A user agent is any client that makes requests to a server on a user's behalf, such as a browser, crawler or app. It identifies itself using the User-Agent request header.
Why it matters
Servers use the header for analytics, serving mobile or desktop layouts, and recognizing search engine bots. It is easy to fake, so it must not be trusted for security. Monitoring tools send their own user agent, which lets you identify or allow them in your logs and firewall.
Client hints are a newer, more privacy-friendly mechanism that is slowly replacing detailed user agent strings in some browsers.
Example
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0 Safari/537.36Nearly all browsers begin with Mozilla/5.0 for historical compatibility reasons.
Common mistakes
- Blocking by user agent alone and missing bots that fake it.
- Serving different content to bots and users based only on this header.
- Relying on it for device detection when responsive CSS would do.
Related
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यह पेज सामान्य जानकारी है, जिसे हमारी संपादकीय टीम ने लिखा है और दस्तावेज़ीकरण बदलने पर अपडेट किया जाता है। सर्वर और प्रदाता अलग-अलग होते हैं, इसलिए बदलाव पहले सुरक्षित तरीके से जाँचें। देखें: संपादकीय नीति और अस्वीकरण.