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WebView2 browser flags

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One of the ways you can interact with Microsoft Edge WebView2 and impact behavior is by passing browser flags (arguments, or switches) to WebView2. These browser flags are useful for testing forthcoming features, and for diagnosing issues.

Warning

Apps in production shouldn't use WebView2 browser flags, because these flags might be removed or altered at any time, and aren't necessarily supported long-term.

Generally, the flags are owned by both Chromium and Microsoft Edge. Chromium flags are not owned or controlled by Microsoft Edge, so Microsoft Edge doesn't have control over when or how the flags are removed or altered in their behavior.

You can set browser flags in your local device environment, or set browser flags programmatically through code. Both approaches are described below.

Setting browser flags in your local device environment

To test forthcoming features or to diagnose issues, we recommend using browser flags in your local device environment, via setting the WEBVIEW2_ADDITIONAL_BROWSER_ARGUMENTS environment variable or via registry keys. For more information, see the following Win32 API Reference: CreateCoreWebView2EnvironmentWithOptions.

Setting browser flags programmatically through code

Instead of setting browser flags in your local device environment, an alternative approach is to set browser flags programmatically, by passing the browser flags as the AdditionalBrowserArguments property of CoreWebView2EnvironmentOptions. If you set browser flags programmatically, be sure to remove the flags in code before shipping your app, to avoid accidentally shipping the flags in production.

Available WebView2 browser flags

The following are some of the flags we've seen used.

