Deploy a Smart Contract Using Hardhat and Hedera JSON-RPC Relay
A step-by-step guide on deploying a smart contract to Hedera testnet and Hedera Local Node using Hardhat.
In this tutorial, you will walk through the step-by-step guide on deploying smart contracts using Hardhat and Hedera JSON-RPC Relay. Hardhat is a development environment for Ethereum. It consists of different components for editing, compiling, debugging, and deploying smart contracts and dApps, all working together to create a complete development environment.
The Hedera JSON-RPC Relay is an implementation of Ethereum JSON-RPC APIs for Hedera and utilizes both Hedera Consensus Nodes and Mirror Nodes to support RPC queries defined in the JSON-RPC Specification. The Hedera Local Node project enables developers to establish their own local network for development and testing. The local network comprises the consensus node, mirror node, JSON-RPC relay, and other Hedera products, and can be set up using the CLI tool and Docker. This setup allows you to seamlessly build and deploy smart contracts from your local environment.
By the end of this tutorial, you'll be equipped to deploy smart contracts on the Hedera Testnet or your local Hedera node, leveraging Hardhat's tools for testing, compiling, and deploying.
Prerequisites
Basic understanding of smart contracts.
Basic understanding of Node.js and JavaScript.
Basic understanding of Hardhat Ethereum Development Tool.
Step 1: Set Up Project
To simplify the setup process, you can clone a boilerplate Hardhat example project from the hedera-hardhat-example-project
repository. Open a terminal window and navigate to your preferred directory where your Hardhat project will be stored.
Run the following command to clone the repo, change into the directory, and install dependencies:
git clone https://github.com/hashgraph/hedera-hardhat-example-project.git
cd hedera-hardhat-example-project
npm install
Open the project in Visual Studio Code or your IDE of choice. The project structure of the repo you just cloned should look like this:
hedera-hardhat-example-project
├── node_modules
├── contracts
├── scripts
├── test
├── .env.example
├── .gitignore
├── hardhat.config.js
├── package-lock.json
├── package.json
└── README.md
Let's review the Hardhat project folders/content. For more information regarding Hardhat projects, check out the Hardhat docs. If you do not need to review the project contents, you can skip this optional step.
Step 2: Configure Project
In this step, you will update and configure your environment variables and Hardhat configuration files. These files play a crucial role in defining tasks, securely storing account private keys, and specifying RPC endpoint URLs required for network interactions.
Environment Variables
The .env
file securely stores environment variables, such as your Hedera network endpoints and private keys, which are then imported into the hardhat.config.js
file. This helps protect sensitive information like your private keys and API secrets, but it's still best practice to add .env
to .gitignore
file to prevent you from committing and pushing your credentials to GitHub. Go to the tab corresponding to your deployment path and follow the steps to set up your environment variables.
Rename the
.env.example
File Start by renaming the provided.env.example
file to.env
.Review the
.env
File Open the.env
file to modify with your private keys and understand its contents.
Prerequisite: A Hedera Local Node set up and running (setup tutorial).
Hedera Local Node environment variables
The variables are predefined for the purposes of this tutorial.
# Your Hedera Local Node ECDSA account alias private key
LOCAL_NODE_OPERATOR_PRIVATE_KEY=0x105d050185ccb907fba04dd92d8de9e32c18305e097ab41dadda21489a211524
# Your Hedera Local Node JSON-RPC endpoint URL
LOCAL_NODE_ENDPOINT='http://localhost:7546/'
Variables explained
LOCAL_NODE_OPERATOR_PRIVATE_KEY
: This is your Alias ECDSA hex-encoded private key for your Hedera Local Node. Replace the example value with your actual private key. Once you set up your local node and run the command to start, the accounts list for alias ECDSA private keys will be generated and returned to your console (see screenshot below). Replace the example value with your actual private key.

LOCAL_NODE_ENDPOINT
: This is the URL endpoint for your Hedera Local Node's JSON-RPC Relay. Typically, this would be yourlocalhost
followed by the port number (http://localhost:7546/
).

