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.
UNDOCUMENTEDPOSTGetGamesWithNotes
https://api.steampowered.com/IUserGameNotesService/GetGamesWithNotes/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
UNDOCUMENTEDPOSTGetNotesForGame
https://api.steampowered.com/IUserGameNotesService/GetNotesForGame/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
string No
uint32 No
bool NoInclude the text content. If not passed, content will be empty in the response objects but title will be available.