Enforcing Code Standards Across a Multi-Language Team

Code quality at scale requires automation. This guide covers our complete linting and formatting strategy across a polyglot monorepo: ESLint with Turborepo caching, Prettier for formatting, Python tools (Black, Flake8, Isort), and CI/CD enforcement.

Part 1: Scalable Linting with Turborepo & ESLint

Shared Configuration

Instead of copy-pasting .eslintrc.js files, we publish a local @repo/eslint-config package.

• packages/eslint-config/nest.js: Base rules for all NestJS microservices.
• apps/api/.eslintrc.js: Extends the base config.

module.exports = {
  extends: ["@repo/eslint-config/nest.js"]
};
    

Intelligent Caching

Turborepo knows your dependency graph. If you only change the payment service, turbo lint will only re-lint that service, saving minutes on every build.

{
  "pipeline": {
    "lint": {
      "dependsOn": ["^lint"],
      "outputs": []
    }
  }
}
    

Parallel Execution

Running npm run lint executes all lint tasks in parallel. Caching ensures that unchanged services hit the cache instantly.

> turbo run lint
api:lint: cache hit, replaying output...
payment:lint: cache hit, replaying output...
client:lint: cache miss, executing...
    

Part 2: Opinionated Formatting with Prettier

The One Source of Truth

Our format rules are encoded in .prettierrc, respected by IDEs, commit hooks, and CI:

{
  "semi": true,
  "singleQuote": true,
  "trailingComma": "all",
  "printWidth": 100
}
    

ESLint Integration

Using eslint-config-prettier is mandatory to disable conflicting rules:

extends: [
  'plugin:prettier/recommended',
]
    

Beyond JavaScript

We use Prettier for everything:

• JSON: tsconfig.json, package.json
• YAML: docker-compose.yml, GitHub Actions
• Markdown: README.md, Documentation

Part 3: Strict Python Code Quality

Black, Flake8, Isort

Three non-negotiable tools for Python:

• Black: "The Uncompromising Code Formatter". No arguments about spacing.
• Flake8: Catches logic errors and unused imports.
• Isort: Sorts your imports alphabetically and by type.

Centralized Config

[tool.black]
line-length = 88
target-version = ['py311']

[tool.isort]
profile = "black"
line_length = 88
    

Pre-Commit Integration

We use pre-commit hooks to fix issues before they even reach the repo.

# .pre-commit-config.yaml
- repo: https://github.com/psf/black
  rev: 23.3.0
  hooks: [id: black]
    

Part 4: Automating Quality Checks in CI/CD

The Quality Workflow

Local hooks can be bypassed. The CI pipeline is the final arbiter of quality. We run this on every Pull Request.

GitHub Actions Workflow

name: Quality Check
on:
  pull_request:
    branches: [main]

jobs:
  lint-node:
    name: Lint Node.js (ESLint + Prettier)
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 18
          cache: 'npm'
      - run: npm ci
      - run: npx turbo run lint

  lint-python:
    name: Lint Python (Black + Flake8)
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
        with:
          python-version: '3.11'
          cache: 'pip'
      - run: pip install black flake8
      - run: black --check .
      - run: flake8 .
    

Production Tips

• Branch Protection: Configure GitHub Settings to require the Lint Node.js and Lint Python checks to pass before merging. This prevents "broken windows" in your codebase.
• Husky: Use Husky to run linters on pre-commit locally. It saves CI minutes by catching errors before the push.
• Rule Depreciation: Review your ESLint rules every 6 months. If a rule is constantly ignored or disabled, remove it. Rules should help, not hinder.