Flag Description
accept-lang Specifies Accept-Language to send to servers and expose to JavaScript via the Navigator.language DOM property. The format is language[-country], where language is the 2-letter code from ISO-639.
allow-file-access-from-files Allows reading file:// URIs from other file:// URIs.
allow-insecure-localhost Enables TLS/SSL errors on localhost to be ignored, so that no interstitial is done and no blocking of requests is done.
allow-run-as-system By default, the Edge WebView browser exits if launched as System (launching as System is not recommended). This flag bypasses that check, so that even if the Edge WebView browser is launched as System, the Edge WebView browser doesn't exit.
allow-running-insecure-content Enables insecure content in Cast Web Runtime. This flag unblocks MSPs that serve content from HTTP sources.
auto-open-devtools-for-tabs Makes Edge WebView auto-open the DevTools window for each tab. For use by developers and by automation.
AutofillReplaceCachedWebElementsByRendererIds If enabled, replaces cached web elements in AutofillAgent and FormTracker by their renderer IDs.
autoplay-policy Command-line flag name to set the autoplay policy.
BlockInsecurePrivateNetworkRequests When this feature is enabled, private network requests that are initiated from non-secure contexts in the public address space are blocked.
block-new-web-contents If true, all pop-ups and calls to window.open fail.
BreakoutBoxPreferCaptureTimestampInVideoFrames Reverts the behavior of the Timestamp property of the CoreWebView2Texture class to match legacy behavior of WebView2 Runtime version 124 and earlier.
disable-background-timer-throttling Disables task throttling of timer tasks from background pages.
disable-domain-action-user-agent-override Disables the per-domain User Agent override from the Domain Actions feature.
disable-gpu Disables GPU hardware acceleration. If a software renderer isn't in place, the GPU process doesn't launch.
disable-gpu-driver-bug-workarounds Disables workarounds for various GPU driver bugs.
disable-site-isolation-trials Disables site isolation.
disable-web-security Disables cross-origin policy and doesn't enforce the same-origin policy. Use for website testing only.
disk-cache-size Forces the maximum disk space to be used by the disk cache, in bytes.
do-not-de-elevate Prevents de-elevation of the WebView2 on launch. Used after de-elevating, to prevent infinite loops.
edge-webview-debugging-script Runs PostWebMessage script asynchronously.
edge-webview-enable-mojo-ipcz Enables MojoIpcz (mojo-ipcz) for apps that use WebView2.
edge-webview-foreground-boost-opt-in Opts-in to foreground boost.
edge-webview-foreground-boost-opt-out Opts-out of foreground boost.
edge-webview-force-personal-context Forces Edge WebView browser processes to run in WIP personal context.
edge-webview-interactive-dragging Enables pointer events and focus events to occur on elements that have the --app-region: drag attribute. If this flag isn't set, drag elements are non-interactive.
edge-webview-is-background Indicates that WebView is being launched in the background.
edge-webview-no-dpi-workaround Disables the "DPI awareness app compatibility shim" workaround, which launches Edge WebView browser process via a shell, so that the process doesn't inherit the "app compat" shim.
edge-webview-run-with-package-id Runs WebView processes with a package identity (package ID) for a bridged Desktop app.
edge-webview-run-without-package-id Runs WebView processes without a package identity (package ID) for a bridged Desktop app.
embedded-browser-webview-dpi-awareness Sets the DPI awareness level of the server-side processes.
enable-experimental-web-platform-features Enables Web Platform features that are in development.
enable-logging Enable logging at the error level.
force-color-profile Force all monitors to be treated as though they have the specified color profile. Valid values: srgb, generic-rgb.
force-device-scale-factor Overrides the device scale factor for the Edge WebView browser UI and the contents.
force-fieldtrials Can be used to force field trials when testing changes locally. The argument is a list of name/value pairs, separated by forward slashes. If a trial name is prefixed with an asterisk, that trial will start activated. For example, the following argument defines two trials, with the second one activated: EdgeNow/Enable/*MaterialDesignNTP/Default/. This option can also be used by the browser process to send the list of trials to a non-browser process, using the same format.
force-fieldtrial-params Can be used to force parameters of field trials when testing changes locally. The argument is a parameter list of (key, value) pairs, prefixed by an associated (trial, group) pair. For multiple (trial, group) pairs, use a comma separator.
force-renderer-accessibility Whether to force renderer accessibility to be on, instead of enabling renderer accessibility on-demand when a screen reader is detected. The disable-renderer-accessibility flag overrides this flag, if the disable-renderer-accessibility flag is present.
HardwareMediaKeyHandling Enables handling of hardware media keys for controlling media.
ignore-certificate-errors Ignores certificate-related errors.
ignore-gpu-blocklist Whether to ignore the GPU blocklist.
incognito Forces Incognito mode even if user data directory is specified by using the --user-data-dir flag.
isolate-origins Require dedicated processes for a set of origins, specified as a comma-separated list. For example: --isolate-origins=https://www.foo.com,https://www.bar.com.
js-flags Specifies the flags passed to JS engine.
lang The language file that WebView2 want to try to open. Of the form language[-country] where language is the 2-letter code from ISO-639.
log-net-log Enables saving net log events to a file. If a value is given, that value is used as the directory path and file name. If no value is given, the file is named netlog.json, and is placed in the user data directory.
msAbydos Enables the "handwriting-to-text" experience.
msAbydosGestureSupport Allows users to use gestures (such as the scratchout gesture) to delete text by using a pen. Valid only if the msAbydos flag is enabled.
msAbydosHandwritingAttr Whether the "handwriting-to-text" experience is enabled for input elements at the DOM level. Valid only if the msAbydos flag is enabled.
msEdgeDesignerUI Use this flag to disable the Designer Shoreline App. This feature is not supported in WebView2.
msEdgeHubAppDesigner Use this flag to disable the Designer Shoreline App. This feature is not supported in WebView2.
msEdgeDesignerDriverFix Use this flag to disable getting content and automatically showing the Designer feature. This feature is not supported in WebView2.
msEdgeFluentOverlayScrollbar Force-enables Fluent Overlay scrollbars, overriding whatever value kFluentScrollbar may hold at the moment.
msEdgeDevToolsWdpRemoteDebugging Enables remote debugging. See Remote debugging WebView2 WinUI 2 (UWP) apps, Remotely debug Windows devices.
msEnhancedTextContrast Improves text contrast enhancement and gamma correction to match the quality and clarity of other native Windows applications. When this flag is used, font rendering respects user ClearType Tuner settings when applying text contrast enhancement and gamma correction.
msEnhancedTrackingPreventionEnabled Enables native privacy protection features, such as blocking cookies and web requests that reside in domains that are known to be tracking domains.
