| Term |
Metadata |
Definition |
Relevant Links
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One or two sentences |
- Full definition
- Related tests/coverage
- Results
- User research
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| SpeedIndex |
Visual |
(SI) is a page load performance metric that shows you how quickly the contents of a page are visibly populated. It is the average time at which visible parts of the page are displayed. Expressed in milliseconds, and dependent on the size of the viewport, the lower the score, the better. |
MDN Documentation
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| Contentful SpeedIndex |
Visual |
This metric uses edge detection to calculate the amount of “content” that is visible on each frame. It was designed to have a good metric to measure the amount of text that is visible and ignore the impact of popup or login screens at the end of a page load. |
sitespeed.io documentation
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| Perceptual SpeedIndex |
Visual |
A metric that measures the above-the-fold visual performance of a webpage, while accounting for the layout stability. |
* Perceptual Speed Index (PSI) for measuring above-fold visual performance of webpages
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| Visual Completeness |
Visual |
The point in time when a web browser has finished rendering viewable content in the viewport, but not the entire page. |
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| First Paint event |
Standard |
The time between navigation and when the browser renders the first pixels to the screen, rendering anything that is visually different from what was on the screen prior to navigation. |
MDN documentation
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| First Contentful Paint |
Standard |
How long it takes the browser to render the first bit of content from the DOM providing the first feedback to the user the page is actually loading. |
https://developer.mozilla.org/en-US/docs/Glossary/First_contentful_paint
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| DOMContentLoaded event |
Standard |
A DOM event that is fired once the underlying document has finished being parsed and loaded, but before any of its additional resources (stylesheets, images, subframes) have finished loading. |
MDN documentation
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| Onload event |
Standard |
A DOM event that is fired once the underlying document has finished loading, including all of its stylesheets, images and subframes. This does not include additional resources that start to load due to script. |
MDN Documentation
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| Time to Interactive |
Proposed standard |
(TTI) is a non-standardized web performance 'progress' metric defined as the point in time when the last Long Task finished and was followed by 5 seconds of network and main thread inactivity.
- The page has displayed useful content
- Event handlers are registered for most visible page elements
- When a user interacts with the page, the page consistently responds within 50ms - the user does not experience jank.
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| Cold page load |
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browser started and stabilized/idle, same profile dir as previous, site not loaded or cache cleared |
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| Warm page load |
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browser started and stabilized/idle, same profile dir as previous, site already loaded once, any click-throughs clicked |
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| Reload |
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To re-request the rendering of a document. This may mean re-retrieving the entire document and any of its resources off of the network, or might mean reloading the resources out of a local cache. |
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| Backwards/Forwards navigation |
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| Level 1 cookie blocking |
Tracking Protection |
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| Level 2 cookie blocking |
Tracking Protection |
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| Level 1 content blocking |
Tracking Protection |
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| Level 2 content blocking |
Tracking Protection |
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