What is a User Agent (UA) string?

A User Agent is a text header sent by web browsers and apps to web servers with every HTTP request. It tells the server which browser, operating system, rendering engine, and device is requesting the page so servers can tailor HTML, CSS, or security protocols.

Why do all modern user agents start with "Mozilla/5.0"?

This is a historical quirk in web history. Early websites were built specifically for Netscape Navigator (code-named Mozilla). Later browsers (like Internet Explorer and Chrome) prefixed their strings with Mozilla/5.0 so old web servers would serve them modern pages rather than bare-bones fallbacks.

Can User Agent strings be spoofed?

Yes. Anyone can change their User Agent string using browser developer tools, browser extensions, or HTTP clients like cURL. While useful for analytics and troubleshooting, UA strings should not be relied upon solely for critical security authentication.

Can this tool detect web crawlers and bots?

Yes. The parser recognizes common search engine crawlers and web scrapers including Googlebot, Bingbot, Baiduspider, YandexBot, and DuckDuckBot.

Is my User Agent logged or saved to a database?

No. The parsing is executed 100% locally in your web browser with client-side JavaScript. No data is stored or tracked.

User Agent Parser & Detector

Parse and inspect User Agent strings to detect Browser, Version, OS, Device Type, and Rendering Engine.

100% free
Private in browser
No signup
No watermarks

HTTP User-Agent String

Browser

Unknown Browser

vUnknown

Operating System

Unknown OS

Detected

Device Type

Desktop

👤 Human User

Engine

Unknown Engine

Rendering Pipeline

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About User Agent Parser & Detector

The User Agent Parser analyzes HTTP User-Agent strings to break down complex client headers into structured information: Browser brand (Chrome, Safari, Firefox, Edge), major & minor versions, Operating System (macOS, Windows, iOS, Android, Linux), rendering engine (Blink, WebKit, Gecko), and hardware category (Desktop, Mobile, Tablet, Bot).

How to use User Agent Parser & Detector

View your live browser User Agent automatically or paste any custom User-Agent string.
Review the parsed breakdown of Browser, OS, Engine, and Device Type.
Inspect device category flags and bot detection indicators.
Copy the structured JSON breakdown or summary text for logging and analytics.

Key features

Auto-detects live browser User Agent (`navigator.userAgent`) on page load
Comprehensive pattern matching for Chrome, Safari, Firefox, Edge, Opera, Samsung, and iOS
Detailed OS identification including macOS, Windows, Linux, Android, and iOS
Search engine crawler and bot identification (Googlebot, Bingbot, Yandex)

Frequently asked questions

What is a User Agent (UA) string?: A User Agent is a text header sent by web browsers and apps to web servers with every HTTP request. It tells the server which browser, operating system, rendering engine, and device is requesting the page so servers can tailor HTML, CSS, or security protocols.
Why do all modern user agents start with "Mozilla/5.0"?: This is a historical quirk in web history. Early websites were built specifically for Netscape Navigator (code-named Mozilla). Later browsers (like Internet Explorer and Chrome) prefixed their strings with Mozilla/5.0 so old web servers would serve them modern pages rather than bare-bones fallbacks.
Can User Agent strings be spoofed?: Yes. Anyone can change their User Agent string using browser developer tools, browser extensions, or HTTP clients like cURL. While useful for analytics and troubleshooting, UA strings should not be relied upon solely for critical security authentication.
Can this tool detect web crawlers and bots?: Yes. The parser recognizes common search engine crawlers and web scrapers including Googlebot, Bingbot, Baiduspider, YandexBot, and DuckDuckBot.
Is my User Agent logged or saved to a database?: No. The parsing is executed 100% locally in your web browser with client-side JavaScript. No data is stored or tracked.