Lint Check

Quick linting validation (<5 seconds).

Purpose

Run fast linting checks on changed files before commits.

Philosophy: Quick checks only (<5s) + Trust CI for comprehensive validation

When to Use This Skill

Trigger phrases:

• "lint my code"
• "check formatting"
• "run linters"
• "check code quality"

Use when:

• Before committing changes
• Quick validation during development
• Checking specific files

Workflow

1. Detect Changed Files

# Get staged and unstaged changes
git diff --name-only HEAD
git diff --name-only --cached

File categories:

• Frontend: *.ts, *.tsx, *.js, *.jsx
• Backend: *.py
• Config: *.json, *.yaml, *.yml

2. Run Linters by File Type

Frontend (TypeScript/JavaScript):

# ESLint for code quality
npx eslint --max-warnings 0 <files>

# Prettier for formatting
npx prettier --check <files>

Backend (Python):

# Ruff for fast linting (replaces pylint/flake8/black)
ruff check <files>

# Type checking (if mypy available)
mypy <files> 2>/dev/null || true

Config files:

# JSON validation
jq empty <file.json>

# YAML validation
yamllint <file.yaml> 2>/dev/null || true

3. Report Results

Success:

✅ Linting passed!
   Checked: 12 files
   - 8 TypeScript files
   - 3 Python files
   - 1 JSON file

   No issues found.

Failure:

❌ Linting failed!
   Checked: 12 files
   Found: 5 issues

   frontend/src/App.tsx:
     - Line 23: Missing semicolon (eslint)
     - Line 45: Unused variable 'data' (eslint)

   backend/api/routes.py:
     - Line 12: Line too long (89 > 88 characters) (ruff)

   Fix these issues and run again.

4. Exit Fast

No auto-fixing:

• Report issues only
• User fixes manually
• Trust CI for comprehensive checks

Integration Points

With sync-feature-branch

Optional pre-commit check:

# In sync-feature-branch skill
if user wants quick lint:
  lint-check skill
  if fails:
    echo "Fix linting issues before committing"
    exit 1

With Git

Staged files only:

# Only lint what's about to be committed
git diff --cached --name-only | xargs <linter>

Linter Configuration

Frontend (package.json required)

ESLint:

npx eslint --ext .ts,.tsx,.js,.jsx <files>

Prettier:

npx prettier --check <files>

Backend (ruff preferred)

Ruff (fast):

ruff check <files>

Fallback to pylint:

pylint <files>

Best Practices

Do

✅ Run on changed files only (fast) ✅ Report issues clearly ✅ Exit fast (<5s target) ✅ Trust CI for full validation ✅ Use project's linter config (.eslintrc, ruff.toml)

Don't

❌ Auto-fix issues (user fixes manually) ❌ Run on entire codebase (too slow) ❌ Block commits (advisory only) ❌ Run comprehensive type checking (CI does this) ❌ Ignore project config

What This Skill Does

✅ Detects changed files (git diff) ✅ Runs appropriate linters (eslint, ruff, prettier) ✅ Reports issues clearly ✅ Exits fast (<5s) ✅ Respects project linter config

What This Skill DOESN'T Do

❌ Auto-fix issues ❌ Run on entire codebase ❌ Block commits ❌ Run comprehensive type checking ❌ Replace CI validation

Examples

Example 1: Clean Code

User: "lint my code"

lint-check:

1. Detect files:
   - frontend/src/App.tsx
   - frontend/src/utils.ts
   - backend/api/routes.py

2. Run linters:
   - ESLint: ✓ pass (2 files)
   - Ruff: ✓ pass (1 file)

3. Report:
   ✅ Linting passed!
   Checked: 3 files
   No issues found.

Example 2: Issues Found

User: "check formatting"

lint-check:

1. Detect files:
   - frontend/src/Dashboard.tsx
   - backend/services/auth.py

2. Run linters:
   - ESLint: ✗ fail (1 issue)
   - Ruff: ✗ fail (2 issues)

3. Report:
   ❌ Linting failed!

   frontend/src/Dashboard.tsx:
     Line 34: 'data' is assigned but never used (no-unused-vars)

   backend/services/auth.py:
     Line 12: Line too long (92 > 88 characters)
     Line 45: Undefined name 'UserModel'

   Fix these issues and run again.

Example 3: No Changed Files

User: "lint my code"

lint-check:

1. Detect files:
   (no changed files)

2. Report:
   ℹ️  No changed files to lint.

   Stage changes first: git add <files>

Troubleshooting

Linter Not Found

Symptom: eslint: command not found

Fix:

# Install linters
cd frontend && npm install
cd backend && pip install ruff

Config Missing

Symptom: Linter uses default config instead of project config

Check:

ls -la .eslintrc* ruff.toml .prettierrc*

Fix: Use project config if present

Too Slow

Symptom: Takes >5 seconds

Fix: Reduce scope to staged files only

git diff --cached --name-only | xargs <linter>

Related Skills

• sync-feature-branch: May call lint-check before commit
• fix-pr-feedback: May suggest running linters for CI failures

Resources

Linter docs:

• ESLint: https://eslint.org/docs/latest/
• Prettier: https://prettier.io/docs/
• Ruff: https://docs.astral.sh/ruff/
• Pylint: https://pylint.readthedocs.io/

Project config:

• .eslintrc.json - ESLint rules
• .prettierrc - Prettier config
• ruff.toml - Ruff config
• pyproject.toml - Python tools config

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Last Updated: 2025-01-12 Skill Type: Workflow Average Duration: <5 seconds Related Docs:

• AGENTS.md (V3 trust environments)
• .claude/skills/sync-feature-branch/SKILL.md