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Launching Features

If you have concerns about your feature not fitting into this process, or any other questions, general concerns or discussion on this page or the process it describes, please e-mail blink-api-owners-discuss@chromium.org.

Exempt features

You do not need to use this process if your change is not exposed to web developers. This means:

The rest of this document doesn’t apply to these types of changes, although such features might still have to go through a different launch process. Large projects should have public design docs that are also shared on blink-dev@chromium.org (or chromium-dev@, for projects that have significant parts outside of Blink) for feedback (this is also a good way to get the attention of other relevant leads).

Frequently asked questions

Q: Do I need any of this if my project is just refactoring or re-architecting the code? Do the API owners need to be involved?

A: No. The API owners oversee the process of shipping web-exposed API changes. They are not necessarily leads or overseers of any of the code. Instead, you should get the buy-in of the leads of the code areas touched by your project. If there may be side effects of your change, you should follow the "Architectural change" process below. In addition, such large projects should have public design docs that are also shared on blink-dev@chromium.org (or chromium-dev@chromium.org, for projects that have significant parts outside of third_party/blink) for feedback (this is also a good way to get the attention of relevant leads you might not have thought of).

For code-related questions, you can email platform-architecture-dev@chromium.org in addition to blink-dev@ as a catch-all option when the code ownership is not clear or the feature needs large-scale refactoring changes.

Q: What if I want to add some code to third_party/blink that is for a non-web-exposed feature? Is that allowed?

A: In general, no. On a case-by-case basis an exception could be given if there is no other reasonable way to implement the feature. Ask for permission from leads of the code area as well as the API owners. (The API owners need to be involved only to help understand if the feature really is not web-exposed; this can be a very subtle question.)

Q: I am not sure of the right approach for my feature. What should I do?

A: Please reach out to the API owners for help! While they are not gatekeepers for everything, they are very happy to give advice and unblock your feature. An email to blink-api-owners-discuss@chromium.org is the best way; if a public-facing email is not possible, please email the API owners directly.

Q: Do I need tooling support for my new feature?*

Shipping new Web Platform features in Chromium requires tooling support. Follow the DevTools support checklist to figure out the appropriate steps to take for your feature.

Q: What if another browser or the W3C TAG objects to my new feature? Can I ship it anyway?

A: Blink and Chromium do sometimes ship features over the objections of other browsers or the TAG, though we prefer to build consensus around features if possible. See the Blink Values in Practice for how we make this tradeoff.

The Feature Types

The first thing you will need to do is identify what type of feature you are building:

New feature incubation

This is the normal path when we are incubating and defining new features from scratch - e.g., most Fugu features follow this pattern, and any feature where we start without an already-defined standard for the feature. This also covers changes that are extending existing features (e.g., defining a new value and behavior for an existing standard feature). This type of feature has the most associated process steps, as it is charting new territory.

Implementation of existing standard

This type of feature has a lighter-weight “fast track” process, but this process can only be used when the feature has already been defined in a consensus standards document - e.g. a W3C Working Group has already agreed on the design, it has already been merged into a WHATWG standard, or the feature has already been implemented in another engine.

Deprecation

Removal of already-shipped features.

Web developer facing change to existing code

This type is not commonly used. It is basically a public service announcement- “This is a web-developer-facing change to existing code without API changes, but you may see side effects.” This may be due to large-scale code refactoring or rewriting, where the goal is to cause no behavioral changes (but due to scope of change, side effects are likely), or this may encompass changes to current code that fix a bug or implement new changes to the spec without changes to the API shape itself.

Changing feature type

It is possible to change types later in the process - for example, if you start out implementing an already existing standard, but discover you need to incubate a new API during the process, you can start over with a new ChromeStatus entry. Note that there are few strictly required gates to the Chromium process (e.g., 3 LGTMs from API owners on an intent-to-ship) - particularly in the earlier stages we want to encourage experimentation. However, there are required fields for most stages in the ChromeStatus tool, and it’s important to consider all the steps listed below; this will maximize your chance of success on an intent-to-ship and reduce the risk of having to redo parts of your design or implementation.

