Developer Quickstart

This guide will walk developers through writing a smart contract in Sway, a simple test, deploying to Fuel, and building a frontend.

Before we begin, it may be helpful to understand the terminology that will be used throughout the docs and how they relate to each other:

  • Fuel: the Fuel blockchain.
  • FuelVM: the virtual machine powering Fuel.
  • Sway: the domain-specific language crafted for the FuelVM; it is inspired by Rust.
  • Forc: the build system and package manager for Sway, similar to Cargo for Rust.

Understand Sway Program Types

There are four types of Sway programs:

  • contract
  • predicate
  • script
  • library

Contracts provide long-lived artifacts on the blockchain, while scripts will just exist for the duration of the transaction, and a library is simply a project designed for code reuse and is not directly deployable. Predicates are like scripts which return a boolean value to indicate ownership of an asset, however, they cannot access state.

The main features of a smart contract that differentiate it from scripts or predicates are that it is callable and stateful.

A script is runnable bytecode on the chain which can call contracts to perform some task. It does not represent ownership of any resources and it cannot be called by a contract.

deployable on the blockchain:can have state:can access state:callable on the blockchain:designed for code reuse:
(via a contract or predicate)

See the chapter on program types for more information.


Start by installing the Rust toolchain.

Then, install the Fuel toolchain.

Make sure you have the latest version of fuelup by running the following command:

$ fuelup self update
Fetching binary from
Downloading component fuelup without verifying checksum
Unpacking and moving fuelup to /var/folders/tp/0l8zdx9j4s9_n609ykwxl0qw0000gn/T/.tmpiNJQHt
Moving /var/folders/tp/0l8zdx9j4s9_n609ykwxl0qw0000gn/T/.tmpiNJQHt/fuelup to /Users/.fuelup/bin/fuelup

Then run fuelup toolchain install beta-2 to install the beta-2 toolchain.

Finally, set the beta-2 toolchain as your default distribution with the following command:

$ fuelup default beta-2
default toolchain set to 'beta-2-aarch64-apple-darwin'

You can check your current toolchain anytime by running fuelup show.

Having problems with this part? Post your question on our forum To help you as efficiently as possible, include the output of this command in your post: fuelup show.

Your First Sway Project

We'll build a simple counter contract with two functions: one to increment the counter, and one to return the value of the counter.

A few pieces of info that will be helpful before moving on:

  • This guide was created using VSCode as the code editor.
  • Download the Sway language extension in VSCode to get syntax highlighting, keyboard shortcuts, and more.
  • Download the rust-analyzer extension in VSCode to get syntax highlighting, code completion, and more.

Start by creating a new, empty folder. We'll call it fuel-project.

Writing the Contract

Then with forc installed, create a contract project inside of your fuel-project folder:

$ cd fuel-project
$ forc new counter-contract
To compile, use `forc build`, and to run tests use `forc test`


Read the Docs:
- Sway Book:
- Rust SDK Book:
- TypeScript SDK:

Join the Community:
- Follow us @SwayLang:
- Ask questions in dev-chat on Discord:

Report Bugs:
- Sway Issues:

Here is the project that Forc has initialized:

$ tree counter-contract
├── Forc.toml
└── src
    └── main.sw

Forc.toml is the manifest file (similar to Cargo.toml for Cargo or package.json for Node) and defines project metadata such as the project name and dependencies.

Open your project in a code editor and delete the boilerplate code in src/main.sw so that you start with an empty file.

Every Sway file must start with a declaration of what type of program the file contains; here, we've declared that this file is a contract.


Next, we'll define a storage value. In our case, we have a single counter that we'll call counter of type 64-bit unsigned integer and initialize it to 0.

storage {
    counter: u64 = 0,


An ABI defines an interface, and there is no function body in the ABI. A contract must either define or import an ABI declaration and implement it. It is considered best practice to define your ABI in a separate library and import it into your contract because this allows callers of the contract to import and use the ABI in scripts to call your contract.

For simplicity, we will define the ABI directly in the contract file.

abi Counter {
    #[storage(read, write)]
    fn increment();

    fn count() -> u64;

Going line by line

#[storage(read, write)] is an annotation which denotes that this function has permission to read and write values in storage.

fn increment(); - We're introducing the functionality to increment and denoting it shouldn't return any value.

