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Explainer https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/PerformanceNavigationTiming%20for%20User%20Agent%20Launch/explainer.md Specification https://w3c.github.io/navigation-timing/#sec-performance-timing-confidence Design docs https://docs.google.com/document/d/1D6DqptsCEd3wPRsZ0q1iwVBAXXmhxZuLV-KKFI0ptCg/edit#heading=h.7nki9mck5t64 Summary Web applications may suffer from bimodal distribution in page load performance due to factors outside of the application's control. For example, when a user agent first launches in a “cold start” scenario, it must perform many expensive initialization tasks that compete for system resources. Browser extensions can also affect performance, since some extensions run additional code on every page you visit, increasing CPU usage and slowing response times. Likewise, when a machine is already busy with intensive tasks, web pages may load more slowly as a result. In these scenarios, content the web app attempts to load will be in competition with other work happening on the system. This makes it difficult to detect if performance issues exist within web applications themselves, or because of external factors. Teams we have worked with have been surprised at the difference between real-world dashboard metrics and what they observe in page profiling tools. Without more information, it is challenging for developers to understand if (and when) their applications may be misbehaving or are simply being loaded in a contended period. A new 'confidence' field on the PerformanceNavigationTiming object will enable developers to discern if the navigation timings are representative for their web application. Blink component Blink>PerformanceAPIs>NavigationTiming Web Feature ID Missing feature Motivation When a user agent first launches (a "cold start" scenario), it must perform many expensive initialization tasks that compete for resources on the system. Consequently, web applications may suffer from bimodal distribution in page load performance. Content they attempt to load will be in competition with other initialization work. This makes it difficult to detect if performance issues exist within web applications themselves, or because of a user-agent-generated condition of high resource contention. This is particularly a pain point for pinned PWAs (Progressive Web Apps) that will often require a cold start of the user agent, and teams we have worked with have been surprised at the difference between real-world dashboard metrics and what they observe in page profiling tools. Without more information, it is challenging for developers to understand if (and when) their applications may be misbehaving or are simply being loaded in a contended period. To address this, we propose adding new information to existing Web Performance APIs. Initial public proposal https://discourse.wicg.io/t/proposal-user-agent-launch-type-in-performancenavigationtiming/5875 TAG review https://github.com/w3ctag/design-reviews/issues/878 TAG review status Issues addressed Origin Trial Name PerformanceNavigationTiming confidence Chromium Trial Name PerformanceNavigationTimingConfidence Origin Trial documentation link https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/PerformanceNavigationTiming%20for%20User%20Agent%20Launch/explainer.md WebFeature UseCounter name kPerformanceNavigationTimingConfidence Risks Interoperability and Compatibility None. Gecko: No signal (https://github.com/mozilla/standards-positions/issues/1191) WebKit: No signal (https://github.com/WebKit/standards-positions/issues/469) Web developers: Positive (https://issues.chromium.org/issues/40255844#comment10) Positive feedback from WebPerfWG. https://w3c.github.io/web-performance/meetings/2025/2025-11-TPAC/index.html#h.jgi0mlvusons Other signals: 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 Debuggability No information provided Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)? Yes Is this feature fully tested by web-platform-tests? Yes third_party/blink/web_tests/http/tests/misc/performance-navigation-timing-entry-confidence.tentative.html Flag name on about://flags No information provided Finch feature name PerformanceNavigationTimingConfidence Rollout plan Will ship enabled for all users Requires code in //chrome? True Tracking bug https://bugs.chromium.org/p/chromium/issues/detail?id=1413848 Estimated milestones Shipping on desktop 145 Origin trial desktop first 136 Origin trial desktop last 139 Origin trial extension 1 end milestone 142 DevTrial on desktop 135 Shipping on Android 145 Origin trial Android first 136 Origin trial Android last 139 DevTrial on Android 135 Shipping on WebView 145 Anticipated spec changes Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (eg links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (eg, changing to naming or structure of the API in a non-backward-compatible way). No information provided Link to entry on the Chrome Platform Status https://chromestatus.com/feature/5186950448283648?gate=6507865714458624 Links to previous Intent discussions Intent to Prototype: https://groups.google.com/a/chromium.org/g/blink-dev/c/o0F7nBKsgg0/m/bJSp3ekfAAAJ Intent to Experiment: https://groups.google.com/a/chromium.org/g/blink-dev/c/FYsfp0OsMko/m/WbhUrqSqAQAJ Intent to Extend Experiment 1: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6091e78f-7c77-4ed3-9559-eb660a14dfb7n%40chromium.org This intent message was generated by Chrome Platform Status. -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6939c150.710a0220.1d2509.07c8.GAE%40google.com.
