There is always the alternative of doing feature detection instead. In addition, it is not practical to test every one of the less popular browsers and test for those Web features. This is the worst reason to use user agent detection because odds are eventually all the other browsers will catch up. Your site needs to use a specific Web feature that some browsers don't yet support, and you want to send those users to an older Web site with fewer features but that you know will work. Are you trying to check for the existence of a specific feature? Browser makers do pay attention to bug reports, and the analysis may hint about other workarounds for the bug. If the problem seems uncommon, it's worth checking if this bug has been reported to the browser vendor via their bug tracking system ( Mozilla WebKit Blink Opera). Also, experts, or people with another point of view, can give you ideas for working around the bug. Look, or ask, in specialized forums: you're unlikely to be the first to hit this problem. Are you trying to work around a specific bug in some version of a browser? Start by trying to identify why you want to do it. When considering using the user agent string to detect which browser is being used, your first step is to try to avoid it if possible. Feature-Policy: publickey-credentials-get.Reason: CORS preflight channel did not succeed.Reason: CORS header 'Origin' cannot be added.Reason: Credential is not supported if the CORS header 'Access-Control-Allow-Origin' is '*'.Reason: Multiple CORS header 'Access-Control-Allow-Origin' not allowed.

Reason: CORS header 'Access-Control-Allow-Origin' missing.

Reason: missing token 'xyz' in CORS header 'Access-Control-Allow-Headers' from CORS preflight channel.

Reason: expected 'true' in CORS header 'Access-Control-Allow-Credentials'.

Reason: Did not find method in CORS header 'Access-Control-Allow-Methods'.

Reason: invalid token 'xyz' in CORS header 'Access-Control-Allow-Methods'.

Reason: invalid token 'xyz' in CORS header 'Access-Control-Allow-Headers'.

Reason: CORS request external redirect not allowed.

Reason: CORS header 'Access-Control-Allow-Origin' does not match 'xyz'.

Safari browser version check