Request negotiation · Request header

User-Agent

The client software identifying itself.

What is User-Agent?

The User-Agent string names the browser, engine, OS, and often the device. It is famously convoluted for historical reasons.

Set automatically by browsers and HTTP libraries. Read for analytics and rare compatibility branching.

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

User-Agent can be trivially spoofed and is being reduced by modern browsers. Do not use it as a security control.

Which media types the client can process.

Accept-Encoding

Which content encodings (compressions) the client accepts.

Accept-Language

Preferred human languages for the response.

Host

The requested host name and port.

Referer

The URL of the previous page that led to this request.