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.
PUBLISHERGETCheckAppOwnershipv4
https://partner.steam-api.com/ISteamUser/CheckAppOwnership/v4/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user
uint32 Yes AppID to check for ownership
PUBLISHERGETGetAppPriceInfo
https://partner.steam-api.com/ISteamUser/GetAppPriceInfo/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user
string Yes Comma-delimited list of appids (max: 100)
UNDOCUMENTEDGETGetDeletedSteamIDs
https://api.steampowered.com/ISteamUser/GetDeletedSteamIDs/v1/
NameValueTypeRequiredDescription
click to setstring Yes Steamworks Web API publisher authentication key.
uint64 Yes An unsigned 64-bit value used to page through deleted accounts. Pass 0 when calling this API for the first time, then pass the value returned from the previous call for each additional request. This value will need to be stored on your server for future calls.
GETGetFriendList
https://api.steampowered.com/ISteamUser/GetFriendList/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user
string Norelationship type (ex: friend)
GETGetPlayerBans
https://api.steampowered.com/ISteamUser/GetPlayerBans/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
string Yes Comma-delimited list of SteamIDs
GETGetPlayerSummariesv2
https://api.steampowered.com/ISteamUser/GetPlayerSummaries/v2/
NameValueTypeRequiredDescription
click to setstring Yes access key
string Yes Comma-delimited list of SteamIDs (max: 100)
PUBLISHERGETGetPublisherAppOwnershipv5
https://partner.steam-api.com/ISteamUser/GetPublisherAppOwnership/v5/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user
PUBLISHERGETGetPublisherAppOwnershipChanges
https://partner.steam-api.com/ISteamUser/GetPublisherAppOwnershipChanges/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
string Yes The unsigned 64-bit row version to read package changes from. The row version of data read up to will be returned for use in future calls.
string Yes The unsigned 64-bit row version to read CD Key changes from. The row version of data read up to will be returned for use in future calls.
GETGetUserGroupList
https://api.steampowered.com/ISteamUser/GetUserGroupList/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user
PUBLISHERPOSTGrantPackagev3
https://partner.steam-api.com/ISteamUser/GrantPackage/v3/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user
uint32 Yes PackageID to grant
string Noip address of user in string format (xxx.xxx.xxx.xxx).
string NoOptionally associate third party key during grant. 'thirdpartyappid' will have to be set.
uint32 NoHas to be set if 'thirdpartykey' is set. The appid associated with the 'thirdpartykey'.
GETResolveVanityURL
https://api.steampowered.com/ISteamUser/ResolveVanityURL/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
string Yes The vanity URL to get a SteamID for
int32 NoThe type of vanity URL. 1 (default): Individual profile, 2: Group, 3: Official game group
PUBLISHERPOSTRevokePackage
https://partner.steam-api.com/ISteamUser/RevokePackage/v1/
NameValueTypeRequiredDescription
click to setstring Yes access key
uint64 Yes SteamID of user
uint32 Yes PackageID to grant
string Yes Reason for why to revoke