User Agent Parser

The User-Agent header is the messy, free-form string browsers send to identify themselves. This parser uses pragmatic regex matching (the same approach as ua-parser-js) to extract the browser name + version, rendering engine, OS + version, device type/vendor/model, and CPU architecture. Auto-fills with your current browser's UA on load. Useful for analytics debugging, bot identification, and understanding what your server logs are seeing.

The string is a fossil record of thirty years of compatibility lies, which is why every parser is regex guesswork rather than a specification. Chrome still announces itself as Mozilla/5.0 and claims to be like Gecko and Safari, none of which is true, because sites once sniffed for those tokens before serving the good version of a page. Every browser inherited the habit, so the header is a list of what a browser wants to be mistaken for, in historical order.

Useful detail is being deliberately removed. Chrome cut the version number in the UA down to its major release and froze the platform string years ago and moved the real values behind Client Hints, Safari has reported a fixed macOS version since Catalina, and both iPadOS and desktop-mode browsers identify as something they are not. A parser reading those strings reports what the browser wants reported, which for OS version in particular is now a constant rather than a fact.

Nothing here is a security boundary, which is the important part. The header is a request field the client fills in, so a bot that wants to look like Chrome simply says so, and feature detection is the only reliable way to know whether something is supported. Blocking on user agent filters out honest crawlers and inconveniences real users on unusual browsers while stopping nobody who cares.

The device model field is the least trustworthy of the lot. Android vendors fill it with anything from a marketing name to an internal codename, iOS never reveals it at all, and desktop browsers leave it empty. An analytics breakdown by device model is a breakdown of what Android manufacturers chose to disclose.