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.
UNDOCUMENTEDPOSTAddToWishlist
https://api.steampowered.com/IWishlistService/AddToWishlist/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
CUserInterface_NavData No
string No
string No
string No
string No
string No
uint32 No
string No
uint64 No
bool No
CUserInterface_CuratorData No
uint32 No
uint64 No
bool No
bool No
UNDOCUMENTEDPOSTAddWishlistItemCategory
https://api.steampowered.com/IWishlistService/AddWishlistItemCategory/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
uint64 No
string No
UNDOCUMENTEDGetItemCategories
https://api.steampowered.com/IWishlistService/GetItemCategories/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
https://api.steampowered.com/IWishlistService/GetSharedWishlistCategories/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
fixed64 No
string No

Get a user's wishlist.

https://api.steampowered.com/IWishlistService/GetWishlist/v1/
NameValueTypeRequiredDescription
uint64 Yes
https://api.steampowered.com/IWishlistService/GetWishlistCategories/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key

Get the number of items on a user's wishlist.

https://api.steampowered.com/IWishlistService/GetWishlistItemCount/v1/
NameValueTypeRequiredDescription
uint64 Yes
https://api.steampowered.com/IWishlistService/GetWishlistItemsOnSale/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
StoreBrowseContext No
string No
int32 No
string No
StoreBrowseItemDataRequest No
bool No
bool No
bool No
bool No
bool No
bool No
bool No
int32 No
bool No
bool No
bool No
bool No
bool No
StoreBrowseItemDataRequest No
bool No
bool No
bool No

Get a user's paginated wishlist applying various sorts and filters

https://api.steampowered.com/IWishlistService/GetWishlistSortedFiltered/v1/
NameValueTypeRequiredDescription
uint64 Yes
{message} Yes
{message} Yes If passed, item data will be returned
{enum} No
{message} Yes
int32 NoData in this range will be filled in with StoreBrowse data
int32 No
UNDOCUMENTEDPOSTRemoveFromWishlist
https://api.steampowered.com/IWishlistService/RemoveFromWishlist/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
https://api.steampowered.com/IWishlistService/RemoveWishlistItemCategory/v1/
NameValueTypeRequiredDescription
click to setstring Yes Access key
uint32 No
uint64 No