Your first smart contract in Remix

Education only. Not financial advice.

Education only. Not financial advice.

Watch the video

What you'll learn

• What a smart contract and Solidity are
• How to have Grok explain a contract line by line
• How to deploy and use a contract on Remix's in-browser test chain

Step 1: What is a smart contract?

Ethereum.org says: "A 'smart contract' is simply a program that runs on the Ethereum blockchain." (Ethereum.org smart contracts)

One language for writing them is Solidity. Its docs say: "Solidity is an object-oriented, high-level language for implementing smart contracts." (Solidity docs)

Step 2: Paste the counter contract into Remix

1. Open Remix in your browser.
2. In the File Explorer, create a new file named Counter.sol.
3. Paste this in:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

// A tiny practice contract. Test networks or the Remix VM only.
contract Counter {
    uint256 public count;          // the number we store

    function increment() public {  // add 1
        count += 1;
    }

    function decrement() public {  // subtract 1
        require(count > 0, "Count is already zero");
        count -= 1;
    }
}

Step 3: Ask Grok to explain it

Paste this into Grok, followed by the contract:

I'm a beginner. Explain this Solidity contract line by line in plain words.
What does "uint256" mean? What does "require" do? What happens if I call
decrement when count is 0? Keep it short. Here is the contract:

Look for: count stores a number, increment adds 1, and decrement refuses to go below zero with the message "Count is already zero".

Grok's real answer (our test run)

We ran this exact prompt through Grok (model grok-4.7) on Oct 30, 2026. Grok's answers change from run to run, so yours will differ. Quoted as Grok returned it, except where we mark [trimmed] and where we swapped dashes for commas to match our style.

This is a tiny counter. Anyone can add 1 or subtract 1, but it will not go below 0.

• The license line is only a comment. It does not change how the code runs.
• pragma solidity ^0.8.20 means “compile this with Solidity 0.8.20 or a newer 0.8 version.”
• contract Counter { ... } is the contract: the program stored on the chain.
• uint256 public count is the stored number. uint256 means a whole number from 0 up to a very large limit (no negatives). public makes a free reader so anyone can check count. It starts at 0.
• increment adds 1 to count. public means anyone can call it.
• decrement subtracts 1, but only after the check.
• require(count > 0, "Count is already zero") means “continue only if count is greater than 0.” If not, the call fails and that message is returned.

If you call decrement when count is 0, the require fails. The transaction reverts: nothing is saved, count stays 0, and you see "Count is already zero". In 0.8, subtracting from 0 would revert anyway; this check makes the reason clear.

Education only. Not financial advice.

Step 4: Compile and deploy on the test chain

1. Click the Solidity compiler icon and press the Compile button.
2. Click the Deploy & Run icon. Under Environment, pick Remix VM.
3. Press Deploy.

The Remix docs say: "The Remix VM is a sandbox blockchain in the browser. Transactions do not require an approval to run." (Remix docs: Deploy & Run) Everything here is play money.

Step 5: Click the buttons

Under Deployed Contracts, open Counter. 1. Press increment two times, then press count. You should see 2. 2. Press decrement one time, then count. You should see 1. 3. Press decrement two more times. The second one fails with "Count is already zero".

We tested this exact contract on a local test chain on our own computer: it compiled, the count read 1 after two increments and one decrement, and calling decrement at zero was refused.

Step 6: Don't write security code from scratch

OpenZeppelin Contracts calls itself "A library for secure smart contract development." and says: "Build on a solid foundation of community-vetted code." (OpenZeppelin Contracts docs) Our tip: when you're ready for real projects, start from well-known building blocks like these instead of inventing your own.

Want more practice? CryptoZombies teaches Solidity with a game.

Check yourself

1. What is a smart contract? (Answer: a program that runs on a blockchain)
2. Was the ETH in the Remix VM real? (Answer: No. It's play money in your browser.)
3. Why did the last decrement fail? (Answer: the require line stops count from going below zero)

Caution box Ethereum.org describes smart contracts as "running immutable logic based on code deployed on the blockchain." (Ethereum.org smart contract security) Immutable means it can't be changed, so a bug is hard to fix after launch. Our tip: keep your contracts on test networks or in the Remix VM while you learn. Education only. Not financial advice.

Builds on

• Lesson A3: Build with Grok as your coding partner
• Lesson C1: Blockchain basics: wallets and seed phrases

Sources

• Ethereum.org smart contracts: https://ethereum.org/en/developers/docs/smart-contracts/
• Ethereum.org smart contract security: https://ethereum.org/en/developers/docs/smart-contracts/security/
• Solidity docs: https://docs.soliditylang.org/
• Remix docs, Deploy & Run: https://remix-ide.readthedocs.io/en/latest/run.html
• OpenZeppelin Contracts docs: https://docs.openzeppelin.com/contracts/5.x/
• CryptoZombies: https://cryptozombies.io/

Creator credits

• xAI (Grok): X https://x.com/grok , https://x.com/spacexsi
• Ethereum.org: X https://x.com/ethdotorg
• Solidity: X https://x.com/solidity_lang
• Remix: X https://x.com/EthereumRemix , YouTube https://www.youtube.com/@EthereumRemix
• OpenZeppelin: X https://x.com/OpenZeppelin
• CryptoZombies: X https://x.com/CryptoZombiesHQ

Education only. Not financial advice.

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