# Periphery — Detect Unused Code in Swift Projects

> A static analysis tool that identifies unused classes, functions, protocols, properties, and imports in Swift codebases, helping teams reduce binary size and eliminate dead code with confidence.

## Install

Save as a script file and run:

# Periphery — Detect Unused Code in Swift Projects

## Quick Use
```bash
brew install peripheryapp/periphery/periphery
cd /path/to/your/project
periphery scan --setup
```

## Introduction
Periphery scans Swift projects to find declarations that are never referenced. Unlike simple grep-based tools, it builds the full project with the Swift compiler and analyzes the indexed symbol graph, so its results account for protocol conformances, dynamic dispatch, and cross-module references.

## What Periphery Does
- Identifies unused classes, structs, enums, functions, properties, and type aliases
- Detects unused protocol conformances and protocol declarations with no adopters
- Finds redundant public access control where internal would suffice
- Scans Objective-C bridging headers for unused @objc-exposed declarations
- Reports unused import statements that add compile-time overhead

## Architecture Overview
Periphery invokes xcodebuild or swift build to compile the project and produce a full index store — the same database Xcode uses for jump-to-definition. It then walks the index store's symbol graph to determine which declarations are referenced and which are not. This compiler-backed approach means it understands generics, protocol extensions, and conditional compilation blocks correctly.

## Self-Hosting & Configuration
- Install via Homebrew or download the binary from GitHub releases
- Run periphery scan --setup on first use to select targets and build configuration
- Use a .periphery.yml config file to persist scan settings and exclusion patterns
- Exclude generated code or third-party sources with the --index-exclude flag
- Integrate into CI by running periphery scan and checking the exit code for regressions

## Key Features
- Compiler-accurate analysis via the Swift index store rather than text matching
- Supports Xcode projects, Swift Package Manager, and Bazel build systems
- Incremental scanning that reuses previous build artifacts for faster re-scans
- Configurable severity levels to distinguish warnings from hard errors in CI
- Xcode-compatible output format so results appear as warnings in the IDE

## Comparison with Similar Tools
- **SwiftLint** — enforces style rules; Periphery finds dead code specifically
- **Xcode's built-in warnings** — catches some unused variables; Periphery goes deeper into types and protocols
- **fus** — simpler unused code finder; Periphery uses the compiler index for accuracy
- **Sourcery** — code generation tool; Periphery is the opposite, finding code to remove
- **swift-dependencies** — tracks module-level dependencies; Periphery works at the symbol level

## FAQ
**Q: Does it support Swift Package Manager projects?**
A: Yes. Periphery builds SPM projects with swift build and analyzes the resulting index store.

**Q: Can it produce false positives?**
A: Rarely. It may flag declarations used only via runtime features like @IBAction or Codable synthesis. Use the comment annotation // periphery:ignore to suppress those.

**Q: How long does a scan take?**
A: The initial scan requires a full build, which depends on project size. Subsequent scans with incremental builds typically complete in seconds.

**Q: Does it work with mixed Objective-C and Swift projects?**
A: Yes. It scans Objective-C bridging headers and detects unused @objc-exposed Swift declarations, though pure Objective-C analysis is limited.

## Sources
- https://github.com/peripheryapp/periphery
- https://peripheryapp.com

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Source: https://tokrepo.com/en/workflows/asset-0b919324
Author: Script Depot