#[storage(read)] is an annotation which denotes that this function has permission to read values in storage.

fn counter() -> u64; - We're introducing the functionality to increment the counter and denoting the function's return value.

Implement ABI

Below your ABI definition, you will write the implementation of the functions defined in your ABI.

impl Counter for Contract {
    fn count() -> u64 {

    #[storage(read, write)]
    fn increment() {
        storage.counter = storage.counter + 1;

Note:return storage.counter; is equivalent to storage.counter.

What we just did

In fn count(), we read and return the variable counter from storage.

    fn count() -> u64 {

In fn increment(), we read the variable counter from storage and increment its value by one. We then store the new value back in counter.

    fn increment() {
        storage.counter = storage.counter + 1;

Here's what your code should look like so far:

File: ./counter-contract/src/main.sw


storage {
    counter: u64 = 0,

abi Counter {
    #[storage(read, write)]
    fn increment();

    fn count() -> u64;

impl Counter for Contract {
    fn count() -> u64 {

    #[storage(read, write)]
    fn increment() {
        storage.counter = storage.counter + 1;

Build the Contract

From inside the fuel-project/counter-contract directory, run the following command to build your contract:

$ forc build
  Compiled library "core".
  Compiled library "std".
  Compiled contract "counter-contract".
  Bytecode size is 232 bytes.

Let's have a look at the content of the counter-contract folder after building:

$ tree .
├── Forc.lock
├── Forc.toml
├── out
│   └── debug
│       ├── counter-contract-abi.json
│       ├── counter-contract-contract-id
│       ├── counter-contract-storage_slots.json
│       └── counter-contract.bin
└── src
    └── main.sw

We now have an out directory that contains our build artifacts such as the JSON representation of our ABI and the contract bytecode.

Testing your Contract

We will start by adding a Rust integration test harness using a Cargo generate template. If this is your first time going through this quickstart, you'll need to install the cargo generate command. In the future, you can skip this step as it will already be installed.

Navigate to your contract and then run the installation command:

$ cd counter-contract
changed directory into `counter-countract`
$ cargo install cargo-generate
 Updating index...
 installed package `cargo-generate v0.17.3`

Note: You can learn more about cargo generate by visiting its repository.

Now, let's generate the default test harness with the following:

$ cargo generate --init fuellabs/sway templates/sway-test-rs --name counter-contract
⚠️   Favorite `fuellabs/sway` not found in config, using it as a git repository:
🤷   Project Name : counter-contract
🔧   Destination: /home/user/path/to/counter-contract ...
🔧   Generating template ...
[1/3]   Done: Cargo.toml
[2/3]   Done: tests/
[3/3]   Done: tests
🔧   Moving generated files into: `/home/user/path/to/counter-contract`...
✨   Done! New project created /home/user/path/to/counter-contract

Let's have a look at the result:

$ tree .
├── Cargo.toml
├── Forc.lock
├── Forc.toml
├── out
│   └── debug
│       ├── counter-contract-abi.json
│       ├── counter-contract-contract-id
│       ├── counter-contract-storage_slots.json
│       └── counter-contract.bin
├── src
│   └── main.sw
└── tests

We have two new files!

  • The Cargo.toml is the manifest for our new test harness and specifies the required dependencies including fuels the Fuel Rust SDK.
  • The tests/ contains some boilerplate test code to get us started, though doesn't call any contract methods just yet.

Now that we have our default test harness, let's add some useful tests to it.

At the bottom of test/, define the body of can_get_contract_id(). Here is what your code should look like to verify that the value of the counter did get incremented:

File: tests/

async fn can_get_contract_id() {
    let (instance, _id) = get_contract_instance().await;

    // Increment the counter
    let _result = instance.methods().increment().call().await.unwrap();

    // Get the current value of the counter
    let result = instance.methods().count().call().await.unwrap();

    // Check that the current value of the counter is 1.
    // Recall that the initial value of the counter was 0.
    assert_eq!(result.value, 1);

Run cargo test in the terminal. If all goes well, the output should look as follows:

$ cargo test
  running 1 test
  test can_get_contract_id ... ok
  test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.11s

Deploy the Contract

It's now time to deploy the contract to the testnet. We will show how to do this using forc from the command line, but you can also do it using the Rust SDK or the TypeScript SDK.

In order to deploy a contract, you need to have a wallet to sign the transaction and coins to pay for gas. First, we'll create a wallet.

