Description of indicators
Web Metrics is a new initiative pioneered by Google to provide a unified guide to Web quality signals that are critical to delivering a great user experience on the Web.
Over the years, Google has provided a number of performance measurement and performance tools. Some developers are adept reporting at using these tools, while others find the sheer number of tools and metrics overwhelming.
Site owners do not need to be performance experts to understand the quality of experience they are providing to users. The Web Metrics Program is designed to simplify scenarios and help websites focus on the most important metrics, namely Core Web metrics.
Core Web metrics
Core Web Metrics are a subset of Web metrics that apply to all Web pages, that every website owner should measure, and that will also be displayed in all Google tools. Each core Web metric represents a different aspect of the user experience, can be measured in practice, and reflects the true experience of key user-centric outcomes.
The constituent metrics of the core Web metrics evolve over time. The current composition of metrics for 2020 focuses on the three aspects Loading performance of the user experience, Interactivity and Visual stability, and includes the following metrics (and their corresponding thresholds):
- Largest Contentful Paint (LCP): Maximum content drawing, measuring Load performance. To provide a good user experience, the LCP should occur within days after 2.5 seconds the page first starts loading.
- First Input Delay (FID): First input delay, measured Interactivity. In order to provide a good user experience, the FID of the page should be 100 milliseconds or shorter.
- Cumulative Layout Shift (CLS): Cumulative layout offset, measured Visual stability. In order to provide a good user experience, the CLS of the page should be kept at 0.1 or less.
To ensure that you can achieve the recommended target values during the majority of user visits, a good measurement threshold for each of the above metrics is page-loaded 75th percentile and applies to both mobile and desktop devices.
If a page meets the 75th percentile of the recommended target values for all three metrics above, the tool that evaluates compliance with the core Web metrics should judge the page as passing.
Page performance monitoring
| Metrics | Description | Calculation formula |
|---|---|---|
| FP | First Paint, that is, the time point of first rendering. In performance statistics, the time from the time point when the user starts to access the web page to the time point of FP can be regarded as white screen time, that is, in the process of users accessing web pages, before the FP time point, the user sees a white screen without any content, and the user cannot perceive any effective work in this stage. | - |
| TTFB | Time To First Byte, that is, the time taken for the first byte network request, the time from issuing a page request to receiving the first byte of the response data. | responseStart-fetchStart |
| FCP | First Contentful Paint, that is, the time point when there is first content rendering. In performance statistics, the time from the time point when the user starts to access the web page to the time point of FCP can be regarded as no content time. That is, in the process of users accessing web pages, before the FCP time point, the user sees a screen without any actual content, and the user cannot obtain any useful information at this stage. | - |
| LCP | Largest Contentful Paint is a Core Web Vitals metric that measures when the largest content element in the viewport is visible. It can be used to determine when the main content of the page has finished rendering on the screen. | - |
| CLS | Cumulative Layout Shift is a measure of the maximum layout change score for each unexpected layout change that occurred over the life of the page. | - |
| FID | First Input Delay is a measure of the delay from the first time a user interacts with a page to the time when the browser can actually start processing event handlers in response to that interaction. | - |
| TTI | Time to Interactive is a non-standardized web performance "progress" metric defined as the point in time when the last "longtask" is completed, followed by 5 seconds of network and main thread inactivity. | - |
| TBT | Total Blocking Time is a metric that measures the total time between FCP and TTI, during which the main thread was blocked for too long to respond to input. | - |
| LoadEventEnd | Loading event ends. | loadEventEnd-fetchStart |
| Fully loaded | After DCL is completed, it will monitor the asynchronous requests initiated within a period of time (default 500ms) and monitor the time it takes to fully load. It can be considered as the time it takes to fully load the page. | - |
| DCL | DOMContentLoaded measures the point in time when the browser is ready to execute any client-side scripts. DCL (Document Content Loaded) occurs during the web page loading process when the browser has assembled the DOM (Document Object Model) and there are no stylesheets preventing the execution of JavaScript. | - |
| Redirect | If redirection does not occur, or one of the redirects is not from the same origin, the value is 0. | redirectEnd - redirectStart |
| DNS | Domain name resolution time (0 when hitting the resolution cache). | domainLookupEnd - domainLookupStart |
| TCP | TCP connection time. | connectEnd - connectStart |
| SSL | SSL secure connection time. | connectEnd - secureConnectionStart |
| Request | The time it takes to send the first response from the client to the server after the SSL connection is established. | responseStart - requestStart |
| Response | The time it takes from the first response from the server to the complete response of the data. | responseEnd - responseStart |
Page analysis indicators
| Indicator | Description | Calculation formula |
|---|---|---|
| Number of slow pages | Page visits exceeding the slow page threshold. | Page visits exceeding the slow FCP threshold + exceeding the slow LCP threshold + exceeding the slow DCL threshold + exceeding the slow full load threshold |
| Slow page ratio | The ratio of page visits exceeding the slow page threshold to the total visits. | (Page visits exceeding the slow threshold (slow FCP, slow LCP, slow DCL, slow full load) / total visits) * 100% |
| Number of users affected by slow pages | UVs with slow pages | - |
Operation analysis indicators
| Indicator | Description | Calculation formula |
|---|---|---|
| Number of operations | The number of times an operation is requested. | An operation is requested once and recorded once. |
| Operation time | The time when the operation is completed. | When the operation is an Ajax request, the end time of the last Ajax of the multiple Ajaxs corresponding to the operation - the start time of the first Ajax. When the operation is a page, the completion time of the FCP/LCP/DCL/full load indicators of the user-defined page is the operation time. |
| Operation availability | The ratio of successful operations to the total number of operations. | (Successful operations/Total operations)*100% |
| Operation request time | The projection time of the request corresponding to the operation. | - |
| Average server time | The time from the server receiving the request to the completion of processing. | - |
User analysis indicators
| Indicator | Description |
|---|---|
| PV | Page View, page visits. |
| UV | User View, user visits. |
| Session | User session visits, from entering the page to closing the page as a session. |
JS error indicators
| Indicator | Description |
|---|---|
| Number of JS errors | Number of PVs with JS errors |
| JS error rate | Number of PVs with JS errors/Total PV |
| Number of users affected | Number of UVs with JS errors |
Request analysis indicators
| Indicator | Description |
|---|---|
| Response time | Time from when a request is issued to when the server returns and receives the returned result |
| Number of requests | Number of requests to access the application |
| Slow request ratio | Number of requests exceeding the slow request threshold/Total number of requests reported |
| Number of users affected by slow requests | UVs with slow requests |
| Error rate | Number of requests with status code 400 or above/Number of requests |
| Number of users affected by errors | Number of UVs with request errors |