Getting Started

Use the Chainlink Functions Starter Kit with Hardhat to set up your on-chain contracts, test your requests, and send your requests to be fulfilled by the Chainlink Functions Decentralized Oracle Network (DON). Chainlink Functions is available on Sepolia and Polygon Mumbai, but this guide uses Polygon Mumbai to simplify access to testnet funds. Complete the following tasks to get started with Chainlink Functions:

Set up your Web3 wallet and find your private key
Install the required frameworks
Configure the starter kit with your environment variables
Simulate a Chainlink Functions request
Set up a subscription for Chainlink Functions
Send a Chainlink Functions request to the DON

Set up your environment

You must provide the private key from a testnet wallet to run the examples in this documentation. Install a Web3 wallet, configure Node.js, clone the Starter Kit, and configure a .env file with the required variables.

Install and configure your Web3 wallet for Polygon Mumbai:

Install the MetaMask wallet or other Ethereum Web3 wallet.
Set the network for your wallet to the Polygon Mumbai testnet. If you need to add Mumbai to your wallet, you can find the chain ID and the LINK token contract address on the LINK Token Contracts page.
- Polygon Mumbai testnet
Request testnet MATIC from the Polygon Faucet.
Request testnet LINK from faucets.chain.link/mumbai.

Install the required frameworks and dependencies:

Install Node.js 18. Optionally, you can use the nvm package to switch between Node.js versions with nvm use 18.

Note: The starter kit only supports node versions at 18 or higher. To ensure you are running the correct version in a terminal, type node -v.
```
node -v
```
```
$ node -v
v18.7.0
```

In a terminal, clone the Chainlink Functions Starter Kit repository and change directories.

git clone https://github.com/smartcontractkit/functions-hardhat-starter-kit.git && \
cd functions-hardhat-starter-kit/

Run npm install to install the dependencies.
```
npm install
```
For higher security, the starter kit encrypts your environment variables at rest.
1. Set an encryption password for your environment variables.
```
npx env-enc set-pw
```
2. Run npx env-enc set to configure a .env.enc file with the basic variables that you need to send your requests to the Polygon Mumbai network.
  - POLYGON_MUMBAI_RPC_URL: Set a URL for the Polygon Mumbai testnet. You can sign up for a personal endpoint from Alchemy, Infura, or another node provider service.
  - PRIVATE_KEY: Find the private key for your testnet wallet. If you use MetaMask, follow the instructions to Export a Private Key. Set this in the .env file. Note: The Chainlink Functions hardhat starter kit uses your private key to sign any transactions you make such as deploying your consumer contract, creating subscriptions, and making requests.
```
npx env-enc set
```
Compile the contracts in the repository. You will see several compile warnings, but no errors.
```
npx hardhat compile
```

Simulate a request to test your environment and make sure everything is configured correctly. Run the npx hardhat functions-simulate command. The simulation runs on a local Hardhat network (a local Ethereum network node designed for development) and executes a request defined in the default Functions-request-config.js file. The starter kit includes the capability to simulate transactions so you can quickly test your code before you send it to the DON.

npx hardhat functions-simulate

If the simulation is successful, the output includes the simulated on-chain response:

__Simulated On-Chain Response__
Response returned to client contract represented as a hex string: 0x00000000000000000000000000000000000000000000000000000000000f50ed
Decoded as a uint256: 1003757

Gas used by sendRequest: 360602
Gas used by client callback function: 75029

Configure your on-chain resources

After you configure your local environment, configure some on-chain resources to process your requests, receive the responses, and pay for the work done by the DON.

Deploy an on-chain FunctionsConsumer.sol contract, create a subscription, and fund the subscription with LINK to pay for requests after they are fulfilled.

Deploy the consumer contract and record the contract address. For now, you can skip on-chain contract verification with the --verify false flag. If you do need to verify your contract on-chain, sign up for a free Polygonscan API key and include the key in your .env.enc file by running npx env-enc set and set POLYGONSCAN_API_KEY.
```
npx hardhat functions-deploy-client --network polygonMumbai --verify false
```
Find the contract address in the output:
```
FunctionsConsumer contract deployed to 0x4B4BA2Fd6b93aDF8d6b6002E10540E58394388Ea on mumbai
```
Create a Chainlink Functions subscription and add your contract as an approved consumer contract. You can do this with a single transaction if you include your contract address with the --contract flag. For this example, 1 LINK is more than enough on the Mumbai testnet. You can always get more LINK from faucets.chain.link and later add it to the subscription. See the Subscriptions Management page for details.
```
npx hardhat functions-sub-create --network polygonMumbai --amount 1 --contract YOUR_CONSUMER_CONTRACT_ADDRESS
```
Record the subscription ID from the output.
```
Created subscription with ID: 443
Owner: 0x9d087fC03ae39b088326b67fA3C788236645b717
Balance: 1.0 LINK
1 authorized consumer contract:
[ '0x4B4BA2Fd6b93aDF8d6b6002E10540E58394388Ea' ]
```

Run the example request

After your environment and on-chain resources are configured, you can send your request to the DON to execute the request defined in the Functions-request-config.js file. Run npx hardhat functions-request. Specify your subscription ID with the --subid flag and specify your consumer contract address with the --contract flag.

npx hardhat functions-request --subid YOUR_SUBSCRIPTION_ID --contract YOUR_CONSUMER_CONTRACT_ADDRESS --network polygonMumbai

The on-chain transaction and request will take longer to complete than the simulation. The output includes a decoded response:

Actual amount billed to subscription #443:
┌──────────────────────┬─────────────────────────────┐
│         Type         │           Amount            │
├──────────────────────┼─────────────────────────────┤
│  Transmission cost:  │  0.000074413446128386 LINK  │
│      Base fee:       │          0.2 LINK           │
│                      │                             │
│     Total cost:      │  0.200074413446128386 LINK  │
└──────────────────────┴─────────────────────────────┘


✔ Request 0x4b97078053700c816e6ba1cd54fa5a5b4c279f36c6e4a4be690a71ba84d26819 fulfilled! Data has been written on-chain.

Response returned to client contract represented as a hex string: 0x00000000000000000000000000000000000000000000000000000000000f50ed
Decoded as a uint256: 1003757

If your request is successful, you have all the tools that you need to make your own custom requests. Edit the Functions-request-config.js file and the calculation-example.js source file with your own code. Then, run the npx hardhat functions-request command again to test your changes. You can re-use the same consumer contract and subscription for different requests.

Chainlink Functions is capable of much more than just computation. Try one of the Tutorials to see examples that can GET and POST to public APIs, securely handle API secrets, handle custom responses, and query multiple APIs.

Getting Started

Set up your environment

Configure your on-chain resources

Run the example request

What's next

Stay updated on the latest Chainlink news