API can be found Here. To get an API key you can request one under the support tab on here.
API Examples/How to get started: here
The API is documented using Swagger which means you can use the documentation file to automatically generate API clients for essentially every language. The Swagger Editor offers this functionality without needing to run any local tooling.
/user/{userid} using this you can get the moderation state, id, and username of the specified user, this can be used to check if they are whitelisted or not./rank This will get you a paged list of the top ranked players. This request requires a Style Id and a Game ID, a page is optional./rank/{userid} This will get you info about a player most notably their rank, skill, and placement. This request requires a Style Id, User ID, and Game ID/time/{timeid} This will give you info about a certain time. To get a Time Id you can request a users times and get the Time Ids from that. Requires a Time Id/time/{timeid}/rank This will get the rank of the time, not very useful or used very often. Requires Time Id/time/recent This gets the 50 most recent times. No required paramaters /time/recent/wr This will give you the 10 most recent World Records. Requires Style Id, and Game Id/time/map/{mapid} Gets all the times on a map sorted by ascending order. Requires Map Id. Optional Style Id, Page/time/map/{mapid}/wr Gets the World Record of the map. Requires Map Id and Style Id/time/user/{userid} Gets all times from a user. Requires User Id. Optional Map Id, Style Id, Game Id, Page/time/user/{userid}/wr Gets all World Records from a user. Requires User Id, Style Id, and Game Id./map Gets a list of maps and extra info about them, most notably Creator, map id, and playcount. Optional Game Id, Page(200 Per page)/map/{mapid} Gets info about a certain map. Required Map Id