The Chromium process to launch a new feature

Step 0: Create a ChromeStatus entry, and choose your feature type.

For all types of features, the first step is to create a ChromeStatus entry. Go to https://www.chromestatus.com/features, ensure you are logged in (see the upper right corner), and click “Add new feature”. If you do no have access to create a new feature, please send an email to webstatus-request@google.com to request access. Follow the directions to name your feature and give a short summary, and select the appropriate feature type.

For Chrome, some launches will require a formal Chrome launch review (especially if your feature has security, privacy, legal, or UI implications). You can work with a Google counterpart to get all launch approvals. We are working on making this process more open and transparent outside Google (new tooling is in progress).

From this point on, the process changes a little depending on the type of feature you’re adding.

For New Feature Incubations

Step 1: Incubating: Write up use cases and scenarios in an explainer

Proceed to the "Start Incubating" stage in ChromeStatus.

Write up the use cases and scenarios for the feature in an explainer, which is typically written in Markdown. Then host your explainer at a public URL. Some organizations recommend specific places:

Otherwise, a public personal Github repo typically works well. Then put a link to your public explainer in the feature entry.

We have a program for to provide mentorship for specification writing; If you are a Googler you must file a request for a spec mentor, and ask them to review this early explainer before proceeding. If you are not a Googler, you are welcome to make use of this but not required to.

Then kick off "standards incubation" by proposing your explainer to a relevant incubation venue or working group and socializing the problem with other vendors and developers. For web features, the WICG is a good default, but ask your spec mentor if you need help picking a venue. Enter a reference to the public proposal in “Initial Public Proposal” field. It’s also a good idea to discuss your idea with the team/team lead (TL) or area expert in the feature area, prior to checking in code in the area.

After some discussion with the community, start sketching out a proposed solution in your (public) explainer, including sample code for using your API design. You may wish to review this with your specification mentor before proceeding to prototyping.

Step 2: Prototyping

Proceed to the “Start Prototyping” stage in ChromeStatus - this will generate an “Intent to Prototype” mail for you. Send that email to blink-dev and start checking in prototype code to Chromium under a runtime flag. You should do your detailed API design in the open, in your public repository, and response to feedback filed there. You should continue pushing for public engagement (from other vendors and web developers), and to move into an incubation venue or working group if you haven’t already. During this stage, you should expand on the explainer with a full design doc (this may also have implementation-specific details), and consider creating a specification (or writing up a pull request with changes to an existing spec).

Note that any CLs landing at this stage should be behind a feature flag. Consider adding a UseCounter to track usage of your new feature in the wild, and be sure to write integration tests for your feature as web-platform-tests as you go. Continue to work with your API mentor if there are any design changes.

Ensure you have an API overview and descriptions for all IDL methods and properties (these are probably in your specification or explainer, but developers will need them to try your feature out), and at least a basic sample.

As soon as you have a functional and reasonably complete implementation of your initial design ready for developers to try out behind a flag, proceed to the next step.

Step 3: Feature Complete behind a feature flag: iteration on design

Once you have a functional and reasonably complete feature implementation available as a runtime enabled feature, we recommend (but don't require) that you request an Early Design Review from the TAG and proceed to the “Dev Trials” stage in ChromeStatus (note also exceptions enumerated here). This will generate a “Ready for Developer Testing” email that you should send to blink-dev to notify the community they can try out the feature. At this point, you should consider asking other browser vendors and the web developer community for signals on their opinion of the API.

This is the main iterating stage of feature development and helps you assess product-market-fit early on before you corner yourself (does your API address a problem with meaningful demand? did we get the ergonomics right?). You may wish to send more than one Ready for Developer Testing emails, if you make substantial changes to the API shape while iterating. You should work with the TAG to complete their review and address any issues raised during this stage, and should address any issues raised by other horizontal reviews (accessibility, privacy, internationalization, etc.).

Flag guidelines require you to place the code change behind a flag, which enables a quick roll-back of that change in situations where we find our estimate regarding its breaking potential was overly optimistic.

Step 4: Widen review

Once you believe you have addressed all major open issues, you should proceed to the “Evaluating readiness to ship” stage in ChromeStatus.

