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Web compat analysis tools

When deprecating or changing web-exposed behavior, it's often important to get a clear understanding of the compatibility impact. We have a variety of tools available to you depending on the scenario. This page is designed to help you choose the appropriate tool (in decreasing order of usage). For questions and discussion, e-mail feature-control@chromium.org.

UseCounter

UseCounter is a framework in Blink which is used to record per-page anonymous aggregated metrics on feature usage, often via the [Measure] idl attribute. Results are shown publicly on chromestatus.com (for the dominant milestone per day) . More detailed break-downs are available to Google employees via the Blink.UseCounter.Features histogram using a formula with the PageVisits bucket in the denominator. Internally it's also possible to look at UseCounter by the fraction of users that hit it at least once in a day, and UseCounters hit within Android WebView. In the vast majority of cases, compat tradeoffs are made entirely based on public UseCounter data.

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Often it's useful to find examples of specific coding patterns in order to understand the likely failure modes and formulate migration guidance. Use technical web search engines like nerdydata.com, or for problems in specific libraries, ranking sites like libscore.com.

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The HTTP Archive

A slightly more advanced form of static web search is to use the HTTP Archive, a database of the top 500k websites, updated by a crawl twice a month. See HTTP Archive for web compat decision making for details on using it for compat analysis.

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Microsoft's CSS Usage Data

CSS usage on the web platform is "from a Bing-powered scan" of lots of pages, and measures both CSS properties and values. (Chrome use counters generally don't exist for values.)

Once a deprecation warning has been landed (or made it to stable), it can be extremely informative to search GitHub issues (or other developer help sites like stackoverflow.com) for discussion of the warning generated on the console (eg. by searching for the chromestatus ID present in the warning).

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Most of the popular libraries and frameworks are present on GitHub. Searching for potentially impacted code can be useful in better understanding the risk.

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On-demand crawl

Occasionally it's useful to search top sites for a specific behavior (without landing a UseCounter and waiting for the data to show up in HTTP Archive). For advanced cases like this we can run a custom chromium build on the telemetry cluster to crawl the top 10k (or more) sites and record whatever we like (with a temporary UseCounter). See Using Cluster Telemetry for UseCounter analysis for details.

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