# Metadata

### Token URI

To pull in off-chain metadata for ERC721 NFTs, your contract need to return a URI where we can find the metadata. To find this URI, we use the `tokenURI` method in ERC721.

A tokenURI function may look something like this in your contract:

```
/**
 * @dev See {IERC721Metadata-tokenURI}.
 */
function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
    require(_exists(tokenId), "ERC721URIStorage: URI query for nonexistent token");

    string memory _tokenURI = _tokenURIs[tokenId];
    string memory base = _baseURI();

    // If there is no base URI, return the token URI.
    if (bytes(base).length == 0) {
        return _tokenURI;
    }
    // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
    if (bytes(_tokenURI).length > 0) {
        return string(abi.encodePacked(base, _tokenURI));
    }

    return super.tokenURI(tokenId);
}



```

Ultimately, the function needs to return an http or IPFS url, which returns a JSON object containing the metadata for the token queried.

### Metadata structure

```
{
  "description": "My project or NFT description.",
  "image": "https://mystorageapi/image", 
  "animation_url": "https://thisismyvideo.mystorage.com", 
  "name": "My NFT Name",
  "attributes": [ ... ], 
}
```

### Attributes

![](/files/7jLeaZLDQCsAjnifoRco)

```
{
"attributes": [
    {
      "trait_type": "Background", 
      "value": "Orange"
    }, 
    {
      "trait_type": "Eye Color", 
      "value": "Blue"
    }, 
    {
      "trait_type": "Face", 
      "value": "Casual Smile"
    }, 
    {
      "trait_type": "Shell", 
      "value": "Corn Tortilla"
    }, 
    {
      "trait_type": "Filling", 
      "value": "Beef"
    }
  ]
}
```

`trait_type` is the name of the trait, `value` is the value of the trait. Values are of type `string` (aka text between quotes).

### IPFS

If you use [IPFS](https://ipfs.io/) to host your metadata, your URL should be in the format `ipfs://<hash>`.


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