How User-Agent works
Browser user agents are long, historical strings that all start with Mozilla/5.0, and Chrome now freezes most of the detail (OS version, device model) in favour of User-Agent Client Hints (Sec-CH-UA headers). Prefer feature detection over parsing it. Bots and scripts should send an honest name with contact details.
Examples
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36User-Agent: inventory-sync/2.1 (+https://example.com/bot; ops@example.com)Check it
# Show the request headers curl sends (lines starting with >)
curl -sv -o /dev/null https://example.com 2>&1 | grep '^>'Paste a full set of response headers into the HTTP header checker to get every header explained and common mistakes flagged.
Related headers
- Accept: lists the response formats the client prefers, with optional weights.
- Sec-Fetch-Site: tells the server whether a request came from the same origin, the same site, another site, or the user directly.
- Host: names the domain (and port) the request is for, so one server can host many sites.
More requests, redirects and more headers
Location , Retry-After , Link , Clear-Site-Data , Server-Timing .
Sources
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Frequently asked questions
What does the User-Agent header do?
The User-Agent request header identifies the client software: browser and version, operating system, or a bot or library name. Browser user agents are long, historical strings that all start with Mozilla/5.0, and Chrome now freezes most of the detail (OS version, device model) in favour of User-Agent Client Hints (Sec-CH-UA headers). Prefer feature detection over parsing it. Bots and scripts should send an honest name with contact details.
How do I see the User-Agent header?
Open your browser’s dev tools, select a request in the Network tab and look under Request Headers. On the command line, "curl -v https://example.com" prints the request headers it sends, marked with ">".