We explain what CrUX data is and why any website owner should care about it.
Overview
Web performance metrics can be broadly classified into two distinct groups:
- Lab/Synthetic data
How your page performed under a specific set of repeatable conditions- For example, in Vancouver, Canada on an Laptop with a Fast Broadband connection.
- Essentially what the GTmetrix Report provides you.
- Field/Real user data
How your page performed overall in the real world- Comprises of aggregation of real user data.
- Uses a variety of locations, devices, connection speeds, etc.
- Essentially what PageSpeed Insights (PSI) provides you.
GTmetrix now provides field/real user data through CrUX data – Google’s Chrome User Experience (CrUX) Report, alongside our lab/synthetic metrics.
CrUX data provides an additional perspective on your website’s performance, offering insights that are directly tied to real user experiences.
We’ve covered the key differences between field data and lab (synthetic) data in a prior article, and in this one, we explain what CrUX is, how it works, and why it is an important dataset for understanding and improving your website’s performance.
What is CrUX and How Does it Work?
In a nutshell, CrUX represents anonymized real-user performance data collected from millions of Chrome users. It is the key source for the field data you see not just in the GTmetrix Report but other web performance tools like Google’s Search Console (Core Web Vitals Report) and PageSpeed Insights.
This data focuses on performance metrics that reflect the actual conditions visitors encounter when visiting a website.
Unlike lab data where the environment can be specified and/or controlled, CrUX data simply reflects real-world performance seen across a variety of scenarios.
In other words:
CrUX (field) data tells you how your page performed overall in the real world based on real user experiences, based on a snapshot (or subset) taken across an aggregate of all real user locations, devices, connection speeds, etc.
What is in the CrUX Dataset?
CrUX primarily focuses on these 5 performance metrics that measure critical aspects of the page experience, including:
- Largest Contentful Paint (LCP): Measures loading performance
- Interaction to Next Paint (INP): Measures responsiveness (Replaces Total Blocking Time)
- Cumulative Layout Shift (CLS): Measures visual stability
- Time to First Byte (TTFB): Measures initial server response
- First Contentful Paint (FCP): Measures initial loading performance
LCP, INP, and CLS are part of the Web Vitals set, which Google considers to be the most critical metrics to optimize.
With the exception of INP, which is a field-only metric; all the other metrics can also be measured in the lab.
Difference Between Page and Origin
Within the CrUX dataset, you’ll notice that data is provided for 2 distinct groups – Page and Origin.
- Page refers to a specific page/URL that you’re testing
- For example, https://example.com/landing-page
- For example, https://example.com/landing-page
- Origin refers to domain on which different pages reside on and have the same protocol
- For example:
https://example.com/landing-page
https://example.com/product
https://example.com/categories
…would all have the Origin https://example.com
- However, http://example.com/landing-page-1/ would not be part of the same Origin (its protocol is http:// not https://)
- For example:
Origin essentially represents the entire website i.e., all pages for the specific protocol/domain combination (as explained above), so CrUX provides the aggregate data here.
That means the Origin data is an average of every page on your website that is included in the CrUX dataset.
How Does Google Decide CrUX Eligibility?
CrUX data is collected from eligible Chrome users for eligible websites.
What this means is not all websites (or pages) or Chrome users automatically qualify for inclusion in the CrUX dataset.
We’ve created a table below to explain which users and origins/pages Google considers to be “eligible for inclusion” in the CrUX dataset.
| User Eligibility Criteria | Origin/Page Eligibility Criteria | Has opted into usage statistics reporting By default, if a user signs in to Chrome, this option is enabled. |
Is publicly discoverable If your site (or page) does not return a 200 OK (after redirects) or explicitly instructs search engines not to list it, the site (or page) is excluded from the CrUX dataset. |
| Has not disabled sync Users who log into Chrome must enable this option, otherwise they are excluded from the CrUX dataset. |
Is sufficiently popular Exact numbers are not disclosed by Google, but the site (or page) must have a minimum number of visitors to be included in the CrUX dataset. |
| Does not use a sync passphrase The passphrase encrypts the synchronized data end-to-end, making it inaccessible to Google and excluding the data from the CrUX dataset. |
Your page must meet both the above criteria If your page is publicly discoverable but not sufficiently popular (or vice versa), it is excluded from the CrUX dataset. |
| Uses a supported platform Currently, the following platforms are supported: • Chrome Desktop on Windows, macOS, ChromeOS, and Linux operating systems. • Chrome Android, including mobile apps using Custom Tabs and WebAPKs. |
Origin and Page have same but separate eligibility criteria • If both Origin and Page meet eligibility criteria, both are included in the CrUX dataset. • If one of them doesn’t meet the eligibility criteria, the respective group may be excluded. • If both of them do not meet the eligibility criteria, both groups may be excluded (i.e., No data). |
| Platforms currently not supported: • Chrome on iOS • Android apps using WebView • Other Chromium browsers (e.g., Microsoft Edge) |
Data defaults to Origin in the absence of Page data If Page does not have sufficient data, only Origin data is provided (aggregate of all eligible pages). |
Essentially, your webpage (or website) will have CrUX data only if it meets Google’s origin/page criteria and if the user visiting your page meets their eligibility criteria for inclusion.
How is CrUX Data Measured?
Firstly, all the data collected is anonymized to ensure your visitors’ privacy.