Configuring these environment variables enables your Hardhat project to interact with the Hedera network or your local node. Let's review the Hardhat configuration file, where these environment variables are loaded into.
Hardhat Configuration File
The Hardhat config (hardhat.config.js
) file serves as the central configuration file for your Hardhat project. This file is crucial for specifying various settings, including Hardhat tasks, network configurations, compiler options, and testing settings. Let’s review the configuration settings.
Required Packages and Mocha Settings
These first lines import the required Hardhat plugins and the dotenv
module that loads environment variables from the .env
file. This will allow you to keep your private keys secure while using them in your dApp and will keep you from committing these to GitHub.
require("@nomicfoundation/hardhat-toolbox");
require("@nomicfoundation/hardhat-chai-matchers");
require("@nomiclabs/hardhat-ethers");
require("dotenv").config(); // Import dotenv library to access the .env file
Hardhat Tasks
These lines define tasks that are accessed and executed from the test/
or scripts/
folders.
//define hardhat task here, which can be accessed in our test file (test/rpc.js) by using hre.run('taskName')
task("show-balance", async () => {
const showBalance = require("./scripts/showBalance");
return showBalance();
});
task("deploy-contract", async () => {
const deployContract = require("./scripts/deployContract");
return deployContract();
});
task("contract-view-call", async (taskArgs) => {
const contractViewCall = require("./scripts/contractViewCall");
return contractViewCall(taskArgs.contractAddress);
});
task("contract-call", async (taskArgs) => {
const contractCall = require("./scripts/contractCall");
return contractCall(taskArgs.contractAddress, taskArgs.msg);
});
Solidity Compiler Settings
Here, the Solidity compiler version is set to "0.8.9". The optimizer is enabled with 500 runs to improve the contract's efficiency.
/** @type import('hardhat/config').HardhatUserConfig */
module.exports = {
mocha: {
timeout: 3600000,
},
solidity: {
version: "0.8.9",
settings: {
optimizer: {
enabled: true,
runs: 500,
},
},
},
Network Configurations
The networks
object is essential for defining the Hedera networks your Hardhat project will connect to. Additionally, the defaultNetwork
key specifies the network Hardhat will default to if none is specified at deployment.
// Specifies which network configuration will be used by default when you run Hardhat commands.
defaultNetwork: "local",
networks: {
// Defines the configuration settings for connecting to Hedera local node
local: {
// Specifies URL endpoint for Hedera local node pulled from the .env file
url: process.env.LOCAL_NODE_ENDPOINT,
// Your local node operator private key pulled from the .env file
accounts: [process.env.LOCAL_NODE_OPERATOR_PRIVATE_KEY],
},
},
Key/value breakdown:
defaultNetwork
: This property specifies which network configuration will be used by default when you run Hardhat commands.networks
: This property contains configurations for different networks you might connect to.url
: This specifies the URL endpoint for the network. The value is pulled from the.env
file where the environment variables are defined.accounts
: This lists the private keys for the accounts you'll use when connecting to the network. The value is pulled from the.env
file where the environment variables are defined.
Step 3: Compile Contract
Now that your project is configured compile your contract. Run the following command in the hedera-hardhat-example-project
terminal:
npx hardhat compile
The compiled artifacts will be saved in the artifacts/
directory by default, or whatever your configured artifacts path is. The metadata file generated in this directory will be used for the smart contract verification process in a later step.

After the initial compilation, if you don't modify any files, nothing will be compiled when you run the compile
command. To force a compilation you can use the --force
flag or run npx hardhat clean
to clear the cache and delete the artifacts to recompile.
Step 4: Test and Deploy Contract
Once your contract is compiled successfully, deploy the Greeter.sol
smart contract. There are additional steps required if you're deploying to your local node:
Test
Test your contract before deploying it. In the hedera-hardhat-example-project
terminal, run the following command to compile and test your contract:
npx hardhat test
Tests should pass with "4 passing" returned to the console. Otherwise, an error message will appear indicating the issue.
Deploy
In the same terminal, run the following command to deploy your contract to the default network specified in your config file:
npx hardhat deploy-contract
Alternatively, you can target any network configured in your Hardhat config file. For testnet:
npx hardhat run --network testnet scripts/deployContract.js
Next Steps
Stop Local Node
Stop your local node and remove Docker containers by running hedera stop
or docker compose down
in your hedera-local-node
terminal. Reference the Stop Your Local Node section of the local node setup tutorial.
Deploy on Hedera Testnet
If you're up for it, follow the steps to deploy on the Hedera testnet and verify your contract.
Congratulations! 🎉 You have successfully learned how to deploy a smart contract using Hardhat and Hedera JSON-RPC Relay. Feel free to reach out in Discord!
Additional Resources
➡ Hedera Local Node Repository
➡ Hedera JSON-RPC Relay Repository
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