By this point, your explainer and other public specification work should have migrated to an incubation venue (or a full working group), in order to assure contributors that IP concerns are being handled appropriately, and so that all browser vendors are able to provide structured feedback in a known place. Any W3C community group is acceptable, as is publication as an IETF internet draft. For web features, the WICG is a good default, but ask your spec mentor if you need help picking a venue. If migrating the work to a CG is not appropriate for your case (e.g. you're running an experiment you're not intending to ship as is), you can ask for an exception from the API owners.

If you haven't already received signals on their opinion of the API from other browser vendors and the web developer community, now is the time to pursue getting those signals.

You should also work with the documentation team to ensure your features will be documented when shipped, and estimate when (in what milestone) you would like to target shipping.

You should also decide if an Origin Trial would help gather significant data for your feature.

Now that you think your overall design is relatively settled (or just after starting your Origin Trial), if you haven't already, start writing your specification. Talk to your spec mentor about how long you should expect this to take. As a very rough guess, estimate at least a month of full-time work, but that can take more calendar time than the 12-16 weeks of an Origin Trial. Starting the spec-writing process too late might delay your feature launch.

Once you have a complete specification:

  1. If you have one, ask your spec mentor to review the specification.
  2. Request a Specification Review from the TAG (except in the cases noted here). You should submit this at least a month ahead of sending an Intent to Ship, to give the TAG sufficient time for meaningful feedback.

Step 5 (Optional): Origin Trial

If you want to gather data on the usability of your feature that an Origin Trial can help collect, proceed to the “Origin Trial” stage in ChromeStatus and fill out the required fields detailing what you hope to learn from the origin trial. This will generate an Intent to Experiment mail that you should send to blink-dev. After receiving at least one LGTM from the API owners, you can proceed with your origin trial release. Collect data and respond to any issues. From here, you may wish to return to Dev Trials, proceed to Prepare to Ship, or park the feature.

As noted above, a specification is recommended but not required for an Origin Trial.

Please note that Origin Trials are not exempt from requiring cross-functional approvals from the Chrome launch review process.

Depending on your feature and your experimentation goals, running an experiment via Finch on a percentage of the stable or beta populations may be useful (example). In these cases, an Intent to Experiment explaining why this non-typical path is requested and the corresponding LGTM(s) are still required before proceeding.

An initial origin trial for a feature may only run for 6 milestones of Chromium. Each request to extend beyond that limit may only be for 3 milestones at a time, and will not be approved unless substantial progress is demonstrated in all of these areas:

Each subsequent request to extend an origin trial must provide substantial additional progress on top of the previous extension request.

Technical note: Origin Trials are nowadays "gapless", which means they are configured to end after the version of Chrome with the feature enabled by default is available to most users. The current convention for that is that the trial ends when the Chrome milestone after the one where the feature is enabled by default ships. This technicality will only be relevant to you if you intend to pause the experiment after the trial is over and restart it later, e.g. for very early stage experiments where there is certainty that they will be revised before shipping. In such cases you can enforce a break in the trial to demonstrate lack of usage before restarting the experiment. Email origin-trials-support@google.com to discuss this option.

Step 6: Prepare to Ship

By this stage, you need to have a complete specification available that matches what you have implemented, and you should have given the TAG at least a month to comment on that specification. If you are a Googler you should get a final spec review from your spec mentor, and discuss options for moving your spec to a final standardization venue. You should get final signoff from Documentation.

If the TAG has commented on your review, and the state of the review is anything other than Resolution: satisfied, the API Owners should be able to see evidence that you've seriously and comprehensively engaged with their comments, and tried to resolve any concerns.

If your specification is still in an incubation venue and not a working group, propose that the feature migrate to a working group. There's no requirement that a working group adopt the feature before Chromium ships it, but if we're ready to ship it, we need to declare publicly that we think incubation is finished. Ask your spec mentor for help with this.

