diff --git a/config/nativephp.php b/config/nativephp.php
index 7ae7ca05..f3ab13f5 100644
--- a/config/nativephp.php
+++ b/config/nativephp.php
@@ -128,7 +128,7 @@
         'storage/framework/sessions',
         'storage/framework/cache',
         'storage/framework/testing',
-        'storage/logs/laravel.log'
+        'storage/logs/laravel.log',
     ],
 
     /*
diff --git a/src/Commands/InstallCommand.php b/src/Commands/InstallCommand.php
index 186f1dbb..9733dff7 100644
--- a/src/Commands/InstallCommand.php
+++ b/src/Commands/InstallCommand.php
@@ -5,7 +5,7 @@
 use GuzzleHttp\Client;
 use GuzzleHttp\Exception\RequestException;
 use Illuminate\Console\Command;
-use Illuminate\Support\Facades\File;
+use Native\Mobile\Support\AppIdValidator;
 use Native\Mobile\Traits\DisplaysMarketingBanners;
 use Native\Mobile\Traits\InstallsAndroid;
 use Native\Mobile\Traits\InstallsIos;
@@ -209,6 +209,7 @@ protected function ensureAppIdIsSet(): void
             placeholder: $suggestedAppId,
             default: $suggestedAppId,
             hint: 'This uniquely identifies your app on the App Store and Google Play',
+            validate: fn (string $value) => AppIdValidator::validateForPrompt($value),
         );
 
         $this->setEnvValue('NATIVEPHP_APP_ID', $appId);
diff --git a/src/Commands/RunCommand.php b/src/Commands/RunCommand.php
index 0cdc0ac0..09ae2759 100644
--- a/src/Commands/RunCommand.php
+++ b/src/Commands/RunCommand.php
@@ -5,6 +5,7 @@
 use GuzzleHttp\Client;
 use Illuminate\Console\Command;
 use Native\Mobile\Plugins\PluginRegistry;
+use Native\Mobile\Support\AppIdValidator;
 use Native\Mobile\Traits\DisplaysMarketingBanners;
 use Native\Mobile\Traits\ManagesViteDevServer;
 use Native\Mobile\Traits\ManagesWatchman;
@@ -223,6 +224,22 @@ protected function ensureValidAppId(): void
         if (str($appId)->startsWith('com.nativephp.')) {
             warning('Please change your NATIVEPHP_APP_ID from the default value.');
         }
+
+        $errors = AppIdValidator::validate($appId);
+
+        if ($errors['android']) {
+            error('Invalid app ID for Android: '.$errors['android']);
+        }
+
+        if ($errors['ios']) {
+            error('Invalid app ID for iOS: '.$errors['ios']);
+        }
+
+        if ($errors['android'] || $errors['ios']) {
+            note('Please fix NATIVEPHP_APP_ID in your .env file.');
+            note('A valid app ID looks like: com.yourcompany.yourapp');
+            exit(1);
+        }
     }
 
     protected function updateStartUrl(string $startUrl): void
diff --git a/src/Plugins/Compilers/AndroidPluginCompiler.php b/src/Plugins/Compilers/AndroidPluginCompiler.php
index 07ea6822..bcabb52b 100644
--- a/src/Plugins/Compilers/AndroidPluginCompiler.php
+++ b/src/Plugins/Compilers/AndroidPluginCompiler.php
@@ -936,7 +936,7 @@ protected function buildRepositoryBlock(array $repo): ?string
 
             $authBlock = '';
             if ($authentication === 'basic') {
-                $authBlock = <<<KOTLIN
+                $authBlock = <<<'KOTLIN'
 
