Ethereum Swift API with support for smart contracts, ENS & ERC20

What's New



🌱 New:

🐛 Fixes:

  • [FIX] Cache number representation in EthereumAddress by @DarthMike in #325

⚠️ Changes:

Full Changelog: 1.5.1...1.6.0

web3.swift: Ethereum API for Swift



Swift Package Manager

Use Xcode to add to the project (File -> Swift Packages) or add this to your Package.swift file:

.package(url: "https://github.com/argentlabs/web3.swift", from: "1.1.0")


Add web3.swift to your Podfile:

pod 'web3.swift'

Then run the following command:

$ pod install


Getting Started

Create an instance of EthereumAccount with a EthereumKeyStorage provider. This provides a wrapper around your key for web3.swift to use. NOTE We recommend you implement your own KeyStorage provider, instead of relying on the provided EthereumKeyLocalStorage class. This is provided as an example for conformity to the EthereumSingleKeyStorageProtocol.

import web3

// This is just an example. EthereumKeyLocalStorage should not be used in production code
let keyStorage = EthereumKeyLocalStorage()
let account = try? EthereumAccount.create(replacing: keyStorage, keystorePassword: "MY_PASSWORD")

Create an instance of EthereumHttpClient or EthereumWebSocketClient. This will then provide you access to a set of functions for interacting with the Blockchain.


guard let clientUrl = URL(string: "https://an-infura-or-similar-url.com/123") else { return }
let client = EthereumHttpClient(url: clientUrl)



guard let clientUrl = URL(string: "wss://goerli.infura.io/ws/v3//123") else { return }
let client = EthereumWebSocketClient(url: clientUrl)

You can then interact with the client methods, such as to get the current gas price:

client.eth_gasPrice { (error, currentPrice) in
    print("The current gas price is \(currentPrice)")

If using async/await you can await on the result

let gasPrice = try await client.eth_gasPrice()

Smart contracts: Static types

Given a smart contract function ABI like ERC20 transfer:

function transfer(address recipient, uint256 amount) public returns (bool)

then you can define an ABIFunction with corresponding encodable Swift types like so:

public struct Transfer: ABIFunction {
    public static let name = "transfer"
    public let gasPrice: BigUInt? = nil
    public let gasLimit: BigUInt? = nil
    public var contract: EthereumAddress
    public let from: EthereumAddress?

    public let to: EthereumAddress
    public let value: BigUInt

    public init(contract: EthereumAddress,
                from: EthereumAddress? = nil,
                to: EthereumAddress,
                value: BigUInt) {
        self.contract = contract
        self.from = from
        self.to = to
        self.value = value

    public func encode(to encoder: ABIFunctionEncoder) throws {
        try encoder.encode(to)
        try encoder.encode(value)

This function can be used to generate contract call transactions to send with the client:

let function = transfer(contract: "0xtokenaddress", from: "0xfrom", to: "0xto", value: 100)
let transaction = try function.transaction()

client.eth_sendRawTransaction(transaction, withAccount: account) { (error, txHash) in
    print("TX Hash: \(txHash)")

If using async/await you can await on the result

let txHash = try await client.eth_sendRawTransaction(transaction, withAccount: account)

Generating ABI from a smart contract ABI file

Currently we don't support code generation as making it properly is a bigger project, and should possibly live outside of this repository.

You can try this project instead: imanrep/swiftabigen

Data types

The library provides some types and helpers to make interacting with web3 and Ethereum easier.

  • EthereumAddress: For representation of addresses, including checksum support.
  • BigInt and BigUInt: Using BigInt library
  • EthereumBlock: Represents the block, either number of RPC-specific definitions like 'Earliest' or 'Latest'
  • EthereumTransaction: Wraps a transaction. Encoders and decoders can work with it to generate proper data fields.

Conversion from and to Foundation types

All extensions are namespaced under ''.web3. So for example, to convert an Int to a hex string:

let gwei = 100
let hexgwei = gwei.web3.hexString

Supported conversions:

  • Convert from hex byte string ("0xabc") to Data
  • Convert from hex byte string ("0xabc") to Int
  • Convert from hex byte string ("0xabc") to BigUInt
  • Convert String, Int, BigUInt, Data to a hex byte string ("0xabc")
  • Add or remove hex prefixes when working with String


We support querying ERC20 token data via the ERC20 struct. Calls allow to:

  • Get the token symbol, name, and decimals
  • Get a token balance
  • Retrieve Transfer events


We support querying ERC721 token data via the ERC721 struct. Including:

  • Get the token symbol, name, and decimals
  • Get a token balance
  • Retrieve Transfer events
  • Decode standard JSON for NFT metadata. Please be aware some smart contracts are not 100% compliant with standard.

ZKSync Era

We also include additional helpers to interact with ZKSync Era, by importing web3_zksync.

Take a look at ZKSyncTransaction or use directly ZKSyncClient which has similar API as the EthereumClient

Running Tests

Some of the tests require a private key, which is not stored in the repository. You can ignore these while testing locally, as CI will use the encrypted secret key from Github.

It's better to run only the tests you need, instead of the whole test suite while developing. If you ever need to set up the key locally, take a look at TestConfig.swift where you can manually set it up. Alternatively you can set it up by calling the script setupKey.sh and passing the value (adding 0x) so it's written to an ignored file.


We built web3.swift to be as lightweight as possible. However, given the cryptographic nature of Ethereum, there's a couple of reliable C libraries you will find packaged with this framework:

  • keccac-tiny: An implementation of the FIPS-202-defined SHA-3 and SHAKE functions in 120 cloc (156 lines).
  • Tiny AES: A small and portable implementation of the AES ECB, CTR and CBC encryption algorithms.
  • secp256k1.swift

Package dependencies:

Also for Linux build, we can't use Apple crypto APIs, so we embedded a small subset of CryptoSwift (instead of importing the whole library). Credit to Marcin Krzyżanowski


The initial project was crafted by the team at Argent. However, we encourage anyone to help implement new features and to keep this library up-to-date. For features and fixes, simply submit a pull request to the develop branch. Please follow the contributing guidelines.

For bug reports and feature requests, please open an issue.


Released under the MIT license.


  • Swift Tools 5.3.0
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Last updated: Fri Dec 01 2023 03:26:44 GMT-1000 (Hawaii-Aleutian Standard Time)