Why this is sometimes needed
Support teams and bug reports often need to know exactly which browser, version and operating system someone is using to reproduce an issue - "it doesn't work" is much easier to debug as "Chrome 118 on Windows 11". Everything here comes straight from your browser's own JavaScript APIs, detected the moment the page loads, with nothing sent to a server.
Why browser detection relies on checking markers in order
Many Chromium-based browsers (Edge, Opera) include "Chrome" somewhere in their user agent string for website compatibility, even though they aren't actually Chrome - so detection has to check for each browser's more specific, unique marker first (like "Edg/" for Edge) before falling back to the generic Chrome check, or every Edge or Opera user would get misidentified as using Chrome.
Why screen resolution and viewport size are shown separately
Screen resolution is your monitor's full physical pixel dimensions, while viewport size is how much of that space your actual browser window (minus toolbars, sidebars, and other chrome) is currently showing - two numbers that are often different and both independently useful when debugging a layout issue reported by someone else.
Why this is useful beyond just curiosity
Pasting this page's output directly into a bug report or support ticket gives the person fixing the issue exact technical details instantly, rather than relying on a description like "it's on my phone" that leaves out the specific browser, version, and screen dimensions that often explain why an issue happens on one setup and not another.