NFT Standard

Kalao respects the ERC-721 and ERC-1155 token standards. These are open standards that describe how to build non-fungible tokens on the blockchain. They require your smart contract to return a URI where Kalao can find the NFT metadata. For this, we use the tokenURI function. The contract should return an HTTPS or IPFS URL, which in turn should return a JSON blob of data with the metadata for your token.

The metadata can hold additional properties such as a name, description, and an image.

Metadata structure

Kalao supports metadata that is structured according to the official ERC-721 standard:

The Kalao marketplace supports different file formats including images, audio and videos. Each NFT has the following properties:

Image and Animation URL

URL to the image/video/audio file of the NFT. Either IPFS URL or file path.

Images Supported formats: JPG/PNG/GIF/WEBP

Recommended size for images: 500x500 px

Videos Supported formats: MP4, M4V, WEBM

Audio Supported formats: MP3, WAV

Maximum file size: 30MB

External URL

The URL which will appear below the asset's image on Kalao and allows users to view the item on your site.


A description of the NFT.


Name of the NFT.


These are the attributes for the NFT, which will show up on the NFT page.

Metadata example

When creating an NFT on the Kalao marketplace, you will be able to add a name, a description, properties and other information, as well as create a collection to group together related NFTs.

You will be able to view the metadata after creating the NFT.

The metadata is written into the code:

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