If your specification has more than a handful of open issues, consider labelling those issues such that it is clear which of them are editorial, which are asking for future enhancements, and which would require breaking changes that may pose a compatibility risk. If you don't already have appropriate labels, consider using editorial, enhancement, and compatibility-risk

Update ChromeStatus with:

Proceed to the “Prepare to Ship” stage in ChromeStatus; this will generate an "Intent to Ship" mail that you should send to blink-dev. If your specification isn't a modification of an existing specification, include a one-line spec maturity summary from someone outside your team (like your spec mentor) who has done a review. This will spark a conversation with the API owners; address any feedback from them, and once you get 3 LGTMs from the API owners, you may enable the feature by default. You can learn more about the policies and guidelines the API owners evaluate here. Requirements for new API owners are here. Email blink-api-owners-discuss@chromium.org or reach out to one of the API owners if there is no open/unaddressed feedback and you are still blocked on LGTMs after 5 days.

Once you have the needed approvals, set the implementation status to "Enabled by default" in ChromeStatus. You will likely also need to land a Chromium CL to turn on the feature. Link to the blink-dev thread via the Google Groups web interface in your CL's commit message to make it easy and clear to review.

Implementations of already-defined consensus-based standards

Step 1: Write up use cases and scenarios, start coding

Fill out the “Motivation” section with a brief summary, and then write up the use cases and scenarios. If this is a large feature, or a combination of multiple attributes/properties/methods/events, you may wish to do this in a separate explainer file.

Proceed to the “Start Prototyping” stage in ChromeStatus - this will generate an “Intent to Prototype” mail for you. Send that email to blink-dev and start checking in prototype code to Chromium as runtime enabled features. Ensure there are adequate web-platform-tests for this feature. Also ensure you have an API overview and descriptions for all IDL methods and properties (this is probably already in the consensus standard specification, or even on MDN), and at least a basic sample.

As soon as you have a functional and reasonably complete implementation of the feature ready for developers to try out under a flag, proceed to the next step.

Step 2: Feature Complete behind a flag and implementation refinement

If the TAG has not already reviewed the consensus specification, request a Specification Review (except in the cases noted here) and proceed to the “Dev Trials” stage in ChromeStatus. This will generate a “Ready for Developer Testing” email that you should send to blink-dev to notify the community they can try out the feature.

After you have addressed any issues that the community finds, you should proceed to the “Evaluating readiness to ship” stage in ChromeStatus. You should also work with the documentation team to ensure your feature will be documented when shipped, and estimate when (in what milestone) you would like to target shipping. You should also decide if an Origin Trial would help gather significant data for your feature.

Step 3 (Optional): Origin Trial

The Origin Trial guidelines for new feature incubations applies here as well.

Step 4: Prepare to Ship

You should update ChromeStatus with a target milestone for shipping (and remember to keep this updated, if things change). If you are working with DevRel on documentation, this is the time to finish that work and update for any changes in vendor signals.

Proceed to the “Prepare to Ship” stage in ChromeStatus; this will generate an Intent to Ship mail that you should send to blink-dev. This will spark a conversation with the API owners; address any feedback from them, and once you get 3 LGTMs from the API owners, you may enable the feature by default. See here for the principles the API owners will apply in evaluating whether the feature is mature enough to ship. (API owners requirements are listed here - email blink-api-owners-discuss@chromium.org or reach out to one of the API owners if no open/unaddressed feedback and you are still blocked on LGTMs after 5 days.)

Once you have the needed approvals, set the implementation status to "Enabled by default" in ChromeStatus. You will likely also need to land a Chromium CL to turn on the feature. Link to the blink-dev thread via the Google Groups web interface in your CL's commit message to make it easy and clear to review.

Feature deprecations

Deprecating/removing features creates a heavy burden for developers and users. Broken sites might hurt developers’ livelihood or prevent users from completing vital tasks. Ambiguous removal timelines confuse developers and make it hard for them to respond appropriately.

Deprecations and removals must have strong reasons, explicitly balanced against the cost of removal. Deprecations should be clear and actionable for developers. When suggesting a deprecation/removal, be ready to answer these questions:

High-usage APIs may require much more work to land successfully. See here for a good example of how this worked in practice with the deprecation and removal of the Web Components v0 APIs.

Step 1: Measure usage

Measure feature usage in the wild. Various tools are available, but typically this is accomplished by adding your feature to the UseCounter::Feature enum and adding MeasureAs=<your enum value> to the feature's IDL definition.

