Multichain Counter — Base & Celo (mainnet, Remix)

Ultra-minimal Solidity Counter deployed on Base mainnet and Celo mainnet using Remix + MetaMask.
Verification via Sourcify (automatic) or manual Single file verification on the explorers.

Quick usage (ethers v6)

(async () => {
  if (!window.ethers) {
    await new Promise((res, rej) => {
      const s=document.createElement('script');
      s.src="https://cdn.jsdelivr.net/npm/ethers@6.12.0/dist/ethers.umd.min.js";
      s.onload=res; s.onerror=rej; document.head.appendChild(s);
    });
  }
  // Pick the address for the current network:
  // const COUNTER = "0xBB81C40eFe9BFcae6EE8B81383A88Bb2A4d04D0d"; // Base mainnet
  const COUNTER = "0xfe1ee5f62BA11f283FB9678D10aaA196e3EB331f";   // Celo mainnet

  const provider = new ethers.BrowserProvider(window.ethereum);
  await provider.send("eth_requestAccounts", []);
  const signer = await provider.getSigner();

  const abi = [
    "function increment(uint256)",
    "function value() view returns (uint256)",
    "event Increment(address indexed by, uint256 newValue)"
  ];

  const counter = new ethers.Contract(COUNTER, abi, signer);
  console.log("value =", (await counter.value()).toString());
  const tx = await counter.increment(1n);
  console.log("tx:", tx.hash);
  await tx.wait();
  console.log("value after =", (await counter.value()).toString());
})();

Contract

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

contract Counter {
    uint256 public value;
    event Increment(address indexed by, uint256 newValue);
    function increment(uint256 x) external {
        value += x;
        emit Increment(msg.sender, value);
    }
}

Deployments

Base (mainnet)

Contract: 0xBB81C40eFe9BFcae6EE8B81383A88Bb2A4d04D0d

Explorer: https://basescan.org/address/0xBB81C40eFe9BFcae6EE8B81383A88Bb2A4d04D0d

Tx increment(1): 0x507fcca75166d11c8c1007356f07358b385f5589400e8209205c5c207488f542 → https://basescan.org/tx/0x507fcca75166d11c8c1007356f07358b385f5589400e8209205c5c207488f542

Celo (mainnet)

Contract: 0xfe1ee5f62BA11f283FB9678D10aaA196e3EB331f

Explorer: https://celoscan.io/address/0xfe1ee5f62BA11f283FB9678D10aaA196e3EB331f

Tx increment(1): 0x33f6985005ca9d3abdfba6a140a69028758de4e47f61de0247bd45cb843185b3 → https://celoscan.io/tx/0x33f6985005ca9d3abdfba6a140a69028758de4e47f61de0247bd45cb843185b3

EOA used on both chains: 0x65a4b717D9950CC364aA37a89a78c2beF3559200

Reproduce in 1 minute (Remix)

Open https://remix.ethereum.org → create contracts/Counter.sol with the code above.

Compile Solidity 0.8.20, Optimizer ON (200).

Deploy & Run → Injected Provider – MetaMask → select Base → Deploy → confirm.

Call increment(1) → confirm → read value() (should be 1).

Switch to Celo → Deploy → increment(1) → read value().

Contract verification

Sourcify (Remix Sourcify plugin), or

Explorer → Verify & Publish → Single file

Compiler: 0.8.20

Optimizer: Yes, runs 200

Constructor args: none

Paste Counter.sol exactly as above