msFloatyMode If false, disables the Floaty feature. Use this flag to disable the Floaty feature, because WebView doesn't support browser retention experiments.
msFloatyShouldHonorIndiaHoldout If true, honors the India holdout group. Use this flag, set to false, to disable the Floaty feature that's enabled if the user is part of the India holdout group, because WebView doesn't support browser retention experiments.
msOverlayScrollbarWinStyle Whether the users can change between overlay and non-overlay modes for Fluent scrollbars.
msPdfEnableAsPreview This features enables the PDF viewer to launch with a minimal toolbar and in read-only preview mode.
msSingleSignOnOSForPrimaryAccountIsShared If enabled, allows implicit sign-in to Microsoft webpages using any account, by using the information from the primary OS account.
msSmartScreenProtection If enabled, SmartScreen protection will be available.
msUseSpellCheckCorrectionsCard If enabled, a new corrections card UI is shown when the user clicks a misspelled word.
msWebView2CancelInitialNavigation If enabled, cancels the initial navigation in WebView2 to improve startup performance.
msWebView2CodeCache If enabled, JavaScript resources that are loaded in a WebView2 app via SetVirtualHostNameToFolderMapping or add_WebResourceRequested are eligible for bytecode caching, which should speed up the third and subsequent loads. This feature also enables bytecode caching for any other components that use the DevTools network interception mechanism to provide custom responses (see Custom management of network requests).
msWebView2EnableDownloadContentInWebResourceResponseReceived If enabled, allow responses of navigations that become downloads to be available in WebResourceResponseReceived
msWebView2TextureStream If enabled, allows to stream captured or composed video frames to the WebView2 where JavaScript can render or otherwise interact with the frames via W3C standard DOM APIs including the Video element, and MediaStream.
msWebView2EnableDraggableRegions If true, enables webpages within WebView2 make use of the app-region: drag\|nodrag CSS style, which causes elements with that style to behave like a titlebar. Without this flag, the app-region: drag\|nodrag CSS style has no effect.
msWebView2CodeCache If enabled, JavaScript resources that are loaded in a WebView2 app via SetVirtualHostNameToFolderMapping or add_WebResourceRequested are eligible for bytecode caching, which should speed up the third and subsequent loads. This feature also enables bytecode caching for any other components that use the DevTools network interception mechanism to provide custom responses.
msWebView2NativeEventDispatch If enabled, uses a native mojo connection to dispatch internal events, such as web messages to a renderer process.
msWebView2SimulateMemoryPressureWhenInactive If enabled, simulates memory pressure for an inactive WebView.
msWebView2TreatAppSuspendAsDeviceSuspend If enabled, when all WebViews are suspended, WebView2 treats the app as if the device is suspended, and pauses all delayed tasks and timers.
no-proxy-server Overrides any other proxy server flags that are passed.
net-log-capture-mode Sets the granularity of events to capture in the network log. Valid values: Default, IncludeSensitive, Everything.
no-network-profile-warning If enabled, the browser warns if the UDF is on a network share. This flag is only supported on Windows; this flag is ignored on other platforms.
no-sandbox Disables the sandbox for all process types that are normally sandboxed. Meant to be used as a browser-level flag for testing purposes only.
no-first-run Skips First-Run tasks, regardless of whether it's actually the First Run, and skips displaying the What's New page. This flag is overridden by kForceFirstRun (for the First-Run Experience (FRE)) and by kForceWhatsNew (for displaying What's New). This flag doesn't drop the First Run sentinel, and thus doesn't prevent the First-Run experience from occurring the next time the Edge WebView browser is launched without this flag. This flag doesn't update the last What's New milestone, so doesn't prevent What's New from being displayed the next time the Edge WebView browser is launched without this flag.
PartitionedCookies When enabled, sites can opt-in to having their cookies partitioned by the top-level site by using the Partitioned attribute. Partitioned cookies are only sent when the browser is on the same top-level site that it was on when the cookie was set.
proxy-auto-detect Forces proxy auto-detection.
proxy-bypass-list A list of hosts for which proxy settings are bypassed; the specified hosts then use direct connections instead. This flag is ignored unless --proxy-server is also specified. Multiple hosts can be supplied as a comma-separated list.
proxy-server A proxy server that overrides system settings. This flag only affects HTTP and HTTPS requests.
remote-allow-origins Enables web socket connections from the specified origins only. The * wildcard allows any origin.
remote-debugging-port Enables remote debugging over HTTP on the specified port.
RendererAppContainer Enables Renderer AppContainer.
Restart Indicates that Microsoft Edge WebView2 browser process was restarted (such as after a flag change). Use this flag to ignore the launch when recording the Launch.Mode2 metric.
sdsm-state The "Super Duper Secure Mode" state. Valid values: off, basic, balanced, strict.
SharedArrayBuffer If enabled, indicates that a SharedArrayBuffer thread is present.
SpareRendererForSitePerProcess If this flag is enabled, the Edge Webview spare renderer process tries to always have a warm spare renderer process running for the most recently requested BrowserContext. This feature is only consulted in site-per-process mode.
ThirdPartyStoragePartitioning Enables partitioning of third-party storage, such as IndexedDB or CacheStorage, by the top-level site, to reduce fingerprinting.
unsafely-treat-insecure-origin-as-secure Treats given (insecure) origins as secure origins. Multiple origins can be specified, as a comma-separated list. For the definition of secure contexts, see Secure Contexts, including the section Is origin potentially trustworthy?. Example: --unsafely-treat-insecure-origin-as-secure=http://a.test,http://b.test
use-fake-device-for-media-stream Uses a fake device for Media Stream to replace an actual camera and microphone.
use-fake-ui-for-media-stream Bypasses the media stream infobar, by selecting the default device for media streams (such as WebRTC). Works with --use-fake-device-for-media-stream. Prefer using --auto-accept-camera-and-microphone-capture instead, which doesn't interact with screen capture, such as capturing a browser tab.
use-system-proxy-resolver Uses WinHttp to resolve proxies instead of using WebView2's normal proxy resolution logic. This flag is only supported in Windows.
user-agent A string used to override the default user agent with a custom user agent.
user-data-migrated Indicates that this process is the product of a relaunch following migration of user data.
UseBackgroundNativeThreadPool If this is enabled, WebView2 ThreadPoolImpl will use a background ThreadGroup backed by a native thread pool implementation.
UseNativeThreadPool If enabled, WebView2 ThreadPoolImpl uses a foreground ThreadGroup that's backed by a native thread pool implementation.
V8Maglev Enables the Maglev compiler. This only sets the V8 flag when manually overridden; otherwise, it defers to whatever the V8 default is.

See also