Enable experimental flags and source testing for new web APIs in Edge

If you're working with new web APIs and need to stay one step ahead, Microsoft Edge offers several paths to enable features that are not yet in the stable channel. These include DevTools experiments, browser flags, and source testing.In this guide, we've compiled everything into a single resource so you can test safely, compare approaches, and avoid performance or compatibility issues.

In addition to the well-known edge://flags, Edge integrates an Experiments page with checkboxes into its Developer Tools (DevTools) that unlock features in development. And if you need to test with real users in production, there are token-limited source tests in There. We explain how to enable each option, what risks it entails, and when each one is appropriate..

What options do you have to enable experimental features in Edge?

In Edge you can activate features of three complementary forms depending on the scenario. The first, from the Experiments page in DevTools to change the behavior of the tools themselvesThe second, using browser flags in edge://flags to alter the Chromium runtime. And the third, with source tests, to enable a specific API to your site's users with a server token or meta tag.

It is convenient to separate concepts well: Flags and experiments affect your local browserWhile Origin tests enable APIs for your website visitors without asking them to change their configuration. This distinction is key to avoiding mixing flows and choosing the right method for each development phase.

How to enable or disable experiments in DevTools

The DevTools Experiments page provides access to features in development that may change between releases. Only enable them when you need those capabilities for debugging or analysis. and assumes that they may require restarting DevTools.

Quick Steps: Open DevTools by right-clicking on the page and selecting Inspect (or use Ctrl+Shift+I on Windows/Linux, Command+Option+I on macOS). In the DevTools toolbar, go to Settings and choose the Experiments page. Check or uncheck the boxes you need and click Reload DevTools to apply the changes.

Reset Experiments to Default Values

If you notice instability or slowness, you can return to the initial state. Open DevTools, go to Settings and the Preferences page use the Restore Defaults and Update button. When you close DevTools, it will return to the default settings. of the experiments.

Filter and locate experiments in DevTools

To find a specific box, Use the Filter text box within the Experiments pageAs you type, you'll only see options that match that text. Clear the filter to retrieve the full list.

How to send feedback to the Edge DevTools team

Microsoft is seeking specific feedback on these features. If you encounter any issues or have any suggestions, please contact the Edge DevTools team through the official channels.The more detailed the report, the more useful it will be for stabilizing the feature.

List of current experiments in DevTools

The following list summarizes the boxes available in the latest Canary channel and their stable counterparts. As a general rule, they are present in Edge Canary 140 and Edge Stable 138, unless otherwise indicated in each point.

Capture of node creation stacks

Allows Collect JavaScript stack traces when adding nodes to the DOM at runtime. Adds a Stack Trace tab in Elements, next to Styles, to inspect the source of an insert.

Protocol monitor

Activate the tool Protocol monitor to view CDP messages sent and received by DevTools. Open from More Tools or from the Command menu by searching for protocol.

Option to expose internal elements in heap snapshots

Shows a checkbox in the Memory tool to expose internal elements in heap snapshots and facilitate advanced diagnostics.

Vertical drawer configuration

Marked as new since Edge 139. Currently it has no practical effect; to move Quick Look, use its own dock button on the right. Does not appear in Stable 138.

APCA perceptual contrast in the color picker

replaces the old AA/AAA ratios by the APCA algorithm, which calculates contrast based on context, font thickness and size, and environmental conditions.

Full accessibility tree view in Elements

Add a button for switch between the DOM tree and the accessibility tree within the Elements tool, switching the view according to your needs.

New visual font editor in Styles

Enter the Font editor to change units, toggle keywords, convert, and generate exact CSS of typographic properties without leaving the Styles tab.

Automatic contrast reports in the Problems panel

Enable the automatic detection and reporting of contrast problems accessible from the Problems tool, with documentation and resources related to it.

Characteristics of experimental cookies

Allows you to test experimental features related to cookies, useful for validating platform changes before shipping.

Highlight offending node or attribute in the DOM

Underline in the DOM tree the problematic nodes or attributes to speed up the discovery of markup or rule errors.

Group origins into created and deployed trees

In Origins, separate the resources into authoring (created) and production (deployed) folders to differentiate the original code from the packaging.

Hide code from the Skip list in Sources view

Allows hide in the Source tree the code marked for omitting, making navigation between relevant files easier.

Performance: postMessage streams

On the Main track, distinguish events Schedule postMessage and On message, linked with initiator arrows to analyze queues and controllers between threads.

Performance: Experimental Insights Panel

Add Additional information in the Insights side panel. Enable Insights first, then its experimental variant to see even more data.

Console: Log uncaught DevTools exceptions

Check if DevTools internal exceptions are logged in the Console, useful for debugging the tool environment itself.

Enable webhint in Problems

Integra webhint to display accessibility, compatibility, security, performance, and PWA suggestions in the Problems panel, with links to related tools.

Show problems in Elements

Surface contracting wavy underlines in the DOM due to syntax errors detected, with direct access to the explanation of the problem.

Open source files in Visual Studio Code

Replace the Sources code editor with VS Code for local files. When you select a working folder, the links open the file directly in VS Code. and changes are synced live.

Adaptive CPU Throttling

Activate a dynamic CPU throttling strategy for performance testing under different conditions.

CSS Copilot integrated into the sidebar

Allows ask Copilot about HTML elements and CSS rules from Elements. Requires the Edge sidebar to be active.

Dynamic Heap Profile

Live update the heap profile to view memory trends as you interact with the page.

Heap sampler timescale

Show in Performance a Sampling Heap Profiler Timeline to study allocations and withholdings in period.

Performance: Invalidation tracking

Add a section of Recalculate Style Summary Overrides to find out which nodes caused expensive recalculations.

