Hello World

Change and read a greeting field on Flow Testnet.

🚩 Quickstart 0: Hello World

🎫 Deploy a simple HelloWorld contract to learn the basics of the Flow blockchain and Cadence. You’ll use:

  • The local Flow emulator to deploy smart contracts.
  • The local Flow dev wallet to log into test accounts.
  • A template Next.js app with sample scripts and transactions to interact with your contract.

🌟 The final deliverable is a DApp that lets users read and change a greeting field on Flow testnet.

πŸ’¬ Meet other builders working on this challenge and get help in the Emerald City Discord!

πŸ“Ή Video Walkthrough

Want a video walkthrough? Check out Jacob Tucker’s walkthrough here:

πŸ“¦ Checkpoint 0: Install


  • Git
  • Node (🧨 Use Node v16 or a previous version as v17 may cause errors 🧨). You know you have installed it if you type node -v in your terminal and it prints a version.
  • Flow CLI (🧨 Make sure to install the correct link for your system 🧨). You know you have installed it if you type flow version in your terminal and it prints a version.
			git clone https://github.com/emerald-dao/0-hello-world.git

in a terminal window, πŸ“± install the dependencies start your frontend:

			cd 0-hello-world
npm install
npm run dev

in a second terminal window, start your πŸ‘·β€ local emulator:

			cd 0-hello-world
flow emulator start -v

Note: the -v flag means to print transaction and script output to your local emulator

in a third terminal window, πŸ’Ύ deploy your contract and πŸ’Έ start your local wallet:

			cd 0-hello-world
flow project deploy
flow dev-wallet

You can flow project deploy --update to deploy a new contract any time.

πŸ“± Open http://localhost:3000 to see the app

πŸ‘› Checkpoint 1: Wallets

We’ll be using the local Flow dev wallet.

Click the β€œLog In” button and notice a window appears with different accounts to select, each with their own Flow Token balance. Select the first account to log in to it.

πŸ“˜ Checkpoint 2: Reading the Greeting

πŸ‘€ Click the Get Greeting button to see your greeting:

get greeting

✏️ Checkpoint 3: Changing the Greeting

✏️ Change the greeting! Type a new greeting into the input and click the Change Greeting button. You should see a transaction pop up:

transaction popup

πŸ‘€ Click β€œAPPROVE” and then click the Get Greeting button again. You should now see your new greeting:

new greeting

πŸ’Ύ Checkpoint 4: Deploy it to testnet!

πŸ“” Ready to deploy to a public testnet?!?

πŸ” Generate a deployer address by typing flow keys generate --network=testnet into a terminal. Make sure to save your public key and private key somewhere, you will need them soon.

generate key pair

πŸ‘› Create your deployer account by going to https://testnet-faucet.onflow.org/, pasting in your public key from above, and clicking CREATE ACCOUNT:

configure testnet account on the website

After it finishes, click COPY ADDRESS and make sure to save that address somewhere. You will need it!

⛽️ Add your new testnet account to your flow.json by modifying the following lines of code. Paste your address you copied above to where it says β€œYOUR GENERATED ADDRESS”, and paste your private key where it says β€œYOUR PRIVATE KEY”.

			"accounts": {
  "emulator-account": {
    "address": "f8d6e0586b0a20c7",
    "key": "5112883de06b9576af62b9aafa7ead685fb7fb46c495039b1a83649d61bff97c"
  "testnet-account": {
    "address": "YOUR GENERATED ADDRESS",
    "key": {
      "type": "hex",
      "index": 0,
      "signatureAlgorithm": "ECDSA_P256",
      "hashAlgorithm": "SHA3_256",
      "privateKey": "YOUR PRIVATE KEY"
"deployments": {
  "emulator": {
    "emulator-account": [
  "testnet": {
    "testnet-account": [

πŸš€ Deploy your HelloWorld smart contract:

			flow project deploy --network=testnet
deploy contract to testnet

Lastly, configure your .env file to point to Flow TestNet so we can interact with your new contract.

In your .env file, change the following:

  1. NEXT_PUBLIC_CONTRACT_ADDRESS to your generated testnet address
  2. NEXT_PUBLIC_ACCESS_NODE to https://rest-testnet.onflow.org
  3. NEXT_PUBLIC_WALLET to https://fcl-discovery.onflow.org/testnet/authn

You can now terminate all your terminals since we no longer need to run our own local blockchain or wallet. Everything lives on testnet!

Run npm run dev to start your application in a terminal, and have a blast with your DApp!

πŸ“ Make Edits!

πŸ” You can also check out your smart contract HelloWorld.cdc in flow/cadence/HelloWorld.cdc.

πŸ’Ό Take a quick look at how your contract get deployed in flow.json.

πŸ“ If you want to make frontend edits, open index.js in pages/index.js.

βš”οΈ Side Quests

πŸƒ Head to your next challenge here.

πŸ’¬ Meet other builders working on this challenge and get help in the πŸ’Ž Emerald City Discord!

πŸ‘‰ Problems, questions, comments on the stack? Post them to the πŸ’Ž Emerald City Discord.