Sec-CH-UA
- Input
- Sec-CH-UA: "Not A(Brand";v="99", "Google Chrome";v="121", "Chromium";v="121"
- Expected output
- Chrome 121, Chromium 121
Sent automatically (low-entropy hint) without needing Accept-CH.
user agent client hints browser
User-Agent Client Hints — the future of browser detection
User-Agent Client Hints is the modern evolution of the UA string, designed to reduce passive fingerprinting without removing servers' ability to adapt content. Understanding this transition is essential for developers who depend on browser detection.
How UA-CH works
- The server sends the Accept-CH header listing the desired hints (e.g. Sec-CH-UA-Platform, Sec-CH-UA-Mobile). The browser then includes only those fields in subsequent requests. UA-CH is opt-in, reducing the passive fingerprinting surface.
Available hints
Safe use
- Input
- context + tool result
- Expected output
- interpreted with limits and next steps
Use the result as technical or educational support, keeping the tool limits explicit in the workflow.
Full tool FAQ
It is an HTTP header sent by the browser with every request, in the format: "BrowserName/Version (OS; Architecture) Compatibility/1.0 Engine/Version". The syntax is defined by RFC 7231 and was originally created so servers could adapt responses for different clients.
Frequently asked questions
Are UA Client Hints available in all browsers?
UA-CH was introduced in Chrome 89 and is available in all Chromium-based browsers (Edge, Opera, etc.). Firefox and Safari have resisted adoption for privacy reasons — they prefer reducing the UA rather than replacing it with a hints system. Check MDN for current status.
Does this page replace official or professional review?
No. It helps explain the scenario and use the tool more safely, but real decisions should consider official sources, full context and qualified guidance when needed.