CrUX data represents visitors’ real interactions with your website/page across diverse conditions.
These include:
- Multiple user environments
- Considers any device, location, network speed, etc. used to access your page.
- CrUX takes all of these into account and includes these differences in the dataset (provided the eligibility criteria are met).
- One value is provided for each metric that represents an average of all of these different environments.
- Full user sessions
- Metrics are captured for the full duration of your visitor’s session (i.e., beyond the initial page load).
- Certain metrics can vary based on how the visitor interacts with your page.
- As long as your visitor stays on your page or site, certain metrics can be updated based on the length of the user session.
- 28-Day rolling window
- Unlike lab (synthetic) data, CrUX data is not an instant shapshot of your page’s current performance.
- CrUX aggregates performance metrics over a 28-day period, providing an averaged view of real-world experiences.
- At any given moment, the data seen is an aggregate of the latest 28 day period.
- Only eligible data included
- Not all websites (or pages) or Chrome users automatically qualify for inclusion in the CrUX dataset.
- Page data will be included in the CrUX dataset only if it meets Google’s origin/page criteria.
- Pages must be publicly discoverable AND sufficiently popular.
- The user visiting your page must meet eligibility criteria for inclusion.
- User must have opted into usage statistics reporting, uses a supported platform, etc.
- Read more here
In addition to the above, the data undergoes sampling, filtering, and processing to ensure statistical accuracy while maintaining privacy.
Why Should Website Owners Care About CrUX?
Broadly speaking, paying attention to CrUX data can bring some practical benefits for website owners:
Real-World Feedback
CrUX gives you a direct glimpse into how your website performs for real users across the globe, offering a complementary perspective to lab (synthetic) results.
While lab tests are invaluable for controlled and repeatable analysis, CrUX highlights performance from the perspective of your actual audience, ensuring a well-rounded understanding of your visitors’ page experience.
Websites that load quickly and behave predictably help visitors accomplish their goals more effectively, whether that means making a purchase, finding information, or interacting with your page content.
Having access to this information can help you address such issues and equip you to provide a better browsing experience to all your visitors, regardless of their location or device.
Real-World Validation
CrUX data can validate and support your lab (synthetic) results.
If your CrUX data closely matches your lab (synthetic) tests, then that is proof that your optimization efforts are paying off.
On the other hand, if your lab (synthetic) results and CrUX data vary significantly, this could indicate things like:
- Performance differences for specific devices and/or slower network connections for your users
- E.g., older smartphones, 3G connection speeds, etc.
- E.g., older smartphones, 3G connection speeds, etc.
- Location differences between your core audience and GTmetrix testing location
- If your core audience is closer to your server but you tested with GTmetrix from a location far from the server, the scores may be lower than CrUX data reports
- If your core audience is closer to your server but you tested with GTmetrix from a location far from the server, the scores may be lower than CrUX data reports
- Poor experience beyond the specific page load
- Especially when comparing to Origin CrUX data
- Especially when comparing to Origin CrUX data
- More powerful hardware and faster connection speeds in the real world
- E.g,. Samsung Galaxy S24 Ultra on a Gigabit Fibre Wi-fi connection)
For website owners, understanding what these gaps represent can help you fine tune your website for a more consistent page experience for your visitors.
For visitors, this can translate into shorter wait times, more responsive pages, and stable visual layouts, all of which improve website engagement.
Your lab data will likely differ from your CrUX data
There is no guarantee that your lab results will 100% align with real user (CrUX) experiences, but having both results gives you a complete picture of how your website responds in different conditions.
SEO and Search Engine Rankings
It is well-known that Page Speed and Page Experience are important ranking factors for SEO.
As mentioned earlier, CrUX is not only the field data source for GTmetrix, but also PageSpeed Insights and the Core Web Vitals Report (in Google Search Console).
Even though Google does not explicitly say it, CrUX data is probably the dataset with the biggest impact on search rankings, given it reflects real user interactions.
For website owners, what this means is:
- Good CrUX data points to a good page experience (e.g., faster load times, better interactivity, etc.)
- Improvements in CrUX data may correlate with better visibility, higher traffic and conversions on your website
- Strong CrUX data may contribute to improved search engine rankings
Improved SEO means visitors are more likely to find your website in search results.
A good page experience should also translate to a superior browsing experience and increased engagement for your visitors, both of which can drive higher conversions and revenue for website owners.
The End Goal is the Same as With Lab (Synthetic) Data
Lab/synthetic data and CrUX data may have different sources and different methodologies, but they have a common goal – to help you optimize your website’s performance for your visitors.
Lab/synthetic and CrUX data are the dynamic duo of web performance. Together, they create a complete picture of your website’s performance.
Think of lab/synthetic data and CrUX data as the dynamic duo of web performance. Individually, they’re solid. But together, they create a complete picture of your website’s performance.
- Lab/synthetic data offers a reliable and consistent performance benchmark that is essential to help you test specific scenarios, pinpoint performance bottlenecks, and optimize for a wide variety of visitors.
- CrUX data on the other hand reflects what real users are actually experiencing in the wild, incorporating variables like device capabilities, internet speeds, and geographic factors.
The bottom line is any website owner who is serious about web performance needs both lab and CrUX data in their corner.
With CrUX now available in the GTmetrix Report, you can look at two complementary sets of data that can inform you (and confirm) if your web performance optimizations are bearing fruit in the real world.
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