Gnosis: Soulbound token with Remix and OpenZeppelin

TLDR:

• Soulbound tokens are non-transferable ERC-721s, enforced via a transfer override, so they can only be minted or burned.
• This tutorial covers creating and deploying a soulbound token contract on the Gnosis Chain Chiado testnet through a Chainstack node.
• You’ll use Remix for development, MetaMask for signing, and Blockscout to verify and interact with the contract.
• Minting a token assigns it to an address, and that address alone can burn it, ensuring the token never changes ownership.

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Main article

Soulbound tokens, originally proposed by Vitalik Buterin, at their core are simply non-transferable NFTs. In this tutorial, you will:

• Create an ERC-721 contract that has a transfer override to make the token soulbound.
• Deploy the contract on the Gnosis Chain Chiado testnet through a node deployed with Chainstack.
• Interact with the deployed contract.

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Prerequisites

• Chainstack account to deploy a reliable Gnosis Chain RPC endpoint.
• Remix IDE to compile the contract and deploy through MetaMask.
• MetaMask to deploy the contract through your Chainstack node and interact with the contract.

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Overview

To get from zero to a deployed soulbound token contract on the Gnosis Chain Chiado testnet, do the following:

1. With Chainstack, create a public chain project.
2. With Chainstack, join Gnosis Chain Chiado testnet.
3. With Chainstack, access your Gnosis Chain node credentials.
4. Set up your MetaMask to work through a Chainstack node.
5. With Remix IDE, create and compile the soulbound contract.
6. With Remix IDE, deploy the contract on the Gnosis Chain Chiado testnet.
7. Issue a soulbound token and burn it.

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Step-by-step

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Create a public chain project

See Create a project.

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Join the Gnosis Chiado testnet

See Join a public network.

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Get your Gnosis Chain node access and credentials

See View node access and credentials.

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Set up MetaMask

See Gnosis Chain tooling: MetaMask.

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Create and compile the soulbound contract

1. Open Remix IDE.
2. On the home page, click Environments > Solidity.
3. On the left pane, click File explorers > contracts > New File.
4. In the modal, give any name to your contract. For example, soulbound.sol.
5. Put in the contract code:
   // SPDX-License-Identifier: MIT
   pragma solidity ^0.8.7;
   
   import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
   import "@openzeppelin/contracts/utils/Counters.sol";
   import "@openzeppelin/contracts/access/Ownable.sol";
   
   contract SoulBoundToken is ERC721, Ownable {
       using Counters for Counters.Counter;
   
       Counters.Counter private _tokenIdCounter;
   
       constructor() ERC721("SoulBoundToken", "SBT") {}
   
       function safeMint(address to) public onlyOwner {
           uint256 tokenId = _tokenIdCounter.current();
           _tokenIdCounter.increment();
           _safeMint(to, tokenId);
       }
   
       function burn(uint256 tokenId) external {
           require(ownerOf(tokenId) == msg.sender, "Only the owner of the token can burn it.");
           _burn(tokenId);
       }
   
       function _beforeTokenTransfer(address from, address to, uint256) pure override internal {
           require(from == address(0) || to == address(0), "This a Soulbound token. It cannot be transferred. It can only be burned by the token owner.");
       }
   
       function _burn(uint256 tokenId) internal override(ERC721) {
           super._burn(tokenId);
       }
   }
   
   This is your soulbound token contract:
   • It uses the audited OpenZeppelin libraries to make the contract of the ERC-721 standard, belonging to the deployer, and increments each issued token ID by 1.
   • The contract has a modification to prohibit the token transfer, which makes the issued tokens soulbound.
   • The contract also implements a burn function to allow the owner of the issued token to be able to burn it.
6. Compile the contract. On the left pane, click Solidity compiler > Compile.

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Fund your account

Fund the account that you will use to deploy the contract with xDAI. Use the xDAI testnet faucet.

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Set up Remix IDE to work through your Chainstack node

On the left pane, click Deploy and switch to Injected Provider - MetaMask.

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Deploy the soulbound contract

On the left pane:

1. Click Deploy & run transactions.
2. In contract, select contracts/soulbound.sol.
3. Click Deploy.

This will engage your MetaMask to deploy the contract to the Gnosis Chain Chiado testnet through your currently selected MetaMask account. Click Confirm in the MetaMask modal.

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Interact with the contract

Once your contract is deployed, you can view it online at Blockscout Gnosis Chain Chiado testnet explorer. You are now going to verify the contract in the Blockscout explorer to be able to use the explorer as a web app and easily interact with the contract online.

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Flatten your contract code

Since your soulbound contract uses imported OpenZeppelin libraries, you must put all the imports into one .sol file to make Blockscout be able to verify it.

1. In your Remix IDE, click Plugin manager > Flattener > Activate.
2. Click Flattener > Flatten contracts/soulbound.sol.

The flattened contract is now in your clipboard.

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Verify the deployed contract on Blockscout explorer

1. Go to Blockscout explorer.
2. Find your deployed contract. The address of your contract is on the left pane of Remix IDE under Deployed Contracts.
3. On the contract page on Blockscout, click Code > Verify & Publish.
4. Select Via flattened source code.
5. In Contract Name, provide the name of your contract. In our example, the name is SoulBoundToken.
6. In Compiler, select the same compiler version that was used in Remix IDE.
7. In Optimization, select No.
8. In Enter the Solidity Contract Code, paste the flattened contract code.
9. Click Verify & publish. Blockscout will take a few seconds to compile your contract, verify, and publish it.

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Issue a soulbound token

Now that your soulbound contract is verified, you can check Blockscout to interact with it.

1. On Blockscout, on your contract, click Write Contract.
2. In your MetaMask, make sure you have the same address selected as the one that deployed the contract.
3. Click Connect wallet. This will connect your MetaMask instance with the contract owner as the active address.
4. In safeMint, provide an address that you own and to which you will issue a soulbound token.
5. Click Write.

This will issue a soulbound token to the provided address.

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Burn the soulbound token

Now that your other account has a soulbound token, you can burn it. In your MetaMask instance, switch to the account that has a soulbound token tied to it.

1. On Blockscout, on your contract, click Write Contract.
2. In your MetaMask, make sure you have the address selected that owns the issued soulbound token.
3. Click Connect wallet. This will connect your MetaMask instance with the token owner as the active address.
4. In burn, provide the token ID. If this is the first issued token, the ID is 0.
5. Click Write.

This will send the soulbound token from the current owner to the address 0x0000000000000000000000000000000000000000.

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Conclusion

This tutorial guided you through the basics of creating and deploying a simple soulbound contract on the Gnosis Chain Chiado testnet through your Chainstack-deployed node. You have also interacted with the contract, issued, and burned the token using Blockscout as a web app and MetaMask as your interaction tool that works through your Chainstack-deployed Gnosis Chain node.

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