Skills

Skills are specialized instruction sets that GSD loads when the task matches. They provide domain-specific guidance for the LLM — coding patterns, framework idioms, testing strategies, and tool usage.

Skills follow the open Agent Skills standard and are not GSD-specific — they work with Claude Code, OpenAI Codex, Cursor, GitHub Copilot, Windsurf, and 40+ other agents.

Skill Directories

GSD reads skills from two locations, in priority order:

Location	Scope	Description
~/.agents/skills/	Global	Shared across all projects and all compatible agents
.agents/skills/ (project root)	Project	Project-specific skills, committable to version control

Global skills take precedence over project skills when names collide.

Migration from ~/.gsd/agent/skills/: On first launch after upgrading, GSD automatically copies skills from the legacy ~/.gsd/agent/skills/ directory to ~/.agents/skills/. The old directory is preserved for backward compatibility.

Installing Skills

Skills are installed via the skills.sh CLI:

# Interactive — choose skills and target agents
npx skills add dpearson2699/swift-ios-skills

# Install specific skills non-interactively
npx skills add dpearson2699/swift-ios-skills --skill swift-concurrency --skill swiftui-patterns -y

# Install all skills from a repo
npx skills add dpearson2699/swift-ios-skills --all

# Check for updates
npx skills check

# Update installed skills
npx skills update

Onboarding Catalog

During gsd init, GSD detects the project’s tech stack and recommends relevant skill packs. For brownfield projects, detection is automatic; for greenfield projects, the user picks a tech stack.

The curated catalog is maintained in src/resources/extensions/gsd/skill-catalog.ts. Each entry maps a tech stack to a skills.sh repo and specific skill names.

Available Skill Packs

Swift (any Swift project — Package.swift or .xcodeproj detected):

• SwiftUI — layout, navigation, animations, gestures, Liquid Glass
• Swift Core — Swift language, concurrency, Codable, Charts, Testing, SwiftData

iOS (only when .xcodeproj targets iphoneos via SDKROOT):

• iOS App Frameworks — App Intents, Widgets, StoreKit, MapKit, Live Activities
• iOS Data Frameworks — CloudKit, HealthKit, MusicKit, WeatherKit, Contacts
• iOS AI & ML — Core ML, Vision, on-device AI, speech recognition
• iOS Engineering — networking, security, accessibility, localization, Instruments
• iOS Hardware — Bluetooth, CoreMotion, NFC, PencilKit, RealityKit
• iOS Platform — CallKit, EnergyKit, HomeKit, SharePlay, PermissionKit

Web:

• React & Web Frontend — React best practices, web design, composition patterns
• React Native — cross-platform mobile patterns
• Frontend Design & UX — frontend design, accessibility

Languages:

• Rust — Rust patterns and best practices
• Python — Python patterns and best practices
• Go — Go patterns and best practices

General:

• Document Handling — PDF, DOCX, XLSX, PPTX creation and manipulation

Maintaining the Catalog

The skill catalog lives in src/resources/extensions/gsd/skill-catalog.ts. To add or update a pack:

1. Add a SkillPack entry to the SKILL_CATALOG array with repo, skills, and matching criteria
2. For language-detection matching, use matchLanguages (values from detection.ts LANGUAGE_MAP)
3. For Xcode platform matching, use matchXcodePlatforms (e.g., ["iphoneos"] — parsed from SDKROOT in project.pbxproj)
4. For file-presence matching, use matchFiles (checked against PROJECT_FILES in detection.ts)
5. If the pack should appear in greenfield choices, add it to GREENFIELD_STACKS
6. Packs sharing the same repo are batched into a single npx skills add invocation

Skill Discovery

The skill_discovery preference controls how GSD finds skills during auto mode:

Mode	Behavior
auto	Skills are found and applied automatically
suggest	Skills are identified but require confirmation (default)
off	No skill discovery

Skill Preferences

Control which skills are used via preferences:

---
version: 1
always_use_skills:
  - debug-like-expert
prefer_skills:
  - frontend-design
avoid_skills:
  - security-docker
skill_rules:
  - when: task involves Clerk authentication
    use: [clerk]
  - when: frontend styling work
    prefer: [frontend-design]
---

Resolution Order

Skills can be referenced by:

1. Bare name — e.g., frontend-design → scans ~/.agents/skills/ and project .agents/skills/
2. Absolute path — e.g., /Users/you/.agents/skills/my-skill/SKILL.md
3. Directory path — e.g., ~/custom-skills/my-skill → looks for SKILL.md inside

Global skills (~/.agents/skills/) take precedence over project skills (.agents/skills/).

Custom Skills

Create your own skills by adding a directory with a SKILL.md file:

~/.agents/skills/my-skill/
  SKILL.md           — instructions for the LLM
  references/        — optional reference files

The SKILL.md file contains instructions the LLM follows when the skill is active. Reference files can be loaded by the skill instructions as needed.

Project-Local Skills

Place skills in your project for project-specific guidance:

.agents/skills/my-project-skill/
  SKILL.md

Project-local skills can be committed to version control so team members share the same skill set.

Skill Lifecycle Management

GSD tracks skill performance across auto-mode sessions and surfaces health data to help you maintain skill quality.

Skill Telemetry

Every auto-mode unit records which skills were available and actively loaded. This data is stored in metrics.json alongside existing token and cost tracking.

Skill Health Dashboard

View skill performance with /gsd skill-health:

/gsd skill-health              # overview table: name, uses, success%, tokens, trend, last used
/gsd skill-health rust-core    # detailed view for one skill
/gsd skill-health --stale 30   # skills unused for 30+ days
/gsd skill-health --declining  # skills with falling success rates

The dashboard flags skills that may need attention:

• Success rate below 70% over the last 10 uses
• Token usage rising 20%+ compared to the previous window
• Stale skills unused beyond the configured threshold

Staleness Detection

Skills unused for a configurable number of days are flagged as stale and can be automatically deprioritized:

---
skill_staleness_days: 60   # default: 60, set to 0 to disable
---

Stale skills are excluded from automatic matching but remain invokable explicitly via read.

Heal-Skill (Post-Unit Analysis)

When configured as a post-unit hook, GSD can analyze whether the agent deviated from a skill’s instructions during execution. If significant drift is detected (outdated API patterns, incorrect guidance), it writes proposed fixes to .gsd/skill-review-queue.md for human review.

Key design principle: skills are never auto-modified. Research shows curated skills outperform auto-generated ones significantly, so the human review step is critical.