It takes 5-9 weeks (based on 2023's typical 4-week release cycle) to hit Stable once you enable instrumentation. If there is time pressure you may be able to get permission to merge UseCounter changes into an existing dev/beta branch, and make provisional decisions based on data from beta channel.

Step 2: Coordinate with other engines

If multiple browser engines support the feature, talk to decision-makers at the other engines and to spec editors in order to ensure that the feature is removed in a coordinated way. We usually don't want to try to remove a feature from Chromium if Gecko and WebKit are going to keep supporting it. Once you have a coordinated removal plan, file standards position issues to document the agreement.

Step 3: Deprecate the feature

Proceed to the “Write Up Motivation” stage in ChromeStatus.

Fill out the “Motivation” section with an explanation of why you want to remove this feature and why you think you'll be able to remove it. Make sure to provide suggested alternatives to the feature being deprecated.

Consider whether your feature is likely to need a deprecation trial, and if so, describe what you know about the deprecation trial. You'll be able to correct this later if you learn something new.

Also describe the conditions under which you plan to proceed to removing the feature. For example, you might expect that just running dev trials for several milestones will be enough, or you might only want to remove if measured usage drops to a certain level. Again, you'll be able to change your mind later by sending another email and waiting for the API owners to agree to it.

Have ChromeStatus generate an “Intent to Deprecate and Remove” mail for you, send it to blink-dev, and wait for 3 LGTMs.

Once the API owners have given 3 LGTMs for your removal plan, start checking in your code to add a runtime enabled feature that turns off the deprecated feature. As soon as you have a functional removal of the feature ready for developers to try out under a flag, proceed to the next step.

Deprecating without removal

If you are unsure of when a feature could be removed, or would like to discourage usage, you may deprecate a feature without a removal deadline. This is strongly discouraged and will require significant justification:

Step 4: Dev trial of deprecation

Proceed to the “Dev Trial of deprecation” stage in ChromeStatus. This will generate a “Ready for Developer Testing” email that you should send to blink-dev to notify the community they can try out the feature deprecation.

At this point, you should also notify developers by adding a deprecation issue as outlined here. Give developers as many milestones as possible to respond to the deprecation.

You should work with the documentation team to ensure the community is prepared for this feature deprecation, and estimate when (in what milestone) you would like to target shipping. You should also decide (possibly based on data from the dev trial) if a deprecation trial is going to be necessary to help smooth the removal of this feature from the web platform.

Step 5 (Optional): Deprecation Trial

If you are concerned that there are going to be web developers who need additional time to fix up their implementations, and will want to delay your feature deprecation, you can file for a Deprecation Trial. This will let you disable the feature by default, but let developers request an origin trial token to re-enable the feature, for a limited period of time after the feature deprecation. You will need to decide how long to keep the deprecation trial open and enter that milestone in the tool for planning purposes.

Deprecation trials are especially useful to support enterprise users, who have additional difficulties reacting to breaking changes. See shipping changes that are enterprise-friendly for best practices.

If the details are different from what you wrote in your “Intent to Deprecate and Remove” thread, select “Draft Request for Deprecation Trial email” in ChromeStatus, and send the resulting “Request for Deprecation Trial” email to blink-dev. If the original details were correct, the “Intent to Deprecate and Remove” thread is sufficient.

After your deprecation trial plan has received at least one LGTM from the API owners, request a new trial at ChromeStatus by clicking the "Request Trial Creation" button in the Origin Trial section. Ensure your removal is integrated with the origin trials framework (see details). Once your Deprecation Trial is in place, proceed to the next step.

Deprecation trials are run for up to 6 chromium milestones, and can be repeatedly extended for 6 milestones as long as significant progress is demonstrated in at least one of the following areas:

If significant progress cannot be demonstrated towards removing the need for the deprecation trial, it will be necessary to un-deprecate the API to acknowledge the reality that ongoing support for the API is required for web compatibility.

Step 6: Prepare to Ship

You should update ChromeStatus with a target milestone for disabling the feature (and remember to keep this updated, if things change). You should get final signoff from the Documentation team.

