What LUX does *not* collect
If you have GDPR concerns, you will find it helpful to know that LUX does not gather any personally identifiable information (PII) such as IP addresses, names, emails, or other metrics that could identify a user. You can see all the LUX metrics we collect here. LUX also doesn't do any ongoing user tracking. It tracks individual session, but if a user returns to the site later, that is a new, unique session.
What LUX does collect
You can see an example of the LUX data gathered by clicking on a row in the LUX Live dashboard in your account.
The LUX information gathered is broken into the following categories. For more details about each metric, see this support article.
This category includes meta information about the page.
Page label (defined by LUX.pagelabel;
document.titleused as a fallback)
This category includes information about the browser that loaded the page.
Location - city, country, continent
Browser user-agent string
Normalised browser information based on user-agent
Device type (mobile, tablet, desktop) based on user-agent
Device memory - estimated based on
This category includes information from the Navigation Timing specification.
This category includes information from the Paint Timing specification, and other paint- or render-related metrics.
first-paint - aka, Start Render
Largest Contentful Paint (LCP)
Cumulative Layout Shift (CLS)
The Long Tasks API is used to gather information about the CPU including:
Total CPU time
Number of Long Tasks
Longest Long Task
Median Long Task
First CPU Idle
Marks and measures captured using the User Timing specification are reported in this category. We believe that User Timing marks and measures (aka, "Custom Metrics") are the best performance metrics to use because they are specific to what is most important in your site. Read the User Timing and Custom Metrics blog post for more information.
SpeedCurve is focused on creating fast, joyous user experiences. We feel this requires combining typical performance timing metrics with information about website design. This category includes several innovative metrics that are unique to SpeedCurve.
External Scripts - The total number of scripts fetched by the page.
Stylesheets - The total number of stylesheets fetched by the page.
Blocking Scripts/Stylesheets - The total number of scripts and stylesheets that are fetched in synchronous mode and thus block the HTML parser and rendering.
Average DOM Depth - The average depth of a DOM element in the page's DOM hierarchy. This affects CSS and rendering performance.
# DOM Elements - The total # of DOM elements. This affects CSS and rendering performance.
HTML Size - The transfer size of the HTML document.
Inline JS Size - The uncompressed size of any inline <script> tags.
Inline CSS Size - The uncompressed size of any inline <style> tags.
Connection Type - The effective connection type of the user's network.
Viewport - The width and height of the browser viewport. This is important for knowing how much content is visible to the user when the page loads.
Document - The width and height of the document. This is important for determining how much of the content is not visible and could potentially be lazy-loaded to improve initial rendering.
Interaction (IX) Metrics
For many websites, how quickly users engage with the page is an important user experience metric. If these metrics increase it could be a sign that the page is rendering slower, or a design change has made the site more difficult for users. This category captures metrics about how and how quickly users engage with the page.
First IX Type - The first type of interaction the user had with the page: scroll, click, or keypress.
First IX Time - When the first interaction time occurred (relative to navigationStart).
Element ID clicked - The ID or data-sctrack attribute of the DOM element that was clicked or keypressed. See the LUX data-sctrack API for more information.
Interaction co-ordinates - the X and Y co-ordinates of the input event (if available).
First Input Delay (FID).
You can use the LUX API to gather any data you want, for example, cart size, A/B testing, and conversion information. For more information see the LUX Customer Data support article.
We're constantly extending LUX to gather other valuable information beyond what is listed here. For more details about each metric, see this support article.