Writes and reviews Swift FormatStyle code, replacing legacy Formatter subclasses and C-style String(format:) with modern .formatted() APIs. Use when formatting numbers, dates, durations, measurements, lists, names, byte counts, or URLs.

Write and review Swift code that formats values for display, ensuring modern FormatStyle APIs are used instead of legacy Formatter subclasses or C style formatting. Review process: 1. Check for legacy formatting patterns and replace with modern FormatStyle equivalents using references/anti patterns.md . 1. Validate number, percent, and currency formatting using references/numeric styles.md . 1. Validate date and time formatting using references/date styles.md . 1. Validate duration formatting using references/duration styles.md . 1. Validate measurement, list, person name, byte count, and URL formatting using references/other styles.md . 1. Check SwiftUI Text views for proper FormatStyle integration using references/swiftui.md . If doing partial work, load only the relevant reference files. Core Instructions Target iOS 15+ / macOS 12+ minimum for basic FormatStyle. Duration and URL styles require iOS 16+ / macOS 13+. Never use legacy Formatter subclasses ( DateFormatter , NumberFormatter , MeasurementFormatter , DateComponentsFormatter , DateIntervalFormatter , PersonNameComponentsFormatter , ByteCountFormatter ). Never use C style String(format:) for number formatting. Always use .formatted() or FormatStyle directly. Never use DispatchQueue for formatting on background threads FormatStyle types are value types and thread safe. Prefer .formatted() instance method for simple cases, and explicit FormatStyle types for reusable or complex configurations. In SwiftUI, use Text( :format:) instead of Text("\(value.formatted())") . Use Decimal instead of Float / Double for currency values. FormatStyle types are locale aware by default. Only set locale explicitly when you need a specific locale different from the user's current locale. FormatStyle types conform to Codable and Hashable , making them safe to store and compare. Output Format If the user asks for a review, organize findings by file. For each issue: 1. State the file and relevant line(s). 2. Name the anti pattern being replaced. 3. Show a brief before/after code fix. Skip files with no issues. End with a prioritized summary of the most impactful changes to make first. If the user asks you to write or fix formatting code, make the changes directly instead of returning a findings report. Example output: RecordingView.swift Line 42: Use Duration.formatted() instead of String(format:) for time display. Line 78: Use Text( :format:) instead of string interpolation. Summary 1. Legacy formatting (high): C style String(format:) on line 42 should use Duration.formatted(). 2. SwiftUI (medium): Text interpolation on line 78 should use the format: parameter directly. End of example. References references/anti patterns.md legacy patterns to replace: String(format:), DateFormatter, NumberFormatter, and other Formatter subclasses. references/numeric styles.md number, percent, and currency formatting with rounding, precision, sign, notation, scale, and grouping. references/date styles.md date/time compositing, ISO 8601, relative, verbatim, HTTP, interval, and components styles. references/duration styles.md Duration.TimeFormatStyle and Duration.UnitsFormatStyle with patterns, units, width, and fractional seconds. references/other styles.md measurement, list, person name, byte count, URL formatting, and custom FormatStyle creation. references/swiftui.md SwiftUI Text integration and best practices.

swift-format-style