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What does the user agent tell you?
We’ve written about changing your browser’s user agent before – but what exactly is a user agent, anyway? A user agent is a “string” – that is, a line of text – identifying the browser and operating system to the web server.
Why do all user agent strings start with Mozilla?
It spoofs Netscape by starting its User-Agent with Mozilla/ because web servers were routinely browser sniffing and serving pages with frames – a feature supported by both Netscape and IE, but not other browsers of the era – to Netscape only.
Is the user-agent unique?
User-Agents also provides one of the data points for fingerprinting users without the use of cookies. It’s included with every HTTP request and can potentially be very long and unique to a user in certain uncommon situations.
Is user-agent required?
Whether or not it’s REST, it’s still HTTP, and subject to the HTTP specification. Per RFC 7231: A user agent SHOULD send a User-Agent field in each request unless specifically configured not to do so. Just to clarify, the client code should set a User Agent.
Why do web servers use the user agent string?
Web servers don’t really care what the exact user agent string is – they just check to see if it contains a specific word. Web servers use user agents for a variety of purposes, including: Serving different web pages to different web browsers.
What does it mean to be a user agent in a browser?
The contents of the user agent field vary from browser to browser. Each browser has its own, distinctive user agent. Essentially, a user agent is a way for a browser to say “Hi, I’m Mozilla Firefox on Windows” or “Hi, I’m Safari on an iPhone” to a web server.
How is browser detection using the user agent string?
In those rare cases where behavior differs between browsers, instead of checking the user agent string, you should instead implement a test to detect how the browser implements the API and determine how to use it from that. An example of feature detection is as follows.
Is the user agent string similar to Firefox?
The Chrome (or Chromium/blink-based engines) user agent string is similar to the Firefox format. For compatibility, it adds strings like “KHTML, like Gecko” and “Safari”.