# Developing User-Agent
User-Agent (UA) is a special string that contains key information such as the device type, operating system, and version. In web development, UA is used by the server to identify the source device of the request and its features, so that the server can provide custom content and services. If UAs cannot be correctly identified on a page, multiple exceptions may occur. For example, a page layout optimized for a mobile device may be displayed in disorder on a desktop device, and vice versa. In addition, some browser functionalities or CSS attributes are supported only in specific browser versions. If a page cannot successfully identify the UA, rendering problems or logic errors may occur.
## Default User-Agent Structure
- String format
```ts
Mozilla/5.0 ({DeviceType}; {OSName} {OSVersion}) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/{ChromeCompatibleVersion}.0.0.0 Safari/537.36 ArkWeb/{ArkWeb VersionCode} {DeviceCompat} {Extension}
```
- Example
```ts
Mozilla/5.0 (Phone; OpenHarmony 5.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/114.0.0.0 Safari/537.36 ArkWeb/4.1.6.1 Mobile
```
- Fields
| Field | Description |
| --------------------- | ------------------------------------------------------------ |
| DeviceType | Device type.
The value can be:
- **Phone**
- **Tablet**
- **PC** (2-in-1 device)|
| OSName | OS name.
Default value: **OpenHarmony** |
| OSVersion | OS version. The value is a two-digit number, in M.S format.
You can obtain the value by extracting the first two digits of the version number from the system parameter **const.ohos.fullname**.
Default value: **5.0** |
| ChromeCompatibleVersion | The version that is compatible with the main Chrome version. The earliest version is 114.
Default value: **114** |
| ArkWeb | Web kernel name of the OpenHarmony version.
Default value: **ArkWeb** |
| ArkWeb VersionCode | ArkWeb version number, in the format of a.b.c.d.
Default value: **4.1.6.1** |
| DeviceCompat | Forward compatibility settings.
Default value: **Mobile** |
| Extension | Field that can be extended by a third-party application.
When a third-party application uses the **Web** component, UA can be extended. For example, an application information identifier can be added.|
> **NOTE**
>
> - Currently, there are two spaces before the **ArkWeb** field of the default **User-Agent**.
>
> - The **viewport** parameter of the **meta** tag on the frontend HTML page is enabled or disabled based on whether **User-Agent** contains the **Mobile** field. If **User-Agent** does not contain the **Mobile** field, the **viewport** attribute in the **meta** tag is disabled by default. In this case, you can explicitly set [metaViewport](../reference/apis-arkweb/arkts-basic-components-web-attributes.md#metaviewport12) to **true** to enable the **viewport** attribute.
>
> - You are advised to use the **OpenHarmony** keyword to identify whether a device is an OpenHarmony device, and use the **DeviceType** keyword to identify the device type for page display on different devices. (The **ArkWeb** keyword indicates the web kernel of the device, and the **OpenHarmony** keyword indicates the operating system of the device.)
>
> - The **{DistributionOSName}** and **{DistributionOSVersion}** fields are not supported in versions earlier than API version 15. Since API version 15, they are not displayed in the default **User-Agent**.
## Custom User-Agent Structure
In the following example, [getUserAgent()](../reference/apis-arkweb/arkts-apis-webview-WebviewController.md#getuseragent) is used to obtain the default **User-Agent** string, which you can modify or extend as needed.
```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';
@Entry
@Component
struct WebComponent {
controller: webview.WebviewController = new webview.WebviewController();
build() {
Column() {
Button('getUserAgent')
.onClick(() => {
try {
let userAgent = this.controller.getUserAgent();
console.log("userAgent: " + userAgent);
} catch (error) {
console.error(`ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
})
Web({ src: 'www.example.com', controller: this.controller })
}
}
}
```
In the following example, [setCustomUserAgent()](../reference/apis-arkweb/arkts-apis-webview-WebviewController.md#setcustomuseragent10) is used to set a custom user agent, which overwrites the default user agent. Therefore, you are advised to add the extension field to the end of the default user agent. For example, to develop a third-party application, you can add a specific application identifier while maintaining the original user agent information.
When **src** of the **Web** component is set to a URL, set **User-Agent** in **onControllerAttached**. For details, see the following example. Avoid setting the user agent in **onLoadIntercept**. Otherwise, the setting may fail occasionally. If **User-Agent** is not set in **onControllerAttached**, calling **setCustomUserAgent** may cause mismatches between the loaded page and the intended user agent.
When **src** of the **Web** component is set to an empty string, call **setCustomUserAgent** to set **User-Agent** and then use **loadUrl** to load a specific page.
