Extends the Performance Navigation Timing API NavigationType with 'useragent_launch' to help measure the cold start scenario during page load. This allows a web developer to measure the performance of their application code compared to the cost of browser initialization tasks. This is a pain point for pinned PWAs or WebView apps that will often require a cold start of the user agent.


Despite the variety of performance measurements available through the current API, it's difficult to discern from the NavigationType whether the measurements reflect those of a regular navigation under normal browsing or of one where the browser is in a non-optimal performance state, such as a cold start. A browser launch is one of the most expensive performance scenarios commonly encountered in typical PWA and WebView patterns. Our proposal seeks to create a new value for the NavigationType enum to differentiate this condition from others in measurements of web application performance. Modifying the NavigationType to include state for a user agent launch (i.e. useragent_launch) will enable engineers to determine whether a given measurement is taken from a launch scenario, enabling greater differentiation of application performance from browser performance in scenarios where the browser engine is launched and terminated frequently. Examples include: Electron apps, system WebViews, or other application scenarios where the browser is relatively short-lived or commonly launched from a terminated state.

Status in Chromium


No active development

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.

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Last updated on 2022-05-11