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Is it possible to somehow update an existing ERC-721 Token's MetaData after it was already minted?

Let's say we've created a Knight character for a game - by minting an NFT for it, and 3 months later we want to update that Knight's attributes to reflect the amount of experience or treasure it has amassed through game play.

The original URI for this Knight-Token looked something like this:

{  
    "name" : "KnightToken1",  
    "description" : "One-of-a-kind-Knight",
    "image" : "http://www.mydomain.com/myImages/knightImage.png”, 
    "attributes" : 
     {  
        “Age” : “30",
        "Treasure” : “2 Gold Crates”
     }

}

We now want to update the "Treasure" attribute to "100 Gold Crates" - how can it be done?

My understanding was that it can't be done - the Blockchain is supposedly immutable after all - but I've seen some posts essentially saying "with our API you CAN do this!" - except they don't tell you how.

So I'm wondering: is this a false claim - or is there really some clever way of updating an already-minted ERC-721's token metadata? And if so, how?

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Is it possible to somehow update an existing ERC-721 Token's MetaData after it was already minted?

Yes. This is not disallowed by the standard and so you are free to do this.

The official implementation of ERC-721 is maintained by 0xcert. It is free/open source and you can use the Metadata Mock contract as a starting point. You will simply add a public function that calls the internal _setTokenUri function which is waiting for you.

It will be up to you decide whether to allow anybody to change any URI anytime or if certain restrictions will be implemented.

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  • 4
    Oh interesting. Seems to set up a fun paradox: On the one hand, while we’d want the owner of any NFT to truly own it - it shouldn’t mean this ownership would permit them to freely change their Token’s metadata. Cause if they do they could set their Knight’s “Treasure” value to “50,000,000 Gold Crates” at will. On the other hand, if we, the developers, need to be able to update the “Treasure” attribute of said Knight-NFT - well, by definition we shouldn’t have permission to tweak the attributes of an NFT that is clearly owned by someone else. Cause that would break everything. Fun!
    – Mark55
    Sep 28, 2020 at 20:09
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    William, I looked at the ERC 721 code maintained by OpenZeppelin, and there doesn't seem to be a setTokenUri function. See here: github.com/OpenZeppelin/openzeppelin-contracts/blob/master/… OpenZeppelin contracts are popular for being compliant. Almost everyone uses them. Are you sure setTokenUri is not disallowed by the standard? Moreover any ideas why OpenZeppelin's implementation doesn't have it?
    – Hassan Baig
    Jul 27, 2021 at 15:02
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    I am quite sure that setting a token URI is not disallowed by the standard, you can consider me an authority on this topic. OpenZeppelin Contracts does allow this, please note the virtual modifier on the tokenURI definition. They do not implement it for you because they usually implement the most popular use case.
    – William Entriken
    Jul 28, 2021 at 2:12
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    _setTokenUri still exists here.
    – Sierox
    Oct 9, 2021 at 17:23
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    I think there's some confusion here about what is on-chain and off-chain and this answer only partially answers the question. You can set a new token uri in the contract OR you simply update the metadata json (if it is hosted on your server) that the token uri points to. I think this is what you really want.
    – phaze
    Dec 5, 2021 at 15:07
5

I created an NFT, listed it on OpenSea testnet. TestNFT

The NFT had a link to a json metadata file. After a few minutes, I edited the json metadata file, and then hit the refresh metadata button on opensea, and the metadata changed to the new value. So, yes, you can do this.

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