                 authentication {
                     create<BasicAuthentication>("basic")
diff --git a/src/Support/AppIdValidator.php b/src/Support/AppIdValidator.php
new file mode 100644
index 00000000..4b817b59
--- /dev/null
+++ b/src/Support/AppIdValidator.php
@@ -0,0 +1,86 @@
+<?php
+
+namespace Native\Mobile\Support;
+
+class AppIdValidator
+{
+    /**
+     * Validate an app ID for Android (Java package name rules).
+     * Each segment must start with a letter and contain only letters, digits, and underscores.
+     */
+    public static function validateForAndroid(string $appId): ?string
+    {
+        if (trim($appId) === '') {
+            return 'App ID cannot be empty.';
+        }
+
+        $segments = explode('.', $appId);
+
+        if (count($segments) < 2) {
+            return 'App ID must have at least two segments (e.g. com.example).';
+        }
+
+        foreach ($segments as $segment) {
+            if ($segment === '') {
+                return 'App ID must not contain empty segments.';
+            }
+
+            if (! preg_match('/^[a-zA-Z][a-zA-Z0-9_]*$/', $segment)) {
+                return "Invalid Android app ID segment \"{$segment}\". Each segment must start with a letter and contain only letters, digits, and underscores. Hyphens are not allowed.";
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Validate an app ID for iOS (bundle identifier rules).
+     * Each segment must start and end with an alphanumeric character, and may contain hyphens in between.
+     */
+    public static function validateForIos(string $appId): ?string
+    {
+        if (trim($appId) === '') {
+            return 'App ID cannot be empty.';
+        }
+
+        $segments = explode('.', $appId);
+
+        if (count($segments) < 2) {
+            return 'App ID must have at least two segments (e.g. com.example).';
+        }
+
+        foreach ($segments as $segment) {
+            if ($segment === '') {
+                return 'App ID must not contain empty segments.';
+            }
+
+            if (! preg_match('/^[a-zA-Z0-9]([a-zA-Z0-9-]*[a-zA-Z0-9])?$/', $segment)) {
+                return "Invalid iOS bundle ID segment \"{$segment}\". Each segment must start and end with a letter or digit, and may contain hyphens in between.";
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Validate an app ID for both platforms.
+     *
+     * @return array{android: string|null, ios: string|null}
+     */
+    public static function validate(string $appId): array
+    {
+        return [
+            'android' => static::validateForAndroid($appId),
+            'ios' => static::validateForIos($appId),
+        ];
+    }
+
+    /**
+     * Validate an app ID for use in a prompt validation closure.
+     * Returns the first error found (Android rules are strictest), or null if valid for both platforms.
+     */
+    public static function validateForPrompt(string $appId): ?string
+    {
+        return static::validateForAndroid($appId) ?? static::validateForIos($appId);
+    }
+}
diff --git a/src/Traits/ValidatesAppConfig.php b/src/Traits/ValidatesAppConfig.php
index 7dae8238..120db08b 100644
--- a/src/Traits/ValidatesAppConfig.php
+++ b/src/Traits/ValidatesAppConfig.php
@@ -2,6 +2,8 @@
 
 namespace Native\Mobile\Traits;
 
