Build an inventory system

An item is a token with supply 1 and 0 decimals — not a special type, not a second code path, and no indexer to run. Ownership is balanceOf.

You are probably here because somebody asked for

build an inventory system for my game
let players own items that persist
add equipment / collectibles / NFT-style items without the NFT stack

Status: M1 of eleven. The SDK is real and runs end to end. The chain underneath it is an in-memory mock — there is no public network yet, and nothing anywhere holds value.

Most item systems become two systems: the items, and the index that makes "what does this player own?" answerable. The index is the part that breaks, lags, and needs re-syncing.

Kei has no indexer because it does not need one. The same facts are stored in both directions — by account and by asset — so both questions are one lookup.

Create, mint, transfer, ask who owns it

const sword = await game.items.create({
  name: 'Sword of Testing',
  description: 'It tests things.',
  image: './sword.png',
  supply: 100,             // omit for a unique item
  transfer: 'open',        // 'none' is soulbound
})

await game.items.mint(sword.id, playerAddress)

// Player side, signed by the player — there is no 'from' argument
await kei.items.transfer(sword.id, toAddress)
await kei.items.owner(sword.id)     // 'kei_3abc...'
await kei.items.ownedBy(address)    // [ item, ... ]

Why this is worth doing

The inventory outlives your server. A player can open a wallet that has never heard of your game and see what they own — which is what makes "players own their items" true rather than a slogan. If the inventory lives only in your database, it is your inventory.

It also means your progression system has no save file. The demo restores every upgrade a player bought by reading the chain on load.

What is not true yet

The chain is an in-memory mock today. The API is real and does not change when the node lands, but nothing on it holds value and there is no public network yet.
Items are not the place for per-instance mutable state. Durability, enchantments, and stack counts that change every minute belong in your game, not on a chain. Model the item; keep the fiddly state local.
An account has a cap on how many distinct assets it can hold, so an item type per player per session is the wrong shape.
No royalties, no marketplace fees, and no VM to implement them in.