SwiftLint

What it is

SwiftLint enforces Swift style and conventions, with hundreds of configurable rules, autocorrection and custom rule support.

Configure rules in .swiftlint.yml and run as a build phase or in CI. Analyzer rules use full type information and run separately.

Installation

brew install swiftlint

Getting started

The smallest useful thing you can do with it, and what each part means.

Configuration

123456789101112131415161718192021222324disabled_rules:
  - trailing_whitespace

opt_in_rules:
  - force_unwrapping        # flags every !
  - empty_count
  - first_where
  - explicit_init
  - implicitly_unwrapped_optional

excluded:
  - .build
  - Generated

line_length:
  warning: 120
  error: 200
  ignores_urls: true

custom_rules:
  no_print:
    regex: '\bprint\('
    message: "Use the logger, not print."
    severity: warning

force_unwrapping is opt-in but is the highest-value rule in Swift — every ! is a potential crash, and flagging them makes the risk visible in review.

Advanced usage

Where the library earns its place over a simpler alternative.

Build integration and analyzer rules

bash

123456789101112# Xcode build phase — warn without failing the build locally
if which swiftlint > /dev/null; then
  swiftlint --quiet
else
  echo "warning: SwiftLint not installed"
fi

# CI: fail on any violation
swiftlint --strict

# Analyzer rules need a compiler log — they use type information
swiftlint analyze --compiler-log-path build.log

Analyzer rules such as unused_import require the compile log because they need type resolution — they are unavailable in a plain lint run.

Errors and fixes

The failures you are most likely to hit, and what actually resolves them.

Violations in generated code: Add the directory to `excluded`. SwiftLint lints everything under the config root by default.
Analyzer rules report nothing: They require swiftlint analyze with a compiler log path.

Best practices

Enable force_unwrapping and force_try; they surface the crash-prone lines.
Run --strict in CI but not locally, so development is not blocked by warnings.
Exclude generated code and .build, or every run drowns in irrelevant violations.
Always give a reason when suppressing a rule inline.

Background

Why it exists, and what it was reacting to.

From Realm, SwiftLint became the community standard for keeping Swift codebases consistent, and catches a number of correctness issues alongside pure style.

Related libraries

Others in Testing for Swift.

SnapshotTesting

Quick & Nimble