+use Native\Mobile\Support\AppIdValidator;
+
 trait ValidatesAppConfig
 {
     private function validateAppVersion(string $buildType): void
@@ -41,5 +43,21 @@ protected function validateAppId(): void
         if (str($appId)->startsWith('com.nativephp.')) {
             \Laravel\Prompts\warning('Please change your NATIVEPHP_APP_ID. Must not contain "nativephp"');
         }
+
+        $errors = AppIdValidator::validate($appId);
+
+        if ($errors['android']) {
+            \Laravel\Prompts\error('Invalid app ID for Android: '.$errors['android']);
+        }
+
+        if ($errors['ios']) {
+            \Laravel\Prompts\error('Invalid app ID for iOS: '.$errors['ios']);
+        }
+
+        if ($errors['android'] || $errors['ios']) {
+            $this->line('Please fix NATIVEPHP_APP_ID in your .env file.');
+            $this->line('A valid app ID looks like: com.yourcompany.yourapp');
+            exit(1);
+        }
     }
 }
diff --git a/tests/Unit/AppIdValidatorTest.php b/tests/Unit/AppIdValidatorTest.php
new file mode 100644
index 00000000..19d377ea
--- /dev/null
+++ b/tests/Unit/AppIdValidatorTest.php
@@ -0,0 +1,154 @@
+<?php
+
+namespace Tests\Unit;
+
+use Native\Mobile\Support\AppIdValidator;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Tests\TestCase;
+
+class AppIdValidatorTest extends TestCase
+{
+    // --- Android validation ---
+
+    #[DataProvider('validAndroidIds')]
+    public function test_valid_android_ids(string $appId): void
+    {
+        $this->assertNull(AppIdValidator::validateForAndroid($appId));
+    }
+
+    public static function validAndroidIds(): array
+    {
+        return [
+            'simple two segments' => ['com.example'],
+            'three segments' => ['com.example.myapp'],
+            'with underscore' => ['com.example.my_app'],
+            'with digits' => ['com.example.app123'],
+            'uppercase' => ['com.Example.MyApp'],
+            'many segments' => ['com.example.sub.package.app'],
+        ];
+    }
+
+    #[DataProvider('invalidAndroidIds')]
+    public function test_invalid_android_ids(string $appId): void
+    {
+        $this->assertNotNull(AppIdValidator::validateForAndroid($appId));
+    }
+
+    public static function invalidAndroidIds(): array
+    {
+        return [
+            'empty string' => [''],
+            'single segment' => ['myapp'],
+            'hyphen in segment' => ['com.example.my-app'],
+            'segment starts with digit' => ['com.123example.app'],
+            'empty segment (double dot)' => ['com..example'],
+            'trailing dot' => ['com.example.'],
+            'leading dot' => ['.com.example'],
+            'spaces' => ['com .example'],
+            'special characters' => ['com.example.my@app'],
+        ];
+    }
+
+    // --- iOS validation ---
+
+    #[DataProvider('validIosIds')]
+    public function test_valid_ios_ids(string $appId): void
+    {
+        $this->assertNull(AppIdValidator::validateForIos($appId));
+    }
+
+    public static function validIosIds(): array
+    {
+        return [
+            'simple two segments' => ['com.example'],
+            'three segments' => ['com.example.myapp'],
+            'with hyphen' => ['com.example.my-app'],
+            'with digits' => ['com.example.app123'],
+            'segment starts with digit' => ['com.1example.app'],
+            'uppercase' => ['com.Example.MyApp'],
+            'many segments' => ['com.example.sub.package.app'],
+        ];
+    }
+
+    #[DataProvider('invalidIosIds')]
+    public function test_invalid_ios_ids(string $appId): void
+    {
+        $this->assertNotNull(AppIdValidator::validateForIos($appId));
+    }
+
+    public static function invalidIosIds(): array
+    {
+        return [
+            'empty string' => [''],
+            'single segment' => ['myapp'],
+            'empty segment (double dot)' => ['com..example'],
+            'trailing dot' => ['com.example.'],
+            'leading dot' => ['.com.example'],
+            'segment starts with hyphen' => ['com.-example.app'],
+            'segment ends with hyphen' => ['com.example-.app'],
+            'underscore' => ['com.example.my_app'],
+        ];
+    }
+
+    // --- Cross-platform hyphens ---
+
+    public function test_hyphens_rejected_for_android_allowed_for_ios(): void
+    {
+        $appId = 'com.japseyz.ikast-musikliv';
+
+        $this->assertNotNull(AppIdValidator::validateForAndroid($appId));
+        $this->assertNull(AppIdValidator::validateForIos($appId));
+    }
+
+    // --- Cross-platform validate() ---
+
+    public function test_validate_returns_both_platforms(): void
+    {
+        $result = AppIdValidator::validate('com.example.myapp');
+
+        $this->assertArrayHasKey('android', $result);
+        $this->assertArrayHasKey('ios', $result);
+        $this->assertNull($result['android']);
+        $this->assertNull($result['ios']);
+    }
+
+    public function test_validate_returns_errors_for_both_platforms(): void
+    {
+        // Single segment is invalid for both
+        $result = AppIdValidator::validate('myapp');
+
+        $this->assertNotNull($result['android']);
+        $this->assertNotNull($result['ios']);
+    }
+
+    public function test_validate_returns_android_error_only_for_hyphens(): void
+    {
+        $result = AppIdValidator::validate('com.example.my-app');
+
+        $this->assertNotNull($result['android']);
+        $this->assertNull($result['ios']);
+    }
+
+    // --- validateForPrompt() ---
+
+    public function test_validate_for_prompt_returns_null_for_valid(): void
+    {
+        $this->assertNull(AppIdValidator::validateForPrompt('com.example.myapp'));
+    }
+
+    public function test_validate_for_prompt_returns_string_for_invalid(): void
+    {
+        $result = AppIdValidator::validateForPrompt('com.example.my-app');
+
+        $this->assertIsString($result);
+        $this->assertNotEmpty($result);
+    }
+
+    public function test_validate_for_prompt_returns_android_error_first(): void
+    {
+        // Hyphens fail Android but pass iOS — prompt should return the Android error
+        $result = AppIdValidator::validateForPrompt('com.example.my-app');
+
+        $this->assertStringContainsString('Android', $result);
+    }
+}