This page is just a reference of all the known Steam APIs, I do not know how they work. Please do not email me with questions.
UNDOCUMENTEDGetLeagueData
https://api.steampowered.com/IDOTA2League_570/GetLeagueData/v1/
UNDOCUMENTEDGetLeagueInfoList
https://api.steampowered.com/IDOTA2League_570/GetLeagueInfoList/v1/
UNDOCUMENTEDGetLeagueNodeResults
https://api.steampowered.com/IDOTA2League_570/GetLeagueNodeResults/v1/
UNDOCUMENTEDGetLeaguesData
https://api.steampowered.com/IDOTA2League_570/GetLeaguesData/v1/
UNDOCUMENTEDGetLiveGames
https://api.steampowered.com/IDOTA2League_570/GetLiveGames/v1/
UNDOCUMENTEDGetMessages
https://api.steampowered.com/IDOTA2League_570/GetMessages/v1/
UNDOCUMENTEDGetPredictionResults
https://api.steampowered.com/IDOTA2League_570/GetPredictionResults/v1/
UNDOCUMENTEDGetPredictions
https://api.steampowered.com/IDOTA2League_570/GetPredictions/v1/
UNDOCUMENTEDGetPrizePool
https://api.steampowered.com/IDOTA2League_570/GetPrizePool/v1/