A Curiosity??

[jPaulB]

Hi Everybody,

It's just occured to me.
When I visit a web site, it seems that the server will 'somehow' know what kind of device I am using and then format the display accordingly.
How does that server know what kind of device I am using? (I guess my device tells them).
What else will a server know about a visior. Are any serial numbers exchanged? Where can I go to know more about this?

 

[John Joe]

Websites detect your device type mainly through the User-Agent string your browser sends, along with other signals like client hints and feature detection.

 

[VBService]

Servers detect your device type primarily through information your browser sends automatically in HTTP requests. They also gather other details like your IP address and can infer more if you interact with the site.

Your browser includes a "User-Agent" string in every request to a server, revealing details such as the browser name (e.g., Chrome), version, operating system (e.g., Windows, iOS), and sometimes device model or screen resolution.
This allows servers to serve mobile-optimized pages or adjust layouts without needing separate sites.
JavaScript on the page can further probe features like screen size or touch support, sending that data back.

Servers log your IP address (revealing approximate location and ISP), request timestamp, visited pages, referrer (previous site), and language preferences from headers.
If you log in, cookies, or use third-party trackers (e.g., Google Analytics), they access emails, profiles, or browsing patterns.
No hardware serial numbers (like MAC addresses or device IDs) are exchanged by default-those stay local unless you explicitly share them via apps.

• User-Agent header
• How do webservers reliably determine the device that is sending requests?
• Understanding how server-side tracking works
• What information does a server know about the client that does the request?