Performance: Show all events

Switch the display of all recorded events in the trace session, useful for thorough investigations.

Performance: V8 runtime call statistics

Displays in the Performance tool the V8 engine internal call metrics, providing time context in JS.

Performance: Improved trace collection v2

Makes Performance Capture new trace types for the enhanced v2 format which is being deployed in Chromium.

Performance: Collecting source text in compiled scripts

When exporting the trace file, includes the source text of the compiled scripts within the trace for offline analysis.

Performance: Trace Event Debug Mode

Add a section in Summary Trace event with name, duration, and debugging information of the selected event.

Instrumentation breakpoints

Improves reliability when stopping at instrumentation breakpoints, facilitating inspections at critical points in the pipeline.

Using scope information from source maps

Allows DevTools use the scope context of source maps to offer debugging that is more faithful to the original code.

Origin Testing: Enable experimental APIs on your site

When you want to test with real users without requiring changes, use source testing. A token temporarily enables an experimental API for your domain in Microsoft Edge., even if the feature is disabled by default in the browser.

Operation: Edge detects the origin token in your HTML or HTTP header and internally sets the experimentation flag for that origin. The user doesn't need to touch edge://flags or install anything.

Registration and obtaining the token

Steps: Go to the Microsoft Edge Origin Testing page, Choose an active test and accept the termsIf prompted, sign in (for example, with GitHub) and complete the form indicating your domain or subdomain.

You can register: a single domain, a specific subdomain, or the domain plus all its subdomains. Paths and parameters are not supported; they are truncated to the root. Upon submission, your token is generated and visible in the Logs section.

How to use the token in production

Insert the token as meta tag in the head or as a response header. Examples: <meta http-equiv='origin-trial' content='EXAMPLE_TOKEN'> the header Origin-Trial: EXAMPLE_TOKEN. To stop participating, remove the meta or header.

Detect features and prepare reservations

Treat tests as experimental. Use feature detection and add fallbacks when the API is unavailable, if the token expires or if the team decides to end the experiment early. See MDN's feature detection guide.

Testing on localhost and expiration

The token mechanism doesn't work on localhost. To develop locally, enable the appropriate flag in edge://flags. Tokens are usually expire after 6 weeks; renew them from the Origin Tests page when appropriate.

Duration and early end

A test may last until its scheduled date or close early for security or design reasonsIf the deadline expires early, the developers will be contacted by email.

Send feedback about your experience

From the testing page, Click the Comments button to open the repository's Issues tab. and document your use case and results. This input is vital for standardization.

Browser Flags: Enable platform features in Edge

Flags are hidden switches in Chromium-based browsers. In Edge, navigate to edge://flags to enable features in development such as web platform APIs or browser behavior changes.

Warning: These options are experimental. It is not recommended to change them in your daily browser.; do this on development channels (Beta, Dev, or Canary) and only when instructed to do so by trusted guidance.

about://, chrome:// and edge://: the trick for any Chromium

All Chromium browsers resolve internal schemas. If you type chrome://flags in Edge, it is rewritten to edge://flagsFor inclusive documentation, use about://flags: each browser rewrites it to its correct schema.

Useful flags and practical examples in Edge

Some Edge-specific flags come in very handy. Below you will see examples that you can enable from edge://flags and illustrate how to work with the section.

Improve text contrast

En Windows, active edge://flags/#edge-enhance-text-contrast to Use system contrast and gamma when rendering fonts, achieving a more homogeneous reading.

Block multimedia autoplay

With edge://flags/#edge-autoplay-user-setting-block-option you enable the option to block autoplay. Then, go to Settings > Cookies & site permissions > Autoplay or go to edge://settings/content/mediaAutoplay.

Navigate back with the Backspace key

the flag edge://flags/#edge-backspace-key-navigate-page-back allow go back with Backspace and forward with Shift+Backspace. It's very useful if you primarily browse with a keyboard.

Tabs with rounded corners

If you prefer a softer look, edge://flags/#edge-visual-rejuv-rounded-tabs round the four corners of the eyelashes and visually separates them from the omnibox.

Smooth PDF Scrolling

Enable edge://flags/#edge-smooth-scrolling-enabled-pdf to smoother scrolling when viewing documents PDF integrated into the browser.

Send content to Chromecast

If the Broadcast option doesn't work, enable these three flags: #load-media-router-component-extension, #global-media-controls-for-cast y #mirroring-serviceAfter a restart, you should be able to send tabs, desktop, or files.

Sleeping tabs to save resources

In the Edge development channels you can enable Sleeping Tabs to Hibernate inactive tabs and reduce RAM usage. Find the option by name, enable it, and adjust the timeout in Settings > System > Save Resources. You can also maintain a whitelist of sites that should not be put to sleep..

Good practices when experimenting

Before touching anything, prepare your environment. Use Edge Canary or Dev for testing, keep stable for daily work and document what you enabled and why. If something goes wrong, you'll know what to revert.

When using source tests, implements feature detection and alternative routesAPIs can change, expire, or be discontinued; your product shouldn't break if they disappear.

Don't ask your users to change browser flags. Marks are intended for development, not production environments.If you need user testing, use source test tokens and segment your deployment.

Lastly, remember that Experimental features may be unstable or unreliableIf performance degrades, disable non-essentials and reset DevTools to defaults when necessary.

Exploring Edge's experimental capabilities allows you to validate new APIs, improve your debugging workflow, and prepare for more robust releases. Between DevTools Experiments, edge://flags flags, and source tests, you have a full range of options. for every stage of development: from local research to controlled testing with real users, always with clear warnings, rollback methods, and guidelines for reporting useful feedback to the Microsoft team and the Chromium community.