What is an object ID, and how do I find one?

An object ID is the globally unique 32-byte identifier of a Sui object, written as 64 hex characters with a 0x prefix. It's derived from the digest of the transaction that created the object plus a counter, and it never changes, even when the object is transferred, wrapped or modified. To find one, list your objects with sui client objects, read the created objects in a transaction's effects, search an explorer, or query it from the TypeScript SDK.

Find object IDs with the CLI

Terminal

# All objects owned by the active address (or pass an address or alias)
sui client objects

# Details for one object: type, owner, version, digest and fields
sui client object 0x<OBJECT_ID>

# Only your SUI coins
sui client gas

When you publish or call a function, the CLI output lists the object changes of the transaction. Look for created objects there: the package ID after a publish, a shared object made in init, or an UpgradeCap. Add --json to get machine-readable output for scripts.

Find object IDs from a transaction (TypeScript)

The created objects are in the effects. With @mysten/sui v2:

TypeScript

import { SuiGrpcClient } from '@mysten/sui/grpc';
import { Transaction } from '@mysten/sui/transactions';

const client = new SuiGrpcClient({
  network: 'testnet',
  baseUrl: 'https://fullnode.testnet.sui.io:443',
});

const tx = new Transaction();
tx.moveCall({ target: `${PACKAGE_ID}::counter::create` });

const result = await client.signAndExecuteTransaction({
  signer,
  transaction: tx,
  include: { effects: true, objectTypes: true },
});
if (result.$kind === 'FailedTransaction') throw new Error('transaction failed');

const { effects, objectTypes } = result.Transaction;
for (const obj of effects.changedObjects) {
  if (obj.idOperation === 'Created') {
    console.log(obj.objectId, objectTypes[obj.objectId]);
  }
}

To list what an address owns, optionally filtered by type:

TypeScript

const { objects } = await client.listOwnedObjects({
  owner: '0x<ADDRESS>',
  type: `${PACKAGE_ID}::counter::Counter`,
});
objects.forEach((o) => console.log(o.objectId, o.version));

Get an object's ID inside Move

Move

let id: ID = object::id(&counter);         // ID of any `key` value
let addr: address = counter.id.to_address(); // the same bytes as an address
let inner: ID = counter.id.to_inner();       // from a UID field

UID is the field type inside your struct and can't be copied or dropped. ID is a plain copyable value for storing references to other objects, emitting in events, or comparing.

Well-known IDs

Some system objects have fixed IDs on every network:

ID	Object
`0x5`	Sui system state
`0x6`	`Clock` (see How do I get the current time in Sui Move?)
`0x8`	`Random`
`0x403`	Coin deny list

Short forms like 0x6 are padded with leading zeros to the full 32 bytes. The SDK exports these as constants such as SUI_CLOCK_OBJECT_ID from @mysten/sui/utils.

Gotchas

Object ID vs. address. IDs and account addresses share the same 32-byte format and never collide. That's what lets you send objects to an object (transfer to object).
Wrapped objects disappear from lookups. Once an object is stored inside another object's field, a query by its ID won't find it until it's unwrapped. Dynamic object field children stay visible.
Package ID is an object ID too. A published package is an immutable object, and its ID is what you use in target strings (What is a package ID?).
Explorers work too. Paste an ID into any Sui explorer to see its owner, fields and history.

Sources

Object Model, Sui documentation
Address-Owned Objects, Sui documentation
object.move, Sui framework source
client_commands.rs, Sui CLI source