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.

Get information about recent offline messages and chats

https://api.steampowered.com/IFriendMessagesService/GetActiveMessageSessions/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 Noreturn only session information where a chat message has been sent since this time (for polling)
bool NoIf non-zero, return only message sessions that have messages since our message cutoff. If zero, we return all active sessions.
UNDOCUMENTEDGetRecentMessages

Get a log of recent chat messages between two users

https://api.steampowered.com/IFriendMessagesService/GetRecentMessages/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
fixed64 No
fixed64 No
uint32 NoIf non-zero, cap the number of recent messages to return.
bool NoGrab the block of chat from the most recent conversation (a ~5 minute period)
fixed32 NoIf non-zero, return only messages with timestamps greater or equal to this. If zero, we only return messages from a recent time cutoff.
bool NoReturn the results with bbcode formatting.
uint32 NoCombined with start time, only messages after this ordinal are returned (dedupes messages in same second)
uint32 Noif present/non-zero, return only messages before this.
uint32 No
https://api.steampowered.com/IFriendMessagesService/MarkOfflineMessagesRead/v1/
UNDOCUMENTEDPOSTResolveReport
https://api.steampowered.com/IFriendMessagesService/ResolveReport/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
fixed64 No
fixed64 No
uint64 No
uint64 No
int32 Noenum
int32 Noenum
bool No