design-patterns

design-patterns

Always-on Gang of Four design-pattern catalog plus Pattern Check (Rule 0) hook enforcement for Claude Code.

• 22 GoF patterns, sourced from refactoring.guru, in skills/design-patterns/references/.
• 10 smell detectors that suggest a pattern when code shape calls for one (Strategy, State, Visitor, Factory Method, Builder, Facade, Adapter, Singleton, Observer, Command, Template Method).
• Cross-file duplicate detector — flags shared shapes across files as strong Strategy/Visitor candidates.
• PreToolUse hook that blocks Write/Edit/MultiEdit on .ts/.tsx files until the agent emits a Pattern check: … preamble.
• Decision-log analyzer (analyze-log.js) — surfaces drift, hotspots, per-path pattern frequency.
• /pattern-review slash command — on-demand cross-file project audit.

Tier 1 (preferred first): Factory Method, Abstract Factory, Builder, Singleton, Adapter, Facade, Strategy, Observer, Iterator, Template Method.

---

Requirements

• Node.js ≥ 18 (the hooks are pure stdlib, no npm install needed).
• Claude Code (any recent version supports plugins; older versions can use the symlink installer below).

---

Install

Path A — Claude Code plugin (recommended)

/plugin marketplace add wolffyx/design-patterns
/plugin install design-patterns@design-patterns

Restart Claude Code. The plugin's hooks resolve via ${CLAUDE_PLUGIN_ROOT}, so no path patching or symlinks are needed. Update with /plugin update design-patterns.

Path B — symlink installer

git clone https://github.com/wolffyx/design-patterns.git ~/design-patterns
cd ~/design-patterns
./install.sh

What it does:

• backs up any existing ~/.claude/skills/design-patterns and ~/.claude/hooks to ~/.claude/backups/design-patterns-<ts>/,
• symlinks the repo's skills/design-patterns/ and hooks/ into ~/.claude/,
• merges the hooks block from settings.example.json into ~/.claude/settings.json (substituting $HOME with the user's home).

Restart Claude Code afterwards.

Path C — curl | bash one-liner

curl -fsSL https://raw.githubusercontent.com/wolffyx/design-patterns/main/install.sh \
  | bash -s -- --auto-clone

The --auto-clone flag lets install.sh git-clone itself into ~/design-patterns before running the rest of the steps.

Security note: piping a remote script into bash runs whatever the upstream serves at that moment. Audit the script first if you don't trust the source: open the URL in a browser before running.

Path D — other AI agents (Cursor / Aider / Codex / …)

Hooks are Claude Code-specific (the PreToolUse / PostToolUse API only exists there). The catalog is plain markdown and works anywhere:

cat dist/skill-bundle.md   # 113 KB, self-contained

Drop the contents into:

• Cursor: .cursor/rules/design-patterns.mdc (or paste into Cursor settings → Rules)
• Aider: aider --read dist/skill-bundle.md
• Codex / ChatGPT custom GPT: paste into the system prompt
• Continue / Cline / etc.: their rules / system-prompt slot

---

Uninstall

~/design-patterns/uninstall.sh

Removes the symlinks, restores any backed-up real directories, strips pattern-related entries from ~/.claude/settings.json hooks block.

For plugin installs use:

/plugin uninstall design-patterns@design-patterns

---

Per-project setup

The hooks work without per-project config, but you'll get the most value by adding three things to your repo:

# 1. paste Rule 0 at the top of CLAUDE.md
cat ~/design-patterns/docs/CLAUDE.rule0.md >> CLAUDE.md

# 2. project pattern catalogue (template — fill in as families stabilise)
mkdir -p .claude
cp ~/design-patterns/docs/design-patterns-project-usage.md .claude/

# 3. tunable config (optional)
cp ~/design-patterns/pattern-check.config.example.json .claude/pattern-check.config.json

The config file's $schema ref gives editor autocomplete for every tunable in pattern-check.schema.json.

---

Hooks

Event	Hook	Blocking?	Purpose
SessionStart	session-start-reminder.js	no	Inject Rule 0 banner once per session
UserPromptSubmit	user-prompt-reminder.js	no	Brief reminder on each prompt
PreToolUse	pattern-context-prep.js	no	Sibling-class hint, recent decisions
PreToolUse	check-pattern-preamble.js	yes	Reject Write/Edit/MultiEdit without Pattern check: … preamble
PostToolUse	pattern-smell-detector.js	no	Emit smell suggestions to stderr
PostToolUse	log-pattern-decision.js	no	Append decision to pattern-decision-log.jsonl