HTTP headers
User-Agent HTTP Header Meaning
User-Agent identifies the client software making the request.
Meaning
The client is sending a product string that may describe browser, engine, device, or bot identity.
Where it appears
Browsers, crawlers, CLI tools, and API clients send it on requests.
What to check
Treat it as client-provided text; use feature detection or explicit APIs instead of trusting it for security.
Example
User-Agent: Mozilla/5.0 ...References
- Registry
- IANA HTTP Field Name Registry
- Guide
- MDN User-Agent