Proceed to the “Prepare to Ship” stage in ChromeStatus. If any details have changed from what you described in your “Intent to Deprecate and Remove” thread, update that thread with the new details, and wait for 3 API owners to confirm that their LGTMs still apply. Otherwise, you can keep following your approved plan without new LGTMs.

You will likely also need to land a Chromium CL to turn on the feature. Link to the blink-dev thread via the Google Groups web interface in your CL's commit message to make it easy and clear to review.

Step 7: Disable the feature

Disable the feature by default. Update ChromeStatus to either “Disabled” or “Disabled with Deprecation Trial”.

Step 8: Wait for the removal to land

If you are running a Deprecation Trial, wait until the Deprecation Trial period has ended.

Monitor developer chatter and bug reports for at least a month or two after your removal has gotten to Stable and any Deprecation Trial has ended to make sure it's landing well. If the removal goes particularly badly, you may need to turn the feature back on using the runtime enabled feature you added above.

If you need to extend the Deprecation Trial, notify origin-trials-support@google.com, click “Generate an Intent to Extend Deprecation Trial” in ChromeStatus, and send the resulting notification to blink-dev. Then repeat this step.

Step 9: Remove Code

Once it's clear that developers are no longer relying on the disabled feature, remove the code, and set the ChromeStatus to “Removed.”

Web-developer-facing change to existing behavior

Before you begin: Assess backwards compatibility

Before choosing this feature type, you should determine if the behavior change you're trying to make can be considered a low-risk bug fix, or it has non-negligible likelihood to result in site breakage.

The following criteria are worthwhile to consider:

After considering these factors, choose the "New feature incubation" or "Existing feature implementation" feature types for any change with some potential to break sites. Use "Web developer facing code change" only for changes deemed very unlikely to break sites, and that change APIs in at most a trivial way.

Another reason for a PSA could be a large-scale refactoring that doesn't intend to result in behavior changes, but may do so in practice.

The purpose of a PSA is to notify the broader Chromium community about the change, and enables folks to test against it and potentially re-examine the risk assessment regarding potential breakage.

Step 1: Write up motivation

Fill out the “Motivation” section in ChromeStatus with a brief summary of the reasons we want to modify the current behavior.

Step 2: (Optional) Dev trial

If you want developers to try out this change before shipping it (e.g., to assess potential breakage), put the relevant code behind a runtime enabled feature, and set the status to “Dev Trial” in ChromeStatus. This will generate a “Ready for Developer Testing” email that you should send to blink-dev to notify the community they can try out this change.

Step 3: Prepare to Ship

You should update ChromeStatus with a target milestone for shipping (and remember to keep this updated, if things change). Proceed to the “Prepare to Ship” stage in ChromeStatus; this will generate a “Web-Facing Change PSA” mail for you. Send that email to blink-dev with the summary of the code change and the expected milestone.

For a PSA you're expected to follow the flag guarding guidelines, which generally allow for some discretion for trivial changes.

You will likely also need to land a Chromium CL to turn on the feature. Link to the blink-dev thread via the Google Groups web interface in your CL's commit message to make it easy and clear to review.

You may wish to use Finch to increase confidence in the new code as you deploy it.

Post Launch

After launching a new feature, watch for crashes, regressions caused by your feature and any substantive spec feedback. Review UseCounter and other metrics. Update the intent-to-ship thread and ChromeStatus if non-trivial issues (like web compatibility or serious design questions) arise. When in doubt, email blink-dev@ (or blink-api-owners-discuss@ if you prefer a smaller audience) for advice.

Once a new API is on by default, continue to support other implementations (for instance, clarifying the spec, improving the tests, fixing bugs, and updating support status in ChromeStatus) until the feature is broadly supported and works the same across engines. Remember, your job is to move the web forward, not simply add features to Chrome.

Review MDN docs for technical accuracy and clarity. Feel free to make edits directly or reach out to jmedley@.

When you are convinced enabling the feature by default has “stuck” (typically 2 milestones), remove any unused code including RuntimeEnabledFeatures entries.

For an overview, and explanation of motivations, please see: