jobs:
   php-tests:
     strategy:
       matrix:
-        php: [8.0]
+        php: [8.0, 8.1]
         wordpress: ["latest"]
         multisite: [true, false]
     uses: alleyinteractive/.github/.github/workflows/php-tests.yml@main
diff --git a/composer.json b/composer.json
index a26786f8f..935009eeb 100644
--- a/composer.json
+++ b/composer.json
@@ -39,7 +39,8 @@
         "symfony/string": "^6.0",
         "symfony/var-dumper": "^6.0",
         "vlucas/phpdotenv": "^5.5",
-        "voku/portable-ascii": "^2.0"
+        "voku/portable-ascii": "^2.0",
+        "wp-coding-standards/wpcs": "dev-php-8-1 as 2.3.x-dev"
     },
     "require-dev": {
         "alleyinteractive/alley-coding-standards": "^1.0",
@@ -128,6 +129,12 @@
         ],
         "validate-monorepo": "monorepo-builder validate --ansi"
     },
+    "repositories": [
+        {
+            "type": "vcs",
+            "url": "https://github.com/alleyinteractive/WordPress-Coding-Standards"
+        }
+    ],
     "minimum-stability": "dev",
     "prefer-stable": true
 }
diff --git a/src/mantle/database/model/class-model.php b/src/mantle/database/model/class-model.php
index e33493923..95f656adc 100644
--- a/src/mantle/database/model/class-model.php
+++ b/src/mantle/database/model/class-model.php
@@ -573,7 +573,7 @@ public function to_array(): array {
 	 *
 	 * @return array
 	 */
-	public function jsonSerialize() {
+	public function jsonSerialize(): mixed {
 		return $this->to_array();
 	}
 
diff --git a/src/mantle/database/pagination/class-paginator.php b/src/mantle/database/pagination/class-paginator.php
index 8a7635182..71470925c 100644
--- a/src/mantle/database/pagination/class-paginator.php
+++ b/src/mantle/database/pagination/class-paginator.php
@@ -483,7 +483,7 @@ public function to_array(): array {
 	 *
 	 * @return array
 	 */
-	public function jsonSerialize() {
+	public function jsonSerialize(): mixed {
 		return $this->to_array();
 	}
 
@@ -503,7 +503,7 @@ public function to_json( $options = 0 ) {
 	 * @param mixed $offset Array offset.
 	 * @return bool
 	 */
-	public function offsetExists( $offset ): bool {
+	public function offsetExists( mixed $offset ): bool {
 		return isset( $this->items[ $offset ] );
 	}
 
@@ -513,7 +513,7 @@ public function offsetExists( $offset ): bool {
 	 * @param mixed $offset Offset to get.
 	 * @return mixed
 	 */
-	public function offsetGet( $offset ) {
+	public function offsetGet( mixed $offset ): mixed {
 		return $this->items[ $offset ];
 	}
 
@@ -524,7 +524,7 @@ public function offsetGet( $offset ) {
 	 * @param mixed $value  Value to set.
 	 * @return void
 	 */
-	public function offsetSet( $offset, $value ): void {
+	public function offsetSet( mixed $offset, mixed $value ): void {
 		$this->items[ $offset ] = $value;
 	}
 
diff --git a/src/mantle/http/class-request.php b/src/mantle/http/class-request.php
index 5e27bc167..5a536e3cc 100644
--- a/src/mantle/http/class-request.php
+++ b/src/mantle/http/class-request.php
@@ -466,10 +466,10 @@ public function offsetExists( mixed $offset ): bool {
 	/**
 	 * Get the value at the given offset.
 	 *
-	 * @param  string $offset
+	 * @param  mixed $offset
 	 * @return mixed
 	 */
-	public function offsetGet( $offset ) {
+	public function offsetGet( mixed $offset ): mixed {
 		return $this->__get( $offset );
 	}
 
diff --git a/src/mantle/support/class-collection.php b/src/mantle/support/class-collection.php
index 7bbbcc1e3..1d3e87b16 100644
--- a/src/mantle/support/class-collection.php
+++ b/src/mantle/support/class-collection.php
@@ -595,10 +595,10 @@ public function implode( $value, $glue = null ) {
 		$first = $this->first();
 
 		if ( is_array( $first ) || is_object( $first ) ) {
-			return implode( $glue, $this->pluck( $value )->all() );
+			return implode( $glue ?? '', $this->pluck( $value )->all() );
 		}
 
