6. Create NFT metadata

As stated earlier in the introduction, the Immutable Runner game features the fox and skins that players can unlock as NFTs.

In this section, you will:

1. Host the images for these NFTs.
2. Create JSON files that describe each NFT collection.
3. Create a simple JSON server to store the information for each NFT.

⚠️Warning

It is recommended to use services like AWS to host NFT metadata for better performance in production. The free services we will use in this section are adequate to demonstrate the necessary steps to create NFTs for a game.

Host NFT images on Pinata

Pinata is a service that enables users to host files on the InterPlanetary File System (IPFS) network. You can use Pinata to store NFT images, which ensures that the file's authenticity can be verified and that the file will always be publicly accessible.

You can use the NFT images we have already hosted on Pinata:

• Immutable Runner Fox NFT image
• Immutable Runner Skin NFT image

Typically, a unique image is generated for each NFT. However, for the purpose of this tutorial, we will use the same image for all fox NFTs, as well as for all skin NFTs. This simplifies the process and allows you to focus on the key steps.

If you want to host your images on Pinata, refer to the collapsible section below for instructions.

How to host images on Pinata

1. Sign up for a free account with Pinata.
2. Prepare an image for the fox and another for the skin.
   • Typically, a unique image is generated for each NFT. However, for this tutorial, you will use the same image for all fox NFTs, as well as for all skin NFTs.
3. In the Files tab, click Upload and then File.

4. Select the image for the fox and click Upload.

5. Repeat steps 3 and 4 for the skin.

💡Image URL

To get the URL of a file on Pinata, click on the file name to open it in a new tab. Then, copy the URL to use as needed.

Create NFT collection JSON files

💡Note

This is referred to as Contract URI from the Immutable Hub

Next, you’ll need a JSON file for each NFT collection which details the name, description and image of the collection.

You can use the NFT images we have already hosted on Pinata:

• collection_fox.json
• collection_skin.json

If you want to host your JSON files on Pinata, refer to the collapsible section below for instructions.

How to host JSON files on Pinata

1. Create two JSON files with the following format:

collection_fox.json

{
  "name": "Immutable Runner Fox",
  "description": "A collection of foxes for Immutable Runner",
  "image": "https://rose-ministerial-termite-701.mypinata.cloud/ipfs/Qmd3oT99HypRHaPfiY6JWokxADR5TzR1stgonFy1rMZAUy",
  "external_link": "https://immutable.com"
}

collection_skin.json

{
  "name": "Immutable Runner Skin",
  "description": "A collection of skins for Immutable Runner",
  "image": "https://rose-ministerial-termite-701.mypinata.cloud/ipfs/QmNZeG8wkW3mFw4PrqEj34NPA88impcvemYjhAkJAM4YcK",
  "external_link": "https://immutable.com"
}

2. Save the file as collection_fox.json and collection_skin.json.
3. Return to the Pinata Files tab and upload the two JSON files you created.

The fox and skin NFT collection metadata files are ready for step 7.

Create a server for hosting NFT metadata

NFTs use metadata to describe the unique properties of each token. This can include its name, description, attributes, image links, and other relevant data. All of this information is then stored in JSON files that follow a specific format.

To locate an NFT's metadata, a combination of a baseURI and the tokenID is used. This combination directs to the location of that particular NFT JSON file.

• The baseURI is specified in a smart contract at the deployment time (will be covered in step 7). In standard collection implementations, all NFTs belonging to a collection will have the same baseURI.
• The tokenID is generated during the minting process, and when appended to the baseURI will provide the unique location of an NFTs metadata.

For instance, if the fox NFT has a baseURI of https://immutable-runner.immutable.com/fox/ and an ID of 1, the metadata URL will be https://immutable-runner.immutable.com/fox/1. You can read more about this here.

In Immutable Runner, every new player is eligible to receive a unique fox NFT, and any player can also craft skin NFTs later in the game. As a result, the number of NFTs minted can increase rapidly. To simplify the process of creating metadata JSON files for each NFT, you can set up a server that automatically generates these files.

Have a look at the json-server/ folder. We've already provided a simple server code that generates the JSON metadata for the fox and skin NFTs.

💡Note

Some parts of the tutorial are not within scope, so the finished code has been added to the repository. It's recommended that you review the existing code to understand how you may implement it.

Try to run the server by doing the following:

1. cd json-server
2. yarn install
3. yarn start
4. Go to your browser and enter http://localhost:3000/fox/8 to see the metadata of fox NFT ID 8.
5. Enter http://localhost:3000/skin/2 to see the metadata of skin NFT ID 8.

You can update the skinImageUrl and foxImageUrl defined in json-server/src/index.ts to the URL of the images you uploaded to Pinata.

Set up Render

The metadata server must be live to ensure that the NFT metadata appears in the block explorer when a new asset is minted. In this tutorial, you use Render to host the metadata server.

1. Create a new repository in your GitHub account for the JSON server. You can name it immutable-runner-json-server and make it private.
2. Follow the GitHub instructions to set up the repository on your machine.
3. Copy all the files and folders located in the json-server/ directory to the new repository and push your code to GitHub.
4. Sign up to Render.
5. Click New + and select Web Service.

6. Select Build and deploy from a Git repository.

7. Connect your GitHub account.
8. Connect the repository you created.
   • You may need to configure your GitHub account to provide Render access to your repository.

9. Select Free for the Instance Type.

10. Click Create Web Service.
11. Render will deploy, build, and start your server. Once ready, you should see a live event in the Events tab.

You can now access the metadata of your NFTs by using the base URL provided in the header. such as https://immutable-runner-json-server.onrender.com/fox/10 or https://immutable-runner-json-server.onrender.com/skin/2.

This base URL will be used when you create and deploy NFT (ERC721) contracts in step 7.

⚠️Warning

You can use the free version of Render for this tutorial, but if you plan to use Render for production, consider upgrading to a paid account for better performance.