Browser User-Agent strings are a strange artifact of web history — most modern browsers still identify themselves partly as "Mozilla" for backward-compatibility reasons that stopped mattering decades ago. Reading one accurately means knowing which substrings are actual signals and which are just legacy noise.
Order of checks matters more than you'd think
Chrome, Edge, Opera and several other browsers are all built on the same underlying engine and include "Chrome/" in their own User-Agent string, so a naive check for "Chrome" alone will misclassify Edge and Opera users as Chrome users. Getting this right means checking for the more specific browser markers first, and only falling back to the generic engine string last.
It's a client-supplied string, not a guarantee
Because the browser itself sends this value, anyone can override it — browser extensions, developer tools device emulation, and deliberate spoofing all change what a server sees. Useful for a quick guess about someone's likely browser and OS; not a reliable basis for a security decision.
TeckForge's User-Agent String Parser breaks a pasted User-Agent string down into a best-guess browser, rendering engine, operating system and device type, or can just read and explain your current browser's own string with one click.