Install the Wallet CLI

Follow these steps to set up a wallet and create an account.

After typing in a password, be sure to save the mnemonic phrase that is output.

With this, you'll get a fuel address that looks something like this: fuel1efz7lf36w9da9jekqzyuzqsfrqrlzwtt3j3clvemm6eru8fe9nvqj5kar8. Save this address as you'll need it to sign transactions when we deploy the contract.

Get Testnet Coins

With your account address in hand, head to the testnet faucet to get some coins sent to your wallet.

Deploy To Testnet

Now that you have a wallet, you can deploy with forc deploy and passing in the testnet endpoint like this:

forc deploy --url --gas-price 1

Note: We set the gas price to 1. Without this flag, the gas price is 0 by default and the transaction will fail.

The terminal will ask for the address of the wallet you want to sign this transaction with, paste in the address you saved earlier, it looks like this: fuel1efz7lf36w9da9jekqzyuzqsfrqrlzwtt3j3clvemm6eru8fe9nvqj5kar8

The terminal will output your Contract id like this:

Contract id: 0xe5dc89f7b8c62e40927a6b17f144583bf6571d2468ab1e2554d2731f4c9fc428

Be sure to save this as you will need it to build a frontend with the Typescript SDK later in this tutorial.

The terminal will output a message to sign and prompt you for a signature. Open a new terminal tab and view your accounts by running forc wallet list. If you followed these steps, you'll notice you only have one account, 0.

Grab the message to sign from your other terminal and sign with your account by running the following command:

forc wallet sign` + `[message to sign, without brackets]` + `[the account number, without brackets]`

Your command should look like this:

$ forc wallet sign 16d7a8f9d15cfba1bd000d3f99cd4077dfa1fce2a6de83887afc3f739d6c84df 0
Please enter your password to decrypt initialized wallet's phrases:
Signature: 736dec3e92711da9f52bed7ad4e51e3ec1c9390f4b05caf10743229295ffd5c1c08a4ca477afa85909173af3feeda7c607af5109ef6eb72b6b40b3484db2332c

Enter your password when prompted, and you'll get back a signature. Save that signature, and return to your other terminal window, and paste that in where its prompting you to provide a signature for this transaction.

Finally, you will get back a TransactionId to confirm your contract was deployed. With this ID, you can head to the block explorer and view your contract.

Note You should prefix your TransactionId with 0x to view it in the block explorer

block explorer

Create a Frontend to Interact with Contract

Now we are going to

  1. Initialize a React project.
  2. Install the fuels SDK dependencies.
  3. Modify the App.
  4. Run our project.

Initialize a React project

To split better our project let's create a new folder frontend and initialize our project inside it.

In the terminal, go back up one directory and initialize a react project using Create React App.

$ cd ..
$ npx create-react-app frontend --template typescript
Success! Created frontend at Fuel/fuel-project/frontend

You should now have your outer folder, fuel-project, with two folders inside: counter-contract and frontend

project folder structure

Install the fuels SDK dependency

The fuels umbrella package includes all the main tools you need for your frontend; Wallet, Contracts, Providers, and more.

Also, it contains the routines for ABI TypeScript generation.

ABI stands for Application Binary Interface. ABI's inform the application the interface to interact with the VM, in other words, they provide info to the APP such as what methods a contract has, what params, types it expects, etc...


Move into the frontend folder, then run:

$ cd frontend
$ npm install fuels@0.29.1 --save
added 114 packages, and audited 115 packages in 29s
Generating contract types

To make it easier to interact with our contract we use fuels typegen command to interpret the output ABI JSON from our contract, and generate Typescript definitions based on it. This JSON was created when we executed the forc build command to compile our Sway Contract into binary.

If you see the folder fuel-project/counter-contract/out you will be able to see the ABI JSON there. If you want to learn more, read the ABI spec.

Inside the fuel-project/frontend directory run:

$ npx fuels typegen -i ../counter-contract/out/debug/*-abi.json -o ./src/contracts
Generating files..

 - src/contracts/CounterContractAbi.d.ts
 - src/contracts/factories/CounterContractAbi__factory.ts
 - src/contracts/index.ts


Now you should be able to find a new folder fuel-project/frontend/src/contracts. This folder was auto-generated by our fuels typegen command, and these files abstract the work we would need to do to create a contract instance, and generate a complete TypeScript interface to the Contract, making easy to develop.

