# System WebView Shell
[TOC]
WebView team maintains a "shell"—a thin interface over the WebView
APIs—to exercise WebView functionality. The System WebView Shell (AKA
"shell browser," "WebView shell") is a standalone app implemented [in
chromium](/android_webview/tools/system_webview_shell/). While often used for
manual testing, we also use the shell for automated tests (see our [layout and
page cycler tests](./test-instructions.md#layout-tests-and-page-cycler-tests)).
*** note
This relies on the WebView installed on the system. So if you're trying to
verify local changes to WebView, or run against a specific WebView build, you
must **install WebView first.**
***
*** promo
**Tip:** the shell displays the WebView version (the corresponding [chromium version
number](https://www.chromium.org/developers/version-numbers)) in the title bar
at the top. This can be helpful for checking which WebView version is installed
& selected on the device.
***
*** note
This is *not* a production quality browser and does not implement suitable
security UI to be used for anything other than testing WebView. This should not
be shipped anywhere or used as the basis for implementing a browser.
***
## Setting up the build
WebView shell only requires `target_os = "android"`. The simplest option is to
just reuse the same out/ folder and GN args you would normally use for WebView
or Chrome for Android.
*** note
**For the emulator:** the emulator comes with WebView shell preinstalled with a
different signing key, so installation will fail with
`INSTALL_FAILED_UPDATE_INCOMPATIBLE: Package ... signatures do not match
previously installed version`. You can workaround this in your GN args with
`system_webview_shell_package_name = "org.chromium.my_webview_shell"`.
Your local build will install alongside the preinstalled WebView shell. You may
hide the preinstalled shell by running `adb root` followed by `adb shell pm
disable org.chromium.webview_shell` in your terminal (copy-paste the command
as-written, **don't** use the package name from the GN arg above).
***
## Building the shell
```sh
$ autoninja -C out/Default system_webview_shell_apk
```
## Installing the shell
```sh
$ out/Default/bin/system_webview_shell_apk install
```
## Running the shell
```sh
# Launch a URL from the commandline, or open the app from the app launcher
$ out/Default/bin/system_webview_shell_apk launch "https://www.google.com/"
# For more commands:
$ out/Default/bin/system_webview_shell_apk --help
```
*** note
**Note:** `system_webview_shell_apk` does not support modifying CLI flags. See
https://crbug.com/959425. Instead, you should modify WebView's flags by
following [commandline-flags.md](./commandline-flags.md).
***
## Prebuilt APKs
We maintain a **public** archive of prebuilt WebView shell APKs. This saves you
the effort of setting up a chromium checkout just for the sake of compiling this
test app. You can download a prebuilt APK from this cloud storage bucket:
https://storage.googleapis.com/chromium-browser-snapshots/index.html?prefix=Android/
1. Click on the "name" column header **twice**. This will force the page to sort
the newest builds toward the top. Click the folder with the largest number,
ignoring the `LAST_CHANGE` and `refs_heads_main-*/` folders.
* Your WebView shell version **does not** need to match your device's
WebView version. We recommend using the latest WebView shell build
regardless of your WebView version to make sure you have the latest
features and bug fixes of the shell app itself.
1. Click `chrome-android.zip` to download the archived APKs. Unzip this and look
for a file named `SystemWebViewShell.apk`.
1. Now you can install this like any other APK:
```sh
# Install adb if it's not already installed:
$ which adb || sudo apt install adb
# Replace this path with the path to your downloaded APK
$ adb install -d -r ~/Downloads/chrome-android/SystemWebViewShell.apk
```
*** note
**Note:** on the Android emulator, this may fail to install and print the
`INSTALL_FAILED_UPDATE_INCOMPATIBLE: Package ... signatures do not match
previously installed version` error message. This may require switching to a
physical device or compiling the WebView shell from source (see the
troubleshooting steps below).
***
## Troubleshooting
### INSTALL\_FAILED\_UPDATE\_INCOMPATIBLE: Package ... signatures do not match previously installed version
This may be happening because the shell is preinstalled on your device (ex. this
is the case on all emulators). **The easiest way** to workaround this is to
[change the shell's package name in a local build](#building-for-the-emulator).
If you don't want to (or can't) change the package name, then you may be able to
modify your device's system image. See the [manual steps for removing system
apps](removing-system-apps.md) and replace **com.google.android.webview** with
**org.chromium.webview_shell**.
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