Responsive Viewer might be a bit more popular than Facebook Design Resources. We know about 2 links to it since March 2021 and only 2 links to Facebook Design Resources. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
Spotify isn't doing anything unique here, and it's not really a marketing campaign to explain away their UI. It's more of a showcase for hiring professionals, developers/designers/etc. Facebook has a similar one -> https://design.facebook.com/. Source: almost 3 years ago
Also, read anything published by Design @ Facebook. Source: about 3 years ago
Bonus! Useful Chrome extension for Responsiveness Testing. - Source: dev.to / 12 months ago
This chrome extension with all of the breakpoints set up https://chrome.google.com/webstore/detail/responsive-viewer/inmopeiepgfljkpkidclfgbgbmfcennb. Source: over 1 year ago
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