OpenSea Now Offers Options For IPFS And Metadata Freezing

OpenSea made a recent announcement outlining a new strategy that will allow its users to decentralize their NFT metadata using the Interplanetary File System (IPFS) as well as Filecoin. The new strategy also provides a way for collectors to see when the metadata for an NFT is immutable or not, further augmenting the toolkit that OpenSea collectors have at their disposal when valuing NFTs. 

When asked about their decision to add metadata freezing options to the toolkit, OpenSea explained they were out to “provide a source of truth for any non-fungible token regardless of the blockchain, metadata format, or decentralized storage solution used to implement it”—a goal they have been working towards since their inception back in 2017. 

Below we will reiterate OpenSea’s information on how it all works and why decentralizing metadata matters. After that, you can check out their help center tutorial if you want to learn how to decentralize your OpenSea-made NFTs.

Note: All information stated here has been repurposed from OpenSea’s original blog post. 

Decentralized vs frozen metadata

For Ethereum-based tokens, the smart contract that governs an NFT usually specifies the location of the metadata using a function:

-For the ERC721 standard: function tokenURI(uint256 _tokenId) external view returns (string memory)

-For the ERC1155 standard:  function uri(uint256 _id) external view returns (string memory)

The value returned by this function is often a URL in Google Cloud, Amazon Web Services, or some other form of centralized storage that can go offline or be mutated by the developer.

This is in contrast with decentralized storage solutions like IPFS, Filecoin, and Arweave, which replicate metadata across storage nodes in a decentralized network.

Centralized storage is subject to two weaknesses:

Impermanence: The server can go down or offline, making it hard to find the image (unless it was mirrored by an NFT index like OpenSea).

Mutability: The developer can modify the image to something a collector does not expect.
There are four types of metadata storage for NFTs. Here’s a handy grid:

The concept of “frozenness” is distinct from centralization. Even when they are stored in a decentralized manner, it’s often still possible for the creator to make a transaction and change the metadata associated with an NFT. We call NFTs that have unchangeable metadata “frozen”.

Without better visibility on which NFTs are frozen and which are not, collectors can’t know if what they’re buying will be the same in 1, 10, or 100 years.

Not all NFTs fit cleanly into just one quadrant. Let’s go through them with some examples:

Centralized: Most NFTs have a function on their smart contract to return the metadata associated with a particular token identifier. The result is often a URL on a web server run by the developer (e.g. example.com/nft/2). When the properties and media of an NFT are all controlled by a server like this, the NFT is centralized and will be subject to impermanence and mutability problems.

Centralized and verifiable: One of the earliest NFTs, CryptoPunks by Larva Labs, stores its images in a centralized server. However, the smart contract stores the hash of this image in the smart contract. This means that while CryptoPunks may be subject to impermanence, any modification to its images can be checked against this hash, so we can “verify” if a CryptoPunk image is original or modified.

Decentralized: Instead of storing metadata in a central server, developers have the option to store it directly in the smart contract or in a file-friendly decentralized network. Two of the best options are IPFS with Filecoin and Arweave.

Decentralized and frozen: It’s tricky to know when an NFT’s metadata is frozen or not, as there are usually multiple ways of changing it. This is a manual process, but OpenSea now shows when NFTs made on OpenSea have been frozen and when many NFTs outside of OpenSea is immutable as well. 

Note from OpenSea: Some projects store their metadata directly in the smart contract. For example, a different project by Larva Labs, Autoglyphs, returns character art directly from the contract and was the first NFT to do so. It does not depend on any other system aside from Ethereum to render the image, so we call it decentralized, on-chain, and (in this case) frozen.

There are benefits and drawbacks to all four approaches. But it’s helpful for collectors to know more about NFT implementation when making value-based decisions. That’s why we’re introducing a new event type to augment the ERC1155 and ERC721 standards so that developers can tell platforms like OpenSea when they intend to mark a specific NFT as “frozen”.

Permanent URLs

To solve the tension between frozen and unfrozen metadata, this new event will tell OpenSea to register a URI change as a “permanent” one, called PermanentURI. Here’s the event signature:

event PermanentURI(string _value, uint256 indexed _id);

After a PermanentURI event is emitted by an NFT smart contract, no one should be allowed to change the URI for the specific token ID again. More information is available in our docs. Like most standards in crypto, this is an ongoing development and subject to change based on community feedback.

OpenSea’s metadata freezing tutorial

To get started, head to your collection’s “Edit” page and press the pencil icon in the top right corner of one of your NFTs (you can find them under the search bar below the “Add New Item” button). Click the Freeze Metadata toggle, and you’ll see a window pop up, as shown below. Tick the box if you’re happy to proceed, then click Submit Transaction. While OpenSea doesn’t charge anything, you’ll need to pay a gas fee to save the new metadata URL to the smart contract:

Once you freeze an NFT, you cannot unfreeze it or change its metadata. It will be available for as long as Ethereum and Filecoin exist.

After you’ve frozen an NFT, you can view its IPFS URL directly from its OpenSea page. You can also view more information about how many Filecoin deals have been made for it using the NFT.Storage API in combination with your NFT’s IPFS content hash.