Flicker Effect
Also known as Flash of Original Content (FOOC), this is a negative user experience that often occurs with Client-Side A/B Testing. Users see a brief "flicker" of the original page content before JavaScript runs to replace it with the test variation. This visual disruption can be jarring, erode user trust, and signal that the page is not well-optimized.
Related web performance terms
- Fail-safe Mechanism
A fail-safe mechanism is a core architectural principle of Speed Kit that guarantees the service will never slow down a website.
- Fetch Priority (`fetchpriority="high"`)
The fetchpriority="high" attribute is an HTML attribute that tells the browser to prioritize loading a specific resource (like an image or script) higher than other resources of the same type.
- Field Data (Real User Monitoring - RUM)
Field data is performance data collected from the real users visiting your website in their actual environments. It captures the true user experience across the full spectrum of devices, network co…
- First Contentful Paint (FCP)
First Contentful Paint (FCP) is a performance metric that measures the time from when a user initiates loading the page until the first piece of content (text, image, or other element) is rendered on the screen.