Open source skills for Claude Code -- reusable knowledge, algorithms, and reference data packaged as markdown files.

Claude Code skills are markdown files that live in .claude/skills/ in your project. They load on-demand when the topic is relevant, or manually via /skill-name. Unlike CLAUDE.md (loaded every session), skills only consume context when needed.

Each skill has a YAML front matter header:

---
name: device-geometry
description: iPhone/iPad screen geometry and squircle math for layout
---

Followed by the reference content, algorithms, worked examples, and implementation guidance.

iPhone and iPad screen dimensions, corner radii, safe area insets, notch and Dynamic Island measurements for every Face ID iPhone model. Includes the exact superellipse (n=5) formula for computing squircle corner intrusion at any screen coordinate, with verified worked examples and a pixel bitmask generation algorithm.

Eliminates guesswork when positioning UI elements near camera cutouts and rounded screen edges.

Apple Human Interface Guidelines reference covering typography (Dynamic Type sizes, SF Pro text styles, the complete size table from xSmall to AX5), color system (semantic and system colors for light/dark mode), layout (8pt grid, spacing tokens, margins, component heights, safe areas), UI components (bars, buttons, sheets, alerts with SwiftUI mappings), navigation patterns (hierarchical, flat, modal), accessibility checklist (Dynamic Type, VoiceOver, contrast ratios, Reduce Motion), app icon requirements, platform differences (iPhone vs iPad vs Mac), and the Liquid Glass design system introduced in iOS 26.

Includes a "what NOT to do" section with the 12 most common HIG violations.

Complete recipe for creating a new iOS/Mac Catalyst app from scratch using XcodeGen. Covers project.yml configuration, Config.xcconfig with optional Local.xcconfig for code signing, asset catalog setup, app icon generation (RGB, no alpha), Info.plist keys needed for App Store validation, and the full setup sequence from mkdir to gh repo create.

Handles the private-vs-public repo decision (team ID in project.yml vs gitignored Local.xcconfig) and includes a "what NOT to do" section covering the alpha channel, missing icon keys, and export compliance pitfalls.

Companion scripts that implement skill algorithms.

Generates iOS + Mac Catalyst app icons at all required sizes (16px through 1024px). Always outputs RGB with no alpha channel. Supports built-in shapes (paw print, circle, text) or use as a starting point for custom icons.

pip3 install Pillow
python3 tools/generate_ios_icon.py --bg '#E8683A' --shape paw output_dir/
python3 tools/generate_ios_icon.py --bg '#2A9D8F' --shape text --text 'AB' output_dir/
python3 tools/generate_ios_icon.py --bg '30,120,200' --shape none output_dir/

Overlays a device screen mask on a simulator screenshot. Renders squircle corners, Dynamic Island / notch cutout, and optional safe area boundary lines. Auto-detects device from pixel dimensions.

pip3 install Pillow numpy
python3 tools/apply_device_mask.py screenshot.png              # basic mask
python3 tools/apply_device_mask.py --safe-areas screenshot.png # + safe area lines
python3 tools/apply_device_mask.py --device iphone16pro screenshot.png

Copy a skill file into your project:

mkdir -p .claude/skills
cp skills/device-geometry.md .claude/skills/

Or symlink to keep it updated:

mkdir -p .claude/skills
ln -s /path/to/claude-skills/skills/device-geometry.md .claude/skills/

PRs welcome. A good skill:

• Solves a problem that causes repeated trial-and-error across sessions
• Contains precise, unambiguous algorithms (not vague guidance)
• Includes worked examples that serve as correctness checks
• Lists common mistakes in a "what NOT to do" section
• References authoritative sources

Other repos in this collection:

• iospharo — Pharo Smalltalk VM for iOS and Mac Catalyst (interpreter-only, low-bit oop encoding for ASLR compatibility).
• pharo-headless-test — Headless Pharo test runner with a fake GUI; clicks menus, takes screenshots, runs SUnit without a display.
• soogle — Smalltalk code search engine that indexes packages across Pharo, Squeak, GemStone and more.
• validate_smalltalk_image — Standalone validator and export tool for Spur-format Smalltalk image files (heap integrity, SHA-256 manifests, reference graphs).

GPLv3 -- see LICENSE file.