User-Agent
The User-Agent header is an HTTP request field, defined in RFC 9110 section 10.1.5, that lets a client identify the software making the request -- conventionally a string of product names and versions, such as a browser name, its rendering engine, and the operating system it runs on. Servers and clients both use it informally: RFC 9110 notes that servers often scan the User-Agent value, and clients often scan a server's own Server field, to work around known bugs or poorly chosen defaults in a specific version, rather than as part of any formal negotiation. Because the field is client-supplied, with no fixed schema beyond a list of product tokens and comments, it can be spoofed, omitted, or trimmed, which is why some browsers now send a shorter, less detailed User-Agent string by default for privacy.
By AdminKit team, Netbase JSC · Updated