The structure of URLs for the API is: https://api.whatismybrowser.com/api/v3/end-point
Version 3 has a more streamlined approach to its API End points: there are only two, the Detect API End Point, and the Version Numbers API End Point.
The request structure varies by endpoint but the general idea is that if you're POST-ing something for us to process (eg. all your visitor's HTTP Headers for us to Detect their system), you'll send the POST body as valid JSON and we'll take it from there.
To get the latest version numbers, it will be a GET request.
Check the documentation for the end point in question.
Note that we also allow and fulfil OPTIONS requests - without affecting your API quota - so that Javascript based API requests work (many JS implementations send a pre-flight OPTIONS request which fails if we don't allow OPTIONS).
Each API request needs to be Authenticated, read the section on Authentication for more information.
Continue reading: Common Response elements.