An user agent is a string of information your browser sends when executing a HTTP request with a website. The user agent contains your operating system and browser make and version. The user string will also contain computer architecture, such as 64-bit or Intel Mac.

The user agent enables the website to better understand what type of device and browser is visiting and how best to render the webpage. You can read about user agents in our article Understanding User Agents and What Websites can See.

User agents are what the browser sends to the website but that does not mean they are correct. For example, a computer running MacOS 14 and a M1 chipset identifies itself as an Intel Mac running OS X. What the user string is doing in this example is telling the website to render pages like it is a Intel Macintosh running OS X.

User agent strings always start with Mozilla/5.0 for historical reasons. It's a good read to understand why. User agents contain operating system, rendering engines, and browser versions.

The short answer is you can't lookup someones user agent. The reason why you can't lookup an user agent is because a device will have different user agents for each browser that could be used. An user agent is not device specific and is only visible during the HTTP request. Browsers such as Edge, Chrome, Safari, and FireFox will have different user agents and will also be different based on the operating system in which they run.

If you are a website owner then you can log a person's user agent when they load a specific page. For example, this website displays the visitors User Agent on page load of this page but does not log it.

Yes, you can change your user agent. The first way is by changing browsers as each browser and operating system combination will have its own user agent. You can also spoof your user agent using software. This technique will allow you to use a different user agent string than what your browser would normally use.

Spoofing your user agent is often used by web developers to test their web apps and the practice is not illegal in the United States. We would recommend checking with your local jurisdiction before spoofing your user agent.

Spoofing your user agent is not something we recommend and ultimately keep your browser and operating system updated is the best method to protecting yourself. In some cases, the user agents of bots are spoofed to look like something they are not.

User agents serve the purpose of improving user experience but they are not exempt from privacy concerns. A website can learn what browser and operating system an visitor is using and combined with their IP begin to form a fingerprint on the visitor. In some cases malicious websites can take advantage of vulnerabilities by using the visitors user agent to see browser and operating system version.

We recommend keeping your operating system and browser updated to protect from being exploiting by known vulnerabilities. Using software to spoof your user agent can also reduce the risk but may also impact your user experience. In general, there is little risk in a vast majority of websites knowing your user agent.