Token efficiency
Your agent skips millions of tokens of reasoning and reads guidance only for the issues flagged.
Code review expertise for your coding agents.
SwiftFairy
A macOS app to help your agents with Apple's APIs
SwiftFairy checks your agent's code entirely on your Mac, returning focused findings to your agent with explanations, guidance, and code examples.
Review your Swift and SwiftUI code to improve its correctness, performance, and maintainability.
Activate your free trial within the app at any time.
Why your agent works better with SwiftFairy
Cross-file insight
Follows your view hierarchy across files and presentations, beyond single views and functions.
Deep knowledge
Built on our books and articles, and Natalia's work on Apple's SwiftUI team.
What knowledge SwiftFairy brings to your agent
SwiftFairy organises its knowledge into Scrolls. Each Scroll covers a related set of APIs or a development domain, combining best-practice guidance, known issue patterns, and code examples. Together, the Scrolls flag over 350 issues in your code.
Proper SwiftUI
Correct subtle bugs and performance issues in data flow, state ownership, and view updates by using SwiftUI as it was designed to be used.
SwiftUI Layout & Resizability
Build interfaces that adapt to any window size, device, and text size by sizing views flexibly, structuring scrolling content correctly, and choosing the right SwiftUI layout API for each job.
Performant Swift Charts
Improve rendering and interaction performance by structuring charts and surrounding views to limit unnecessary updates and use Swift Charts APIs effectively.
Modern Swift
Refine code for clarity, maintainability, and performance through idiomatic use of modern Swift APIs, including modern Swift concurrency and collection processing.
How SwiftFairy reviews your code
You ask your agent to review your code with SwiftFairy.
Review my app with SwiftFairy.
Your agent sends the code
Your agent sends the relevant code and supporting declarations to SwiftFairy.
SwiftFairy analyses your codebase locally on your Mac.
Reviewing your code
SwiftFairy identifies subtle bugs, performance issues, and opportunities to improve API usage, returning guidance and code examples to help your agent address them.
Your agent accepts precise, scoped guidance for detected issues.
Review finding
Explanation + guidance
{ } Code exampleYour agent adapts the guidance
Your agent uses the findings and their accompanying code examples to resolve issues in your code.
Who's behind SwiftFairy?
We're the developers behind Nil Coalescing, where we build apps and share our knowledge of Swift, SwiftUI, and Swift Charts through books, articles, and talks. SwiftFairy brings together our experience in app development and teaching, including Natalia's work designing and developing APIs on Apple's core SwiftUI team.
Many readers have asked us to turn the knowledge in our books and articles into skills for coding agents. We tried. Giving an agent all of that guidance up front can swamp its context. Splitting it into nested skill files creates another problem: the agent may miss the instruction to open a relevant file or fail to look up supporting details when it needs them. Either way, important guidance can be missed.
SwiftFairy keeps the knowledge from our books and articles outside your agent's context until it is relevant. It analyses the code, identifies potential issues, and returns focused guidance with accompanying examples. Your agent spends fewer tokens processing background material and has the information it needs to act.
How to access SwiftFairy's knowledge
Individual knowledge Scrolls and bundles are available as a lifetime purchase, a fixed term, or a subscription.
Lifetime
Lifetime access to the Scroll, including all future updates.
Fixed term
Access for a set period, without automatic renewal:7, 30, or 365 days.
Subscription
Access renews automatically each week, month, or year until cancelled.
Download SwiftFairy for macOS
Version 2026.10.2. Paged whole-project audits, faster evaluation and the SwiftUI Layout & Resizability scroll.
Requires macOS 26.0 or later and an Apple silicon Mac.