Reading a User-Agent header

Tweet by @jschauma:

Whenever a browser makes an HTTP request to a server, the browser sends in a User-Agent header, so the server can know what kind of a browser/agent the request is coming from. I’m writing this post in a Safari browser in macOS and the string it sends is:

User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/604.1.38 (KHTML, like Gecko) Version/11.0 Safari/604.1.38

It says Mozilla at the beginning, but it’s not Firefox.

Confusingly, the User-Agent string of Google Chrome has both Mozilla and Safari in addition to Chrome:

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36

These strings will change depending on both the browser version and the OS you are on.

While these strings seem cryptic, you can use this handy guide from MDN to identify the browser from User-Agent strings: https://developer.mozilla.org/en-US/docs/Web/HTTP/Browser_detection_using_the_user_agent#Browser_Name

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