diff --git a/Annotations/AnnotationGenerator.php b/Annotations/AnnotationGenerator.php
index 84c85c5..3024a45 100644
--- a/Annotations/AnnotationGenerator.php
+++ b/Annotations/AnnotationGenerator.php
@@ -437,15 +437,25 @@ public function buildParameterAnnotationData(string $methodName, string $paramNa
         if (count($typeHints) > 1 && in_array('bool', $typeHints)) {
             $typeHints = array_diff($typeHints, ['bool']);
         }
-        foreach ($typeHints as $typePart) {
-            $typePart = trim($typePart, ' ()');
-            $normalisedType = $this->getOpenApiTypeFromPhpType($typePart);
-            // If the type is array, check if there's a subType
-            $subType = null;
-            if ($normalisedType === 'array' && $typePart !== 'array' && strpos($typePart, '[]') !== false) {
-                $subType = substr($typePart, 0, strpos($typePart, '[]'));
+
+        $allTypeHintsAreStringLiterals = $this->areAllTypeHintsStringLiterals($typeHints);
+        $enumValues = [];
+        if ($allTypeHintsAreStringLiterals) {
+            $typesMap['string'] = null;
+            foreach ($typeHints as $typeHint) {
+                $enumValues[] = trim(trim($typeHint), '\'"');
+            }
+        } else {
+            foreach ($typeHints as $typePart) {
+                $typePart = trim($typePart, ' ()');
+                $normalisedType = $this->getOpenApiTypeFromPhpType($typePart);
+                // If the type is array, check if there's a subType
+                $subType = null;
+                if ($normalisedType === 'array' && $typePart !== 'array' && strpos($typePart, '[]') !== false) {
+                    $subType = substr($typePart, 0, strpos($typePart, '[]'));
+                }
+                $typesMap[$normalisedType] = $subType !== null ? $this->getOpenApiTypeFromPhpType($subType) : $subType;
             }
-            $typesMap[$normalisedType] = $subType !== null ? $this->getOpenApiTypeFromPhpType($subType) : $subType;
         }
 
         $isRequired = !key_exists('default', $paramMetadata) || $paramMetadata['default'] instanceof NoDefaultValue;
@@ -474,7 +484,7 @@ public function buildParameterAnnotationData(string $methodName, string $paramNa
             $default = json_encode($default);
         }
 
-        return [
+        $paramData = [
             'name' => $paramName,
             'types' => $typesMap,
             'description' => $description,
@@ -482,6 +492,37 @@ public function buildParameterAnnotationData(string $methodName, string $paramNa
             'default' => !$isRequired ? $default : NoDefaultValue::class,
             'example' => $example,
         ];
+
+        if (!empty($enumValues)) {
+            $paramData['enum'] = $enumValues;
+        }
+
+        return $paramData;
+    }
+
+    /**
+     * Determine whether all type hints are quoted string literals.
+     *
+     * @param array $typeHints
+     *
+     * @return bool
+     */
+    protected function areAllTypeHintsStringLiterals(array $typeHints): bool
+    {
+        if (empty($typeHints)) {
+            return false;
+        }
+
+        foreach ($typeHints as $typeHint) {
+            $typeHint = trim(strval($typeHint));
+            $firstChar = $typeHint[0] ?? '';
+            $lastChar = $typeHint[strlen($typeHint) - 1] ?? '';
+            if (!(($firstChar === "'" && $lastChar === "'") || ($firstChar === '"' && $lastChar === '"'))) {
+                return false;
+            }
+        }
+
+        return true;
     }
 
     /**
@@ -1715,12 +1756,19 @@ public function buildLinesForAnnotationObject(string $objectName, array $objectP
      * @param string $subType This can specify the subtype for arrays. E.g. integer for int[] or string for string[].
      * @param string $default The optional default value for the type. Default is no value.
      * @param string $example The optional example value for the type. Default is empty string which indicated no value.
+     * @param array $enum The optional enum values for the type.
      *
      * @return array[]
      */
-    public function buildSchemaObjectArray(string $type, string $subType = '', string $default = NoDefaultValue::class, string $example = ''): array
+    public function buildSchemaObjectArray(string $type, string $subType = '', string $default = NoDefaultValue::class, string $example = '', array $enum = []): array
     {
         $schemaMap = ['type="' . $type . '"'];
+        if (!empty($enum) && $type === 'string') {
+            $enumStringValues = array_map(static function ($value) {
+                return '"' . str_replace('"', '\"', strval($value)) . '"';
+            }, $enum);
+            $schemaMap[] = 'enum={' . implode(',', $enumStringValues) . '}';
+        }
         if (($example) !== '') {
             $schemaMap[] = 'example=' . $this->wrapStringWithQuotes($example, $type);
         }
@@ -1800,14 +1848,16 @@ public function shouldIncludeDefault(string $type, string $default = NoDefaultVa
      * default is set.
      * @param string $example The value to use as the example property of the schema. If it's an empty string, no
      * example is set.
+     * @param array $enum The optional enum values to apply to string schemas.
      *
      * @return array[] The collection of lines which make up the schema annotation object.
      */
-    public function buildSchemaObjectArrays(array $typesMap, string $default = '', string $example = ''): array
+    public function buildSchemaObjectArrays(array $typesMap, string $default = '', string $example = '', array $enum = []): array
     {
         $schemas = [];
         foreach ($typesMap as $type => $subType) {
-            $schemas[] = $this->buildSchemaObjectArray($type, $subType ?? '', $default, $example);
+            $schemaEnum = $type === 'string' ? $enum : [];
+            $schemas[] = $this->buildSchemaObjectArray($type, $subType ?? '', $default, $example, $schemaEnum);
         }
 
