Define item definitions in the Steam Item Definition schema for your app, specifying type, name, description, and any bundle or exchange rules
Use the AddItem or AddPromoItem Web API method under IInventoryService to grant a specific itemdefid to a target Steam user by their SteamID64
Include a required requestid (a unique idempotency key per grant) to prevent duplicate grants if the call is retried
Parse the response to obtain the new item's itemid for tracking purposes
To revoke or consume an item, call the ConsumeItem method with the user's SteamID64, itemid, and the quantity to consume
Audit grants and consumptions periodically using the GetInventory method to reconcile server state with the Steam Inventory Service
Known gotchas
The requestid field is required for grant calls and must be unique per logical grant operation — reusing a requestid will return the original grant result without creating a new item
Item definitions must be published to the Steam Item Definition schema before they can be granted; unpublished defs will return an error
IInventoryService methods require a Steamworks publisher API key; using an application-level key without publisher permissions will fail authorization
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp