Solidity `console.log()` reference

Hardhat allows you to print logging messages and contract variables by calling console.log() when running your Solidity code in a simulated network or a Solidity test.

To use it, simply import hardhat/console.sol and call it as if it were Node.js’ console.log. It implements the same formatting options, which in turn uses util.format.

For example, this contract prints a formatted string when it’s deployed:

contracts/ConsoleLogExample.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;

import "hardhat/console.sol";

contract ConsoleLogExample {
  constructor() {
    console.log(
      "msg.sender is %s and block number is %d",
      msg.sender,
      block.number
    );
  }
}

Supported functions

You can use console.log in any Solidity function, including view and pure.

Supported console.log overloads

You can call console.log with up to 4 parameters in any order of the following types:

• uint256
• string
• bool
• address

There are also single parameter functions for the types above, and additionally bytes, bytes1… up to bytes32:

• console.logInt(int i)
• console.logUint(uint i)
• console.logString(string memory s)
• console.logBool(bool b)
• console.logAddress(address a)
• console.logBytes(bytes memory b)
• console.logBytes1(bytes1 b)
• console.logBytes2(bytes2 b)
• …
• console.logBytes32(bytes32 b)

To check the most up-to-date version, refer to hardhat/console.sol in the version you have installed.

console.log in other tools and networks

If you accidentally deploy a contract with a console.log or use it in a tool that doesn’t support it, it won’t have any side effects when run, except for an increased gas cost.

This is because console.log works by sending static calls to a well-known contract address that has no code. At runtime, Hardhat detects calls to that address, decodes their input data, and writes it to the terminal.