web3.swift

Web3.swift is the Swift library that handles that. It's the Swift equivalent of web3.js or ethers.js.

MIT license. Provides typed Ethereum JSON-RPC calls, ABI encoding/decoding, contract interaction, and transaction signing from native Swift code. Works with any Ethereum node or provider (Infura, Alchemy, etc.).

Fully free. Client library. Install via Swift Package Manager and use. No hosting, no paid tier.

The catch: this library is effectively in maintenance mode with no recent activity. The Ethereum ecosystem moves fast (new EIPs, new standards, chain upgrades), and a dormant library risks falling behind. Check the last commit date before depending on this for production. If you need active development and broader chain support, consider using ethers.js via a JavaScript bridge or look at alternative Swift Ethereum libraries. The Swift blockchain development community is small, and your options are limited.