Troubleshooting

"Port already in use"

Another process is already listening on the port the app wants. Either stop that process or change the port:

npm run dev -- -p 3001

Dependency install fails

Delete the lockfile-derived install artifacts and reinstall cleanly:

rm -rf node_modules
npm install

For Python projects, make sure you're inside the correct virtual environment before installing:

python -m venv venv
venv\Scripts\activate   # Windows
pip install -r requirements.txt

"Missing environment variable" errors

Check that .env exists (not just .env.example) and that every variable referenced in the code has a value set.

Database connection errors

Confirm the database service is actually running and that DATABASE_URL points to the right host, port, and credentials. For Docker-based projects, check the container status:

docker compose ps
docker compose logs -f

Still stuck?

Open an issue on the relevant project's GitHub repository with your OS, the exact command you ran, and the full error message — see Contact for links.