decoder.tools

User-Agent Parser

Break a User-Agent string down into browser, engine, OS and device.

Network, System & PacketsFree
INPUT
OUTPUT

The result appears here as you type.

Decoding runs in your browser. What you paste is not sent to a server.

A User-Agent parser interprets the User-Agent HTTP header — a string every browser sends identifying itself — extracting the actual browser, its version, the rendering engine and the operating system from a format thick with historical compatibility tokens.

Example

Input
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Safari/537.36
Output
Chrome 120.0 on macOS 10.15.7
Browser: Chrome 120.0
Operating system: macOS 10.15.7
Engine: WebKit/Blink
Form factor: Desktop

What is the User-Agent Parser?

User-Agent strings are an accident of history. Nearly every browser still begins with 'Mozilla/5.0' because early servers sniffed for it, and Chrome's string names Safari and KHTML for the same reason. The result is a header where almost every token is a compatibility claim rather than a fact, and parsing it means knowing which tokens to believe.

The reliable signals are the later ones: 'Chrome/120' before 'Safari' means Chrome; 'Version/17' before 'Safari' with no Chrome token means real Safari; 'Firefox/121' means Firefox; 'Edg/120' means Edge. Getting this wrong is how sites end up serving Safari-specific workarounds to Chrome.

The header is also being deliberately wound down. Chrome now freezes and reduces the detail it reports, moving to Client Hints (Sec-CH-UA headers) where sites request only what they need. Feature detection has always been the better approach; UA parsing remains useful for analytics, log analysis and bot identification.

How to use the User-Agent Parser

  1. Paste the User-Agent string from a log line or your browser's network tab.
  2. Read the identified browser, version, engine and operating system.
  3. Treat the result as a hint — the header is self-reported and freely faked.

When to use it

  • Analysing which browsers and versions appear in your access logs.
  • Identifying bot and crawler traffic by its declared agent.
  • Reproducing a bug reported by a user who pasted their UA string.

User-Agent Parser at a glance

HeaderUser-Agent, sent on every HTTP request
Mozilla/5.0A legacy compatibility token, not a real claim
SuccessorUser-Agent Client Hints (Sec-CH-UA)
Trustworthy?No — trivially spoofed by clients and bots

Frequently asked questions

Why does Chrome's User-Agent mention Safari and Mozilla?

Purely for backward compatibility with servers that once sniffed for those tokens. The string is a chain of historical claims; only the later, browser-specific tokens are meaningful.

Can a User-Agent be trusted?

No. It is a self-reported string any client can set to anything, which is why it should never gate security decisions — and why bots routinely present as ordinary browsers.

What replaces the User-Agent header?

User-Agent Client Hints: a set of Sec-CH-UA headers a site can request, giving structured, granular data with less passive fingerprinting surface than one long string sent to everyone.

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