/existing-repo

name: existing-repo
description: Analyze existing repositories, maintain structure, setup guardrails and best practices
when-to-use: When working with an existing codebase for the first time or adding guardrails
user-invocable: true
allowed-tools: [Read, Glob, Grep, Bash]
effort: high

Existing Repository Skill

For working with existing codebases - analyze structure, respect conventions, and set up proper guardrails without breaking anything.

**Sources:** [Husky](https://typicode.github.io/husky/) | [lint-staged](https://github.com/lint-staged/lint-staged) | [pre-commit](https://pre-commit.com/) | [commitlint](https://commitlint.js.org/)

---

Core Principle

**Understand before modifying.** Existing repos have conventions, patterns, and history. Your job is to work within them, not reorganize them.

---

Phase 1: Repository Analysis

**ALWAYS run this analysis first when joining an existing repo.**

1.1 Basic Detection

# Check git status
git remote -v 2>/dev/null
git branch -a 2>/dev/null
git log --oneline -5 2>/dev/null

# Check for existing configs
ls -la .* 2>/dev/null | head -20
ls *.json *.toml *.yaml *.yml 2>/dev/null

1.2 Tech Stack Detection

# JavaScript/TypeScript
ls package.json tsconfig.json 2>/dev/null

# Python
ls pyproject.toml setup.py requirements*.txt 2>/dev/null

# Mobile
ls pubspec.yaml 2>/dev/null          # Flutter
ls android/build.gradle 2>/dev/null   # Android
ls ios/*.xcodeproj 2>/dev/null        # iOS

# Other
ls Cargo.toml 2>/dev/null             # Rust
ls go.mod 2>/dev/null                 # Go
ls Gemfile 2>/dev/null                # Ruby

1.3 Repo Structure Type

| Pattern | Detection | Meaning | |---------|-----------|---------| | **Monorepo** | `packages/`, `apps/`, `workspaces` in package.json | Multiple projects, shared tooling | | **Full-Stack Monolith** | `frontend/` + `backend/` in same repo | Single team, tightly coupled | | **Separate Concerns** | Only frontend OR backend code | Split repos, separate deploys | | **Microservices** | Multiple `service-*` or domain dirs | Distributed architecture |

# Detect repo structure type
if [ -d "packages" ] || [ -d "apps" ]; then
    echo "MONOREPO detected"
elif [ -d "frontend" ] && [ -d "backend" ]; then
    echo "FULL-STACK MONOLITH detected"
elif [ -d "src" ] || [ -d "app" ]; then
    # Check if it's frontend or backend
    grep -q "react\|vue\|angular" package.json 2>/dev/null && echo "FRONTEND detected"
    grep -q "fastapi\|express\|django" package.json pyproject.toml 2>/dev/null && echo "BACKEND detected"
fi

1.4 Directory Mapping

# Get directory structure (max 3 levels)
find . -type d -maxdepth 3 \
    -not -path "*/node_modules/*" \
    -not -path "*/.git/*" \
    -not -path "*/venv/*" \
    -not -path "*/__pycache__/*" \
    -not -path "*/dist/*" \
    -not -path "*/build/*" \
    2>/dev/null | head -50

# Identify key directories
for dir in src app lib core services api routes components pages hooks utils models; do
    [ -d "$dir" ] && echo "Found: $dir/"
done

1.5 Entry Points

# Find main entry points
ls index.ts index.js main.ts main.py app.py server.ts server.js 2>/dev/null
cat package.json 2>/dev/null | grep -A1 '"main"'
cat pyproject.toml 2>/dev/null | grep -A1 'scripts'

---

Phase 2: Convention Detection

**Identify and document existing patterns before making changes.**

2.1 Code Style

# Check for formatters
ls .prettierrc* .editorconfig .eslintrc* biome.json 2>/dev/null  # JS/TS
ls pyproject.toml | xargs grep -l "ruff\|black\|isort" 2>/dev/null  # Python

# Check indent style from existing files
head -20 src/**/*.ts 2>/dev/null | grep "^\s" | head -1  # tabs vs spaces

2.2 Testing Setup

# JS/TS testing
grep -l "jest\|vitest\|mocha\|playwright" package.json 2>/dev/null
ls jest.config.* vitest.config.* playwright.config.* 2>/dev/null

# Python testing
grep -l "pytest\|unittest" pyproject.toml 2>/dev/null
ls pytest.ini conftest.py 2>/dev/null

# Test directories
ls -d tests/ test/ __tests__/ spec/ 2>/dev/null

2.3 CI/CD Setup

# Check existing workflows
ls -la .github/workflows/ 2>/dev/null
ls .gitlab-ci.yml Jenkinsfile .circleci/ 2>/dev/null

# Check deploy configs
ls vercel.json render.yaml fly.toml railway.json Dockerfile 2>/dev/null

2.4 Documentation Style

# Find README pattern
head -30 README.md 2>/dev/null

# Find existing docs
ls -la docs/ documentation/ wiki/ 2>/dev/null
ls CONTRIBUTING.md CHANGELOG.md 2>/dev/null

---

Phase 3: Guardrails Audit

**Check what guardrails exist and what's missing.**

3.1 Pre-commit Hooks Status

# Check for hook managers
ls .husky/ 2>/dev/null && echo "Husky installed"
ls .pre-commit-config.yaml 2>/dev/null && echo "pre-commit framework installed"
ls .git/hooks/pre-commit 2>/dev/null && echo "Manual pre-commit hook exists"

# Check what hooks run
cat .husky/pre-commit 2>/dev/null
cat .pre-commit-config.yaml 2>/dev/null

3.2 Linting Status

# JS/TS linting
grep -q "eslint" package.json && echo "ESLint configured"
grep -q "biome" package.json && echo "Biome configured"
ls .eslintrc* biome.json 2>/dev/null

# Python linting
grep -q "ruff" pyproject.toml && echo "Ruff configured"
grep -q "flake8" pyproject.toml setup.cfg && echo "Flake8 configured"

3.3 Type Checking Status

# TypeScript
ls tsconfig.json 2>/dev/null && echo "TypeScript configured"
grep "strict" tsconfig.json 2>/dev/null

# Python type checking
grep -q "mypy" pyproject.toml && echo "mypy configured"
grep -q "pyright" pyproject.toml && echo "pyright configured"
ls py.typed 2>/dev/null

3.4 Commit Message Enforcement

# commitlint
ls commitlint.config.* 2>/dev/null && echo "commitlint configured"
cat .husky/commit-msg 2>/dev/null
grep "conventional" package.json 2>/dev/null

3.5 Security Scanning

# Check for security tools
grep -q "detect-secret