SwiftFormat — Opinionated Swift Code Formatter

Introduction

SwiftFormat is an opinionated code formatter for Swift that enforces a consistent style across your codebase. It rewrites Swift files in place based on a comprehensive set of configurable rules covering indentation, spacing, brace placement, import sorting, and dozens of other style preferences.

What SwiftFormat Does

• Automatically reformats Swift source files to match configured style rules
• Provides 70+ individual formatting rules that can be enabled or disabled
• Runs as a CLI tool, Xcode source editor extension, or SPM build plugin
• Supports a .swiftformat configuration file for project-wide settings
• Integrates with Git hooks and CI pipelines for automated enforcement

Architecture Overview

SwiftFormat parses Swift source into a token stream using its own lightweight tokenizer (not the full Swift compiler). It then applies a sequence of formatting rules as token-level transformations. Each rule is an independent function that scans and modifies the token array. Rules are applied in a defined order, with multiple passes to resolve dependencies between rules. The formatted token stream is then serialized back to source text.

Self-Hosting & Configuration

• Install via Homebrew: brew install swiftformat
• Or via Mint, CocoaPods, or as an SPM package plugin
• Create a .swiftformat file to configure rules, indentation, and excluded paths
• Add as a Git pre-commit hook for automatic formatting on commit
• Install the Xcode Source Editor Extension for in-editor formatting

Key Features

• Token-based formatting that preserves comments and non-standard syntax
• Configurable indentation (tabs or spaces with custom width)
• Import sorting, redundant keyword removal, and trailing comma insertion
• Xcode extension for formatting selections or entire files within the editor
• Lint mode (--lint) that reports violations without modifying files for CI use

Comparison with Similar Tools

• swift-format (Apple) — Apple's official formatter; fewer rules and less configurable
• SwiftLint — focuses on linting and warnings rather than auto-formatting; complementary tool
• Prettier — multi-language formatter; does not support Swift
• clang-format — C/C++/Objective-C formatter; no Swift support
• Xcode auto-indentation — basic indentation only; no comprehensive style enforcement

FAQ

Q: What is the difference between SwiftFormat and SwiftLint? A: SwiftFormat rewrites code to match style rules. SwiftLint reports violations and can auto-correct some issues. Many teams use both together.

Q: Can I disable specific rules for parts of my code? A: Yes. Use // swiftformat:disable <rule> and // swiftformat:enable <rule> comments to toggle rules inline.

Q: Does SwiftFormat support Swift 6 and strict concurrency? A: Yes. The tokenizer handles modern Swift syntax including actors, async/await, and parameter packs.

Q: Will SwiftFormat change the behavior of my code? A: The formatter only changes whitespace, formatting, and certain redundant syntax. It does not alter logic or semantics. The --dryrun flag lets you preview all changes before applying.

Sources

• https://github.com/nicklockwood/SwiftFormat
• https://github.com/nicklockwood/SwiftFormat/blob/main/Rules.md