Create A Wallet (Again)

For interacting with the fuel network we have to submit signed transactions with enough funds to cover network fees. The Fuel TS SDK don't currently support Wallet integrations, requiring us to have a non-safe wallet inside the WebApp using a privateKey.

Note: This should be done only for development purpose. Never expose a web app with a private key inside. The Fuel Wallet is in active development, follow the progress here.

In the root of the frontend project create a file named createWallet.js and add the following code:

File: ./frontend/createWallet.js

const { Wallet } = require("fuels");

const wallet = Wallet.generate();

console.log("address", wallet.address.toString());
console.log("private key", wallet.privateKey);

In a terminal, run the following command:

$ node createWallet.js
address fuel160ek8t7fzz89wzl595yz0rjrgj3xezjp6pujxzt2chn70jrdylus5apcuq
private key 0x719fb4da652f2bd4ad25ce04f4c2e491926605b40e5475a80551be68d57e0fcb

Note: You should use the generated address and private key.

Save the private key, you will need this later to set it as a string value for a variable WALLET_SECRET in your App.tsx file. More on that below.

First, take the address of your wallet and use it to get some coins from the testnet faucet.

Now you're ready to build and ship ⛽

Note: The team is working to simplify the process of creating a wallet, and eliminate the need to create a wallet twice. Keep an eye out for these updates.

Modify the App

Inside the frontend/src folder let's add code that interacts with our contract. Read the comments to help you understand the App parts. Change the file fuel-project/frontend/src/App.tsx to:

File: ./frontend/src/App.tsx

import React, { useEffect, useState } from "react";
import { Wallet } from "fuels";
import "./App.css";
// Import the contract factory -- you can find the name in index.ts.
// You can also do command + space and the compiler will suggest the correct name.
import { CounterContractAbi__factory } from "./contracts";

// The address of the contract deployed the Fuel testnet

//the private key from createWallet.js

// Create a Wallet from given secretKey in this case
// The one we configured at the chainConfig.json
const wallet = Wallet.fromPrivateKey(

// Connects out Contract instance to the deployed contract
// address using the given wallet.
const contract = CounterContractAbi__factory.connect(CONTRACT_ID, wallet);

function App() {
  const [counter, setCounter] = useState(0);
  const [loading, setLoading] = useState(false);

  useEffect(() => {
    async function main() {
      // Executes the counter function to query the current contract state
      // the `.get()` is read-only, because of this it don't expand coins.
      const { value } = await contract.functions.count().get();
  }, []);

  async function increment() {
    // a loading state
    // Creates a transactions to call the increment function
    // because it creates a TX and updates the contract state this requires the wallet to have enough coins to cover the costs and also to sign the Transaction
    try {
      await contract.functions.increment().txParams({ gasPrice: 1 }).call();
      const { value } = await contract.functions.count().get();
    } finally {
  return (
    <div className="App">
      <header className="App-header">
        <p>Counter: {counter}</p>
        <button disabled={loading} onClick={increment}>
          {loading ? "Incrementing..." : "Increment"}
export default App;

Run your project

Now it's time to have fun, run the project in your browser.

Inside the fuel-project/frontend directory run:

$ npm start
Compiled successfully!

You can now view frontend in the browser.

  Local:            http://localhost:3001
  On Your Network:

Note that the development build is not optimized.
To create a production build, use npm run build.

screenshot of the UI

✨⛽✨ Congrats you have completed your first DApp on Fuel ✨⛽✨

Here is the repo for this project. If you run into any problems, a good first step is to compare your code to this repo and resolve any differences.

Tweet us @fuellabs_ letting us know you just built a dapp on Fuel, you might get invited to a private group of builders, be invited to the next Fuel dinner, get alpha on the project, or something 👀.

Updating The Contract

If you make changes to your contract, here are the steps you should take to get your frontend and contract back in sync:

  • In your contract directory, run forc build

  • In your contract directory, redeploy the contract by running this command and following the same steps as above to sign the transaction with your wallet: forc deploy --url --gas-price 1

  • In your frontend directory, re-run this command: npx fuels typegen -i ../counter-contract/out/debug/*-abi.json -o ./src/contracts

  • In your fuel-project/frontend directory, update the contract ID in your App.tsx file

Need Help?

Get help from the team by posting your question in the Fuel Forum.