Flask Cheat Sheet

Flask cheat sheet with real commands and snippets for setup, core workflows, debugging, and production-safe automation patterns. If you are working across tools, pair this with the Python Cheat Sheet and Pytest Cheat Sheet.

Setup and Installation

Goal: Create a fresh project

# Scaffold project using official starter
python -m venv .venv && source .venv/bin/activate

# Install dependencies after scaffold completes
pip install flask

Goal: Verify local toolchain versions

# Print Node.js runtime version
node --version

# Print npm version for lockfile consistency
npm --version

# Inspect package scripts in project
cat package.json | rg "scripts" -n

Core Development Workflow

Goal: Run local development server

# Start framework dev server with hot reload
flask --app app run --debug

# Check local endpoint health
curl -I http://localhost:3000 || curl -I http://localhost:5173 || true

Goal: Build and preview production output

# Build optimized production assets
pytest

# Run production preview server
curl -I http://127.0.0.1:5000/health

Goal: Implement a core feature snippet

# Minimal Flask health endpoint
from flask import Flask, jsonify

app = Flask(__name__)

@app.get('/health')
def health():
    return jsonify(ok=True)

Testing and Quality

Goal: Run tests and static checks

# Execute project tests
pytest

# Run type checking when available
npm run check || npx tsc --noEmit || true

# Run linting for fast feedback
npm run lint || true

Deployment and Operations

Goal: Prepare deployment artifacts

# Create production build before deployment
pytest

# Validate environment variables are set
node -e "console.log('NODE_ENV=', process.env.NODE_ENV || 'unset')"

# Smoke-test production route after deploy
curl -I https://devcheatsheets.com

Debugging and Troubleshooting

Goal: Inspect build and runtime failures

# Reinstall dependencies from lockfile
rm -rf node_modules && npm ci

# Re-run build with clean cache
npm run build

# Search source for suspect route/config patterns
rg "route|middleware|config" src app -n

Common Gotchas

• Run Flask builds locally before shipping to CI/CD environments.
• Keep environment secrets outside the repository and load them per environment.
• Avoid stale dependency locks by using npm ci in automation.
• Validate route and middleware behavior with explicit smoke tests.
• Keep framework and plugin versions aligned to avoid build regressions.

Related Sheets

• Python Cheat Sheet — scripts, APIs, and automation tasks.
• Pytest Cheat Sheet — daily Pytest commands and production-ready examples.
• htmx Cheat Sheet — daily htmx commands and production-ready examples.