What is a User-Agent string?

The User-Agent (UA) is a header your browser sends with every HTTP request. It declares the browser, rendering engine, operating system, and sometimes device family. Servers use it to deliver compatible content and gather analytics.

Can a User-Agent be spoofed?

Yes — trivially. Any client (browser extension, curl, bot, scraper) can send any UA it wants. Treat UA as a strong hint, never as proof of identity or authenticity.

Why do all major browsers still say 'Mozilla/5.0'?

Historical compatibility. Early servers gated features behind 'Mozilla'-prefixed UAs; every modern browser keeps the prefix to avoid breaking sites that still rely on the old check.

How do I detect bots and crawlers?

Look for well-known substrings — googlebot, bingbot, duckduckbot, slurp, spider, crawler — and verify against the bot's published IP ranges. UA alone is not a security control.

What is User-Agent Client Hints?

A modern replacement for the UA string. Chrome (and others) are freezing UA values and shifting detailed device/version data to opt-in Client Hints headers like Sec-CH-UA, Sec-CH-UA-Platform, and Sec-CH-UA-Mobile.

Privacy

User Agent Checker

Parse any User-Agent string into browser, engine, OS, and device. Defaults to your own.

Detecting…

What this tool does

Paste any User-Agent string and the parser breaks it into browser family, version, rendering engine, operating system, device class, and a bot-likelihood signal. Defaults to your own browser's UA.

Why it matters

UA strings drive analytics segmentation, conditional content delivery, bot detection, and compatibility shims. Reading them correctly — and understanding their limits — is a core skill for anyone running a website, debugging a crawl, or investigating suspicious traffic.

How to interpret results

Browser + version — derived from the canonical token (Chrome/, Firefox/, Safari Version/).
Engine — Gecko (Firefox), WebKit/Blink (Safari/Chromium), Trident (legacy IE).
OS — Windows NT mapping, macOS X build, Android version, iOS version, ChromeOS, Linux.
Device class — heuristic from Mobi / iPhone / iPad / Tablet tokens.
Bot / crawler — pattern match for common crawler tokens; not exhaustive.

Common use cases

Debug a user-reported issue by parsing the UA from their bug report.
Filter access logs to separate humans from bots.
Confirm a server is sending the UA you expect (curl, fetch, Node, scraping libraries).
Test how UA freezing (Chrome's UA Reduction) changes detected versions.

Limitations

UA parsing is heuristic. Any client can lie — including malicious bots impersonating Googlebot. For authoritative bot identification, cross-check against the bot's published IP ranges (Google, Bing, and others publish these). For modern Chrome, also read Sec-CH-UA-* Client Hints headers; the legacy UA string is being frozen.

Methodology

Parsing uses regex tokenisation against the documented UA grammar for each major engine. No external lookup is performed — the parser is entirely deterministic and runs client-side. See methodology for the platform's transparency model.

Related tools & guides

Frequently asked

What is a User-Agent string?: The User-Agent (UA) is a header your browser sends with every HTTP request. It declares the browser, rendering engine, operating system, and sometimes device family. Servers use it to deliver compatible content and gather analytics.
Can a User-Agent be spoofed?: Yes — trivially. Any client (browser extension, curl, bot, scraper) can send any UA it wants. Treat UA as a strong hint, never as proof of identity or authenticity.
Why do all major browsers still say 'Mozilla/5.0'?: Historical compatibility. Early servers gated features behind 'Mozilla'-prefixed UAs; every modern browser keeps the prefix to avoid breaking sites that still rely on the old check.
How do I detect bots and crawlers?: Look for well-known substrings — googlebot, bingbot, duckduckbot, slurp, spider, crawler — and verify against the bot's published IP ranges. UA alone is not a security control.
What is User-Agent Client Hints?: A modern replacement for the UA string. Chrome (and others) are freezing UA values and shifting detailed device/version data to opt-in Client Hints headers like Sec-CH-UA, Sec-CH-UA-Platform, and Sec-CH-UA-Mobile.