Intent to Experiment: Container Timing

[Chromestatus]

Contact emails

jwilli...@bloomberg.net

Explainer

https://github.com/WICG/container-timing

Specification

https://WICG.github.io/container-timing

Design docs

https://github.com/WICG/container-timing

Summary

The Container Timing API enables monitoring when annotated sections of the DOM are displayed on screen and have finished their initial paint. A developer will have the ability to mark subsections of the DOM with the containertiming attribute (similar to elementtiming for the Element Timing API) and receive performance entries when that section has been painted for the first time. This API will allow developers to measure the timing of various components in their pages.

Blink component

Blink>PerformanceAPIs

Web Feature ID

No information provided

Search tags

performance, container, timing

TAG review

https://github.com/w3ctag/design-reviews/issues/1034

TAG review status

Issues addressed

Goals for experimentation

During this Origin Trial, we are primarily looking to gain insight into: ## The attribute-based instrumentation model - Usage patterns of `containertiming` - Frequency and purpose of `containertiming-ignore` - Number of annotated elements per page ## PerformanceObserver integration - Adoption of PerformanceObserver with container-timing - Whether developers batch-observe or use targeted observation - Whether buffering behavior meets developer expectations ## Entry shape and timing semantics - Whether the exposed timing values align with developer expectations relative to LCP and Element Timing - Whether additional metadata fields are needed - Whether any fields appear unused or redundant ## Edge cases and ergonomics - Nested containers - Dynamically inserted elements - Interaction with visibility changes and layout shifts

Origin Trial documentation link

https://blogs.igalia.com/dape/2026/02/10/container-timing-measuring-web-components-performance

Risks

Interoperability and Compatibility

No information provided

Gecko: Positive (https://github.com/mozilla/standards-positions/issues/1155) Firefox are positive and are working on an implementation: https://phabricator.services.mozilla.com/D279373

WebKit: Neutral (https://github.com/WebKit/standards-positions/issues/442)

Web developers: No signals

Other signals:

Ergonomics

Performance overhead only happens when enabling, any overhead is low because we piggy back on DOM-traversals which are already happening.

Activation

The feature is consistent with other Performance APIs that work on the Performance Timeline. This feature can't be polyfilled properly, there has been an attempt (see Explainer) but that has high resource usage. Today all the documentation lives in the explainer, we will hope to promote this more once it is exposed to the wider development community.

Security

https://github.com/WICG/container-timing/?tab=readme-ov-file#security-and-privacy

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Ongoing technical constraints

None

Debuggability

Container Timing entries can be printed to the developer console from the PerformanceObserver. The attributes are also observable in the Elements Panel. This feature has basic support from DevTools.

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes
This feature is implemented in Blink and isn't subject to any platform specific APIs

Is this feature fully tested by web-platform-tests?

Yes
https://wpt.fyi/results/container-timing/tentative?label=experimental&label=master&aligned

DevTrial instructions

https://github.com/WICG/container-timing?tab=readme-ov-file#chrome-canary-and-chrome-beta

Flag name on about://flags

enable-experimental-web-platform-features

Finch feature name

ContainerTiming

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/382422286

Measurement

https://chromestatus.com/metrics/feature/popularity#V8Element_ContainerTimingIgnore_AttributeGetter https://chromestatus.com/metrics/feature/popularity#V8Element_ContainerTiming_AttributeGetter https://chromestatus.com/metrics/feature/popularity#ContainerTimingObserverRegistered

Estimated milestones

Origin trial desktop first	147
Origin trial desktop last	152
DevTrial on desktop	145
Origin trial Android first	147
Origin trial Android last	152
DevTrial on Android	145
Origin trial WebView first	147
Origin trial WebView last	152

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5110962817073152?gate=5112674898411520

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/672cffcd.2b0a0220.d9f4a.0540.GAE%40google.com

This intent message was generated by Chrome Platform Status.

[Yoav Weiss (@Shopify)]

LGTM to experiment 147 to 152, inclusive 

This is a long-awaited feature, and it was thoroughly discussed in the WebPerfWG

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