diff --git a/src/ClientBuilder.php b/src/ClientBuilder.php
index b8c49c3..3b11299 100644
--- a/src/ClientBuilder.php
+++ b/src/ClientBuilder.php
@@ -10,6 +10,7 @@
 use Reqxide\Contract\TransportInterface;
 use Reqxide\Cookie\CookieJar;
 use Reqxide\Emulation\Browser;
+use Reqxide\Emulation\Platform;
 use Reqxide\Emulation\Profile;
 use Reqxide\Middleware\CompressionMiddleware;
 use Reqxide\Middleware\CookieMiddleware;
@@ -27,6 +28,8 @@ final class ClientBuilder
 
     private ?Profile $profile = null;
 
+    private ?Platform $platform = null;
+
     private ?TransportInterface $transport = null;
 
     private ?Proxy $proxy = null;
@@ -64,6 +67,13 @@ public function profile(Profile $profile): self
         return $this;
     }
 
+    public function platform(Platform $platform): self
+    {
+        $this->platform = $platform;
+
+        return $this;
+    }
+
     public function transport(TransportInterface $transport): self
     {
         $this->transport = $transport;
@@ -145,6 +155,11 @@ public function build(): Client
         // Resolve profile
         $profile = $this->profile ?? $this->browser?->profile() ?? new Profile;
 
+        // Apply platform overrides to profile headers
+        if ($this->platform instanceof Platform) {
+            $profile = $this->applyPlatform($profile, $this->platform);
+        }
+
         // Resolve transport
         $transport = $this->transport ?? TransportFactory::create();
 
@@ -172,6 +187,62 @@ public function build(): Client
         );
     }
 
+    private function applyPlatform(Profile $profile, Platform $platform): Profile
+    {
+        $headers = $profile->defaultHeaders;
+
+        if (isset($headers['User-Agent'])) {
+            $headers['User-Agent'] = $this->rewriteUserAgent($headers['User-Agent'], $platform);
+        }
+
+        if (isset($headers['sec-ch-ua-platform'])) {
+            $headers['sec-ch-ua-platform'] = $platform->secChUaPlatform();
+        }
+
+        if (isset($headers['sec-ch-ua-mobile'])) {
+            $headers['sec-ch-ua-mobile'] = $platform->isMobile() ? '?1' : '?0';
+        }
+
+        return new Profile(
+            tlsOptions: $profile->tlsOptions,
+            http2Options: $profile->http2Options,
+            http1Options: $profile->http1Options,
+            defaultHeaders: $headers,
+            originalHeaderMap: $profile->originalHeaderMap,
+            connectionGroup: $profile->connectionGroup,
+            impersonateTarget: $profile->impersonateTarget,
+        );
+    }
+
+    private function rewriteUserAgent(string $ua, Platform $platform): string
+    {
+        $platformString = $platform->userAgentPlatform();
+
+        // Chrome/Edge: Mozilla/5.0 ({platform}) AppleWebKit/...
+        if (preg_match('#^(Mozilla/5\.0 \()([^)]+)(\) AppleWebKit/537\.36.+)$#', $ua, $m)) {
+            if ($platform === Platform::IOS) {
+                $suffix = preg_replace('#Chrome/[\d.]+#', 'CriOS/$0', $m[3]) ?? $m[3];
+                $suffix = str_replace('CriOS/CriOS/', 'CriOS/', $suffix);
+
+                return $m[1].$platformString.$suffix;
+            }
+
+            return $m[1].$platformString.$m[3];
+        }
+
+        // Firefox: Mozilla/5.0 ({platform}; rv:{ver}) Gecko/...
+        if (preg_match('#^(Mozilla/5\.0 \()([^;]+(?:;[^)]*)?)(; rv:[\d.]+\) Gecko/.+)$#', $ua, $m)) {
+            return $m[1].$platformString.$m[3];
+        }
+
+        // Safari: Mozilla/5.0 ({platform}) AppleWebKit/605...
+        if (preg_match('#^(Mozilla/5\.0 \()([^)]+)(\) AppleWebKit/605.+)$#', $ua, $m)) {
+            return $m[1].$platformString.$m[3];
+        }
+
+        return $ua;
+    }
+
     /** @return list<MiddlewareInterface> */
     private function buildMiddlewares(): array
     {
diff --git a/src/Emulation/Browser.php b/src/Emulation/Browser.php
index dc6c5c3..e77042c 100644
--- a/src/Emulation/Browser.php
+++ b/src/Emulation/Browser.php
@@ -115,4 +115,11 @@ public function impersonateTarget(): ?string
             default => null,
         };
     }
+
+    public static function random(): self
+    {
+        $cases = self::cases();
+
+        return $cases[array_rand($cases)];
+    }
 }
diff --git a/src/Emulation/Platform.php b/src/Emulation/Platform.php
new file mode 100644
index 0000000..b124f26
--- /dev/null
+++ b/src/Emulation/Platform.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Reqxide\Emulation;
+
+enum Platform: string
+{
+    case MacOS = 'macos';
+    case Windows = 'windows';
+    case Linux = 'linux';
+    case Android = 'android';
+    case IOS = 'ios';
+
+    public function secChUaPlatform(): string
+    {
+        return match ($this) {
+            self::MacOS => '"macOS"',
+            self::Windows => '"Windows"',
+            self::Linux => '"Linux"',
+            self::Android => '"Android"',
+            self::IOS => '"iOS"',
+        };
+    }
+
+    public function isMobile(): bool
+    {
+        return match ($this) {
+            self::Android, self::IOS => true,
+            default => false,
+        };
+    }
+
+    public function userAgentPlatform(): string
+    {
+        return match ($this) {
+            self::MacOS => 'Macintosh; Intel Mac OS X 10_15_7',
+            self::Windows => 'Windows NT 10.0; Win64; x64',
+            self::Linux => 'X11; Linux x86_64',
+            self::Android => 'Linux; Android 10; K',
+            self::IOS => 'iPhone; CPU iPhone OS 18_0 like Mac OS X',
+        };
+    }
+
+    public static function random(): self
+    {
+        $cases = self::cases();
+
+        return $cases[array_rand($cases)];
+    }
+}
diff --git a/tests/Unit/ClientBuilderTest.php b/tests/Unit/ClientBuilderTest.php
index fc0e3a9..3204074 100644
--- a/tests/Unit/ClientBuilderTest.php
+++ b/tests/Unit/ClientBuilderTest.php
@@ -11,6 +11,7 @@
 use Reqxide\Contract\TransportInterface;
 use Reqxide\Cookie\CookieJar;
 use Reqxide\Emulation\Browser;
+use Reqxide\Emulation\Platform;
 use Reqxide\Emulation\Profile;
 use Reqxide\Proxy\Proxy;
 use Reqxide\Redirect\RedirectPolicy;
@@ -264,6 +265,52 @@ public function supportsHttp2Configuration(): bool
     expect($builder)->toBeInstanceOf(ClientBuilder::class);
 });
 
+it('platform overrides sec-ch-ua-platform and User-Agent', function (): void {
+    $transport = createMockTransport();
+    $client = Client::builder()
+        ->emulation(Browser::Chrome145)
+        ->platform(Platform::Windows)
+        ->transport($transport)
+        ->build();
+
+    $request = new Request('GET', 'https://example.com');
+    $client->sendRequest($request);
+
+    expect($transport->lastProfile->defaultHeaders['sec-ch-ua-platform'])->toBe('"Windows"')
+        ->and($transport->lastProfile->defaultHeaders['sec-ch-ua-mobile'])->toBe('?0')
+        ->and($transport->lastProfile->defaultHeaders['User-Agent'])->toContain('Windows NT 10.0');
+});
+
+it('platform Android sets mobile flag', function (): void {
+    $transport = createMockTransport();
+    $client = Client::builder()
+        ->emulation(Browser::Chrome145)
+        ->platform(Platform::Android)
+        ->transport($transport)
+        ->build();
+
+    $request = new Request('GET', 'https://example.com');
+    $client->sendRequest($request);
+
+    expect($transport->lastProfile->defaultHeaders['sec-ch-ua-mobile'])->toBe('?1')
+        ->and($transport->lastProfile->defaultHeaders['sec-ch-ua-platform'])->toBe('"Android"')
+        ->and($transport->lastProfile->defaultHeaders['User-Agent'])->toContain('Android');
+});
+
+it('platform does not affect profile without relevant headers', function (): void {
+    $transport = createMockTransport();
+    $client = Client::builder()
+        ->profile(new Profile(defaultHeaders: ['X-Custom' => 'value']))
+        ->platform(Platform::Linux)
+        ->transport($transport)
+        ->build();
+
+    $request = new Request('GET', 'https://example.com');
+    $client->sendRequest($request);
+
+    expect($transport->lastProfile->defaultHeaders)->toBe(['X-Custom' => 'value']);
+});
+
 it('profile takes precedence over emulation', function (): void {
     $transport = createMockTransport();
     $customProfile = new Profile(defaultHeaders: ['X-Source' => 'custom-profile']);
diff --git a/tests/Unit/Emulation/PlatformTest.php b/tests/Unit/Emulation/PlatformTest.php
new file mode 100644
index 0000000..dbc5726
--- /dev/null
+++ b/tests/Unit/Emulation/PlatformTest.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+use Reqxide\Emulation\Platform;
+
+it('has the correct number of cases', function (): void {
+    expect(Platform::cases())->toHaveCount(5);
+});
+
+it('has correct backed values', function (Platform $case, string $expected): void {
+    expect($case->value)->toBe($expected);
+})->with([
+    [Platform::MacOS, 'macos'],
+    [Platform::Windows, 'windows'],
+    [Platform::Linux, 'linux'],
+    [Platform::Android, 'android'],
+    [Platform::IOS, 'ios'],
+]);
+
+it('returns correct sec-ch-ua-platform', function (Platform $case, string $expected): void {
+    expect($case->secChUaPlatform())->toBe($expected);
+})->with([
+    [Platform::MacOS, '"macOS"'],
+    [Platform::Windows, '"Windows"'],
+    [Platform::Linux, '"Linux"'],
+    [Platform::Android, '"Android"'],
+    [Platform::IOS, '"iOS"'],
+]);
+
+it('identifies mobile platforms', function (): void {
+    expect(Platform::Android->isMobile())->toBeTrue()
+        ->and(Platform::IOS->isMobile())->toBeTrue()
+        ->and(Platform::MacOS->isMobile())->toBeFalse()
+        ->and(Platform::Windows->isMobile())->toBeFalse()
+        ->and(Platform::Linux->isMobile())->toBeFalse();
+});
+
+it('returns platform-specific UA string', function (Platform $case): void {
+    expect($case->userAgentPlatform())->toBeString()->not->toBeEmpty();
+})->with(Platform::cases());
+
+it('random returns a valid Platform', function (): void {
+    $platform = Platform::random();
+
+    expect($platform)->toBeInstanceOf(Platform::class);
+});