```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';
@Entry
@Component
struct WebComponent {
controller: webview.WebviewController = new webview.WebviewController();
// Third-party application information identifier
@State customUserAgent: string = ' DemoApp';
build() {
Column() {
Web({ src: 'www.example.com', controller: this.controller })
.onControllerAttached(() => {
console.log("onControllerAttached");
try {
let userAgent = this.controller.getUserAgent() + this.customUserAgent;
this.controller.setCustomUserAgent(userAgent);
} catch (error) {
console.error(`ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
})
}
}
}
```
Since API version 20, you can use the [setAppCustomUserAgent()](../reference/apis-arkweb/arkts-apis-webview-WebviewController.md#setappcustomuseragent20) API to set an application-level custom user agent or use the [setUserAgentForHosts()](../reference/apis-arkweb/arkts-apis-webview-WebviewController.md#setuseragentforhosts20) API to set an application-level custom user agent for a specific website. The custom user agent overwrites the system user agent and takes effect for all **Web** components in the application.
You are advised to call the **setAppCustomUserAgent** and **setUserAgentForHosts** methods to set **User-Agent** before creating a **Web** component, and then create a **Web** component with a specified **src** or use **loadUrl** to load a specific page.
```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';
@Entry
@Component
struct WebComponent {
controller: webview.WebviewController = new webview.WebviewController();
aboutToAppear(): void {
try {
webview.WebviewController.initializeWebEngine();
let defaultUserAgent = webview.WebviewController.getDefaultUserAgent();
let appUA = " appUA";
webview.WebviewController.setUserAgentForHosts(
appUA,
[
"www.example.com",
"www.baidu.com"
]
);
} catch (error) {
console.error(`ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
}
build() {
Column() {
Web({ src: 'www.example.com', controller: this.controller })
}
}
}
```
In the following example, [getCustomUserAgent()](../reference/apis-arkweb/arkts-apis-webview-WebviewController.md#getcustomuseragent10) is used to obtain the custom user agent.
```ts
// xxx.ets
import { webview } from '@kit.ArkWeb';
import { BusinessError } from '@kit.BasicServicesKit';
@Entry
@Component
struct WebComponent {
controller: webview.WebviewController = new webview.WebviewController();
@State userAgent: string = '';
build() {
Column() {
Button('getCustomUserAgent')
.onClick(() => {
try {
this.userAgent = this.controller.getCustomUserAgent();
console.log("userAgent: " + this.userAgent);
} catch (error) {
console.error(`ErrorCode: ${(error as BusinessError).code}, Message: ${(error as BusinessError).message}`);
}
})
Web({ src: 'www.example.com', controller: this.controller })
}
}
}
```
## User-Agent API Priority
| API| Priority| Description|
| -------- | -------- | -------- |
| setCustomUserAgent | Highest| Takes effect for the called **Web** component.|
| setUserAgentForHosts | Lower than **setCustomUserAgent**| Takes effect for all **Web** components in the application to access the specified website.|
| setAppCustomUserAgent | Lower than **setUserAgentForHosts**| Takes effect for all **Web** components in the application.|
| Default UA of ArkWeb| Lowest| Takes effect for all **Web** components in the application. This parameter is read-only and can be obtained using **getDefaultUserAgent**.|
## FAQs
### How do I use User-Agent to identify different OpenHarmony devices?
OpenHarmony devices can be identified based on the OS name, OS version, and device type in **User-Agent**. You are advised to check all of them to ensure accurate device identification.
1. Identification based on the OS name
Use the **{OSName}** field.
```ts
const isOpenHarmony = () => /OpenHarmony/i.test(navigator.userAgent);
```
2. Identification based on the OS version
Use the **{OSName}** and **{OSVersion}** fields. The format is **OpenHarmony + Version number**.
```ts
const matches = navigator.userAgent.match(/OpenHarmony (\d+\.?\d*)/);
matches?.length && Number(matches[1]) >= 5;
```
3. Identification based on the device type
Use the **deviceType** field.
```ts
// Check whether the device is a mobile phone.
const isPhone = () => /Phone/i.test(navigator.userAgent);
// Check whether the device is a tablet.
const isTablet = () => /Tablet/i.test(navigator.userAgent);
// Check whether the device is a 2-in-1 device.
const is2in1 = () => /PC/i.test(navigator.userAgent);
```
### How do I simulate the User-Agent of OpenHarmony for frontend debugging?
In Windows, macOS, and Linux, you can use the **User-Agent** rewriting capability provided by DevTools to simulate the OpenHarmony **User-Agent** in Chrome, Edge, and Firefox.