General

How is asset custody managed in Immutable X?

Immutable X is a self-custodial protocol, meaning all users are responsible for their own security. Users can manage their own private keys and maintain full control of their own assets, or opt for a custodial wallet flow. Users can deposit and withdraw their assets to and from the protocol at any time. Every transaction requires a signature from the user, and Immutable can’t authorise any actions on behalf of the user.

Does Immutable X have a block explorer? How do I keep track of user inventories?

Immutascan is a block explorer where Immutable X transactions can be viewed.

We also have API endpoints that are available for you to listen on. We recommend polling our mints, transfers, trades, etc endpoints at regular intervals to listen on events within Immutable X, and these endpoints can be filtered depending on your requirements.

How do I port or build smart contract logic on Immutable X?

This is not supported at the moment, though most NFT projects don’t have a need for general computation. For example, game-related NFTs can have off-chain events and interactions within the client’s application, and only need to interact with Immutable X for minting, transferring, burning, updating metadata, etc. A current limitation of ZK-rollups is general computation, but this challenge is rapidly being addressed by our partner StarkWare.

Metadata

For detailed information on metadata, please refer to our docs: https://docs.x.immutable.com/docs/asset-metadata

How does Immutable X handle metadata?

There are two types of metadata handled in Immutable X - mutable and immutable. Immutable metadata refers to the blueprint (see ‘What is the blueprint?’) that is defined at the time of minting to Immutable X, and this represents the on-chain metadata that will be passed to your Layer 1 smart contract at the time of withdrawing. Mutable metadata is the off-chain metadata that you provide through your metadata api, and is used in Immutable X to display all the properties and attributes of the asset.

How should I set up my metadata api endpoint?

When registering your contract with Immutable X, you need to provide a metadata api endpoint for us to retrieve metadata properties for each of your NFTs. We have a metadata crawler that attempts to find the metadata for every newly minted NFT by querying <metadata_api_url>/<client_token_id>, so please ensure that the metadata endpoint that you give us matches this format.

Your metadata endpoint should be able to handle a large amount of requests depending on the volume of your mints, and if it fails to provide a response to the crawler after a few retries or gets rate limited, then your assets may show up without metadata. The url must also be a valid https url, and if you are using IPFS then you should look into dedicated (not public) IPFS gateways.

Is it possible to update the metadata of an ERC721 token while it is on in Layer 2?

It is not possible to update immutable metadata (blueprint) of an NFT that has been minted to L2 as this is trustlessly passed to the Layer 1 smart contract when withdrawing (alongside the client token ID). However you are able to update mutable metadata by changing the data returned by your metadata api. Currently, our metadata crawler only runs once at the time of minting, so any changes to the off-chain metadata that we retrieve from your endpoint will have to be communicated to our Customer Success team so it can be updated on Immutable X. If you intend to refresh metadata after the collection is minted you will need to have approval from the Customer Success team in advance of your initial mint. We are working on making this process entirely self-service.

Minting

How do I start minting on Immutable X?

You will first need a deployed NFT smart contract on mainnet Ethereum that implements the mintFor function (see https://docs.x.immutable.com/docs/minting-assets-1). Then you will need to register your smart contract with Immutable X. Currently (September 2021), to register a minting contract, you must fill out the minting registration form (available here). We are close to rolling out self-serve contract registration for Immutable X, so soon you will be able to register your own contracts.

What is the blueprint?

The blueprint is a required field defined at the time of minting on Immutable X for each NFT. This represents the on-chain immutable metadata of the NFT that will be written to the blockchain when it is withdrawn from Immutable X. The blueprint string can be of any format you wish (but not empty), and it can typically look like a comma delimited string (e.g. "100,water,2,3"). This is passed to the mintFor function in your smart contract, in which you can implement custom logic to decode it on-chain or just save it as it is. You can have a look at our smart contract templates (https://github.com/immutable/imx-contracts) to get a better understanding of how the blueprint is used. You should aim to store as little data as possible on-chain to uniquely identify the value of the NFT (e.g. rarity, character_type).

Orders

Does Immutable X automatically match buy and sell orders for NFTs of the same value?

There is currently no automatic matching of orders as Immutable X only supports the maker/taker model at present. An NFT will be listed for sale for a specified price by the maker, and the trade occurs when this order is accepted by the taker. This will change in the future as we are working on implementing metadata orders where you can place buy orders on metadata properties (e.g. name = Demogorgon), which will bring more liquidity to functionally identical NFTs.

Can I authorize others to create buy/sell orders on my behalf?

Immutable X is a self-custodial protocol, and every transaction requires a signature from the owner of the wallet. No third party (including us) can touch your assets unless they have access to your private key.

NFTs

Is it possible to transfer assets between Immutable X and Ethereum freely?

Absolutely, that’s a key benefit of being a Layer 2 scaling solution. Even if Immutable X (the company) ceases to exist, users will always have the ability to withdraw all assets back to mainnet. Currently the Immutable X marketplace has yet to implement the withdrawals of NFTs on our frontend, however it is possible to withdraw NFTs using the Immutable X APIs.

If I mint an NFT on Immutable X, does it exist on-chain? What happens when I withdraw to mainnet?

If your NFT started off on mainnet Ethereum and was deposited into Immutable X, the asset will be locked in our L1 smart contract and will now be tradable on L2. When the asset is successfully withdrawn, The asset is released from the smart contract and sent to the withdrawing user’s wallet.

If your NFT was minted directly on to Immutable X (for no gas cost!), the asset will have Layer 1 representation, immutability, and cryptographic security via the merkle tree construct, but won’t be an ERC721 on mainnet ethereum until withdrawn from Immutable X. At the time of withdrawal, the asset will be minted onto L1.

Smart Contracts

Does Immutable X support ERC-1155s?

No, Immutable X does not support or recommend the use of ERC1155. We recommend that you use as few smart contracts as possible and consider merging your smart contracts, differentiating NFTs with metadata rather than by which smart contract they originated in.
Immutable X supports ERC721 smart contracts and recommends that you create a new ERC721 contract for each meaningfully different type of asset.


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