         if (count($schemas) === 1) {
@@ -1867,7 +1917,12 @@ public function compileOperationLines(string $path, string $opId, string $plugin
                 // Escape quotes differently for the annotation examples
                 $exampleString = str_replace('\"', '""', $exampleString);
             }
-            $paramMap[] = $this->buildSchemaObjectArrays($param['types'], strval($param['default']), strval($exampleString));
+            $paramMap[] = $this->buildSchemaObjectArrays(
+                $param['types'],
+                strval($param['default']),
+                strval($exampleString),
+                $param['enum'] ?? []
+            );
             $operationValuesMap[] = ['@OA\Parameter' => $paramMap];
         }
         foreach ($responses as $response) {
diff --git a/CHANGELOG.md b/CHANGELOG.md
index cf8b2a2..895de6f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
 ## Changelog
 
+5.0.2-b1 - 2026-02-16
+- Added support for string literal union types
 
 5.0.1-b1 - 2026-02-16
 - Added class and function level docs
diff --git a/plugin.json b/plugin.json
index 71c1c66..76e6c4a 100644
--- a/plugin.json
+++ b/plugin.json
@@ -1,7 +1,7 @@
 {
     "name": "OpenApiDocs",
     "description": "Generate API documentation for Matomo in the OpenAPI format.",
-    "version": "5.0.1-b1",
+    "version": "5.0.2-b1",
     "theme": false,
     "keywords": [
         "API",
@@ -28,4 +28,4 @@
         "source": "https:\/\/github.com\/matomo-org\/plugin-OpenApiDocs"
     },
     "category": "development"
-}
\ No newline at end of file
+}
diff --git a/tests/Unit/AnnotationGeneratorTest.php b/tests/Unit/AnnotationGeneratorTest.php
index 5f34842..9790de7 100644
--- a/tests/Unit/AnnotationGeneratorTest.php
+++ b/tests/Unit/AnnotationGeneratorTest.php
@@ -596,6 +596,38 @@ public function getTestDataForBuildParameterAnnotationData(): iterable
             'default' => 'Piwik\API\NoDefaultValue',
             'example' => '',
         ]];
+        yield 'should extract enum values when docInfo is a union of string literals' => ['period', [], [
+            'type' => "'day'|'week'|'month'",
+        ], [
+            'name' => 'period',
+            'types' => ['string' => null],
+            'description' => '',
+            'required' => 'true',
+            'default' => 'Piwik\API\NoDefaultValue',
+            'example' => '',
+            'enum' => ['day', 'week', 'month'],
+        ]];
+        yield 'should extract enum values when docInfo uses double-quoted string literals' => ['format', [], [
+            'type' => '"json"|"xml"',
+        ], [
+            'name' => 'format',
+            'types' => ['string' => null],
+            'description' => '',
+            'required' => 'true',
+            'default' => 'Piwik\API\NoDefaultValue',
+            'example' => '',
+            'enum' => ['json', 'xml'],
+        ]];
+        yield 'should not add enum when union mixes string literal and non-literal type' => ['period', [], [
+            'type' => "'day'|int",
+        ], [
+            'name' => 'period',
+            'types' => ['string' => null, 'integer' => null],
+            'description' => '',
+            'required' => 'true',
+            'default' => 'Piwik\API\NoDefaultValue',
+            'example' => '',
+        ]];
         yield 'should allow multiple types when metadata type is string' => ['someParam', [
             'type' => 'string',
         ], [
@@ -1081,10 +1113,27 @@ public function testBuildLinesForAnnotationObject(): void
         $this->expectNotToPerformAssertions();
     }
 
-    public function testBuildSchemaObjectArray(): void
+    public function testBuildSchemaObjectArrayWithStringEnum(): void
     {
-        // TODO - buildSchemaObjectArray method
-        $this->expectNotToPerformAssertions();
+        $expectedWithEnum = [
+            '@OA\Schema' => [
+                'type="string"',
+                'enum={"day","week"}',
+                'example="day"',
+            ],
+        ];
+        $this->assertEquals($expectedWithEnum, $this->annotationGenerator->buildSchemaObjectArray('string', '', NoDefaultValue::class, 'day', ['day', 'week']));
+    }
+
+    public function testBuildSchemaObjectArrayIgnoresEnumForNonStringTypes(): void
+    {
+        $expectedWithoutEnum = [
+            '@OA\Schema' => [
+                'type="integer"',
+                'example=1',
+            ],
+        ];
+        $this->assertEquals($expectedWithoutEnum, $this->annotationGenerator->buildSchemaObjectArray('integer', '', NoDefaultValue::class, '1', ['1', '2']));
     }
 
     /**