-		return implode( $value, $this->items );
+		return implode( $value ?? '', $this->items );
 	}
 
 	/**
diff --git a/src/mantle/support/class-str.php b/src/mantle/support/class-str.php
index 987f03b7c..5cbd5bc6e 100644
--- a/src/mantle/support/class-str.php
+++ b/src/mantle/support/class-str.php
@@ -229,7 +229,7 @@ public static function contains( $haystack, $needles ) {
 	 */
 	public static function ends_with( $haystack, $needles ) {
 		foreach ( (array) $needles as $needle ) {
-			if ( substr( $haystack, - strlen( $needle ) ) === (string) $needle ) {
+			if ( '' !== (string) $needle && str_ends_with( $haystack, (string) $needle ) ) {
 				return true;
 			}
 		}
diff --git a/src/mantle/support/traits/trait-enumerates-values.php b/src/mantle/support/traits/trait-enumerates-values.php
index 72b38933b..703f8cfe3 100644
--- a/src/mantle/support/traits/trait-enumerates-values.php
+++ b/src/mantle/support/traits/trait-enumerates-values.php
@@ -756,7 +756,7 @@ function ( $value ) {
 	 *
 	 * @return array<TKey, TValue>
 	 */
-	public function jsonSerialize() { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.MethodNameInvalid
+	public function jsonSerialize(): mixed { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.MethodNameInvalid
 		return array_map(
 			function ( $value ) {
 				if ( $value instanceof JsonSerializable ) {
diff --git a/tests/helpers/test-helpers-array.php b/tests/helpers/test-helpers-array.php
index e68fd9103..9cefe50fa 100644
--- a/tests/helpers/test-helpers-array.php
+++ b/tests/helpers/test-helpers-array.php
@@ -323,29 +323,29 @@ public function testDataSetWithDoubleStar() {
 
 class SupportTestArrayAccess implements ArrayAccess
 {
-	protected $attributes = [];
+	protected array $attributes = [];
 
-	public function __construct($attributes = [])
+	public function __construct(array $attributes = [])
 	{
 		$this->attributes = $attributes;
 	}
 
-	public function offsetExists($offset)
+	public function offsetExists(mixed $offset): bool
 	{
 		return array_key_exists($offset, $this->attributes);
 	}
 
-	public function offsetGet($offset)
+	public function offsetGet(mixed $offset): mixed
 	{
 		return $this->attributes[$offset];
 	}
 
-	public function offsetSet($offset, $value)
+	public function offsetSet(mixed $offset, mixed $value): void
 	{
 		$this->attributes[$offset] = $value;
 	}
 
-	public function offsetUnset($offset)
+	public function offsetUnset(mixed $offset): void
 	{
 		unset($this->attributes[$offset]);
 	}
diff --git a/tests/support/test-collection.php b/tests/support/test-collection.php
index 12e00485a..66d4c0aa4 100644
--- a/tests/support/test-collection.php
+++ b/tests/support/test-collection.php
@@ -4406,22 +4406,22 @@ public function __construct($arr)
 		$this->arr = $arr;
 	}
 
-	public function offsetExists($offset)
+	public function offsetExists(mixed $offset): bool
 	{
 		return isset($this->arr[$offset]);
 	}
 
-	public function offsetGet($offset)
+	public function offsetGet(mixed $offset): mixed
 	{
 		return $this->arr[$offset];
 	}
 
-	public function offsetSet($offset, $value)
+	public function offsetSet(mixed $offset, mixed $value): void
 	{
 		$this->arr[$offset] = $value;
 	}
 
-	public function offsetUnset($offset)
+	public function offsetUnset(mixed $offset): void
 	{
 		unset($this->arr[$offset]);
 	}
@@ -4442,14 +4442,14 @@ public function to_json($options = 0)
 }
 
 class TestJsonSerializeObject implements JsonSerializable {
-	public function jsonSerialize()
+	public function jsonSerialize(): mixed
 	{
 		return ['foo' => 'bar'];
 	}
 }
 
 class TestJsonSerializeWithScalarValueObject implements JsonSerializable {
-	public function jsonSerialize()
+	public function jsonSerialize(): mixed
 	{
 		return 'foo';
 	}