User-Agent String Parser

How this reads your output

The string is matched against patterns in a deliberate order, because user-agent strings are an accumulated fiction. Every browser claims to be Mozilla, most claim to be Safari, and Chromium-based browsers all claim to be Chrome, each layer added to get past sniffing that excluded it. Edge is therefore checked before Chrome, Chrome before Safari, and so on. Automated clients are detected separately, since they usually identify themselves plainly.

What the results mean

Rendering engine

Blink, WebKit or Gecko. More useful than the browser name for anything to do with rendering behaviour, since every Chromium browser shares one engine.

Frozen values

Windows reports 10.0 regardless of the real version and macOS reports 10.15.7 permanently. Both are deliberate, to reduce fingerprinting.

Automated client

The string identifies itself as a crawler or a library. Well-behaved automation says so; anything hostile does not.

Common problems and fixes

Analytics reports an impossible browser or version

Either a client with a modified user-agent, which privacy tools do routinely, or a bot copying a real browser string. Neither is detectable from the string alone. Behaviour is a far better signal than declaration: request rate, whether assets are fetched, and whether script runs at all.

Feature detection based on the user-agent broke a browser

It always does eventually, which is why the whole convention exists. Test for the feature instead: check whether the function or property is present rather than deciding from a version number. Where you genuinely need platform information, Client Hints are the supported route and give the browser control over what it reveals.

Frequently asked questions

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