How to deploy a Flask app for free.

The short answer

To deploy a Flask app for free, give your coding agent the sentence below. Antideploy finds Flask in your requirements, finds the file that creates your app, and starts it. Add gunicorn to requirements.txt so Antideploy runs it with gunicorn. Without it, Antideploy falls back to Flask's built-in server, which works but is meant for development, not real traffic.

What Antideploy detects

• Flask. Detected from flask in requirements.txt or pyproject.toml.
• The start command. With gunicorn, waitress or uwsgi in your requirements: gunicorn module:app --bind 0.0.0.0:$PORT. Without one: python -m flask --app module run --host 0.0.0.0 --port $PORT, and a warning.
• The module. The file that contains app = Flask(. If none is found, it uses app.
• The port. It starts the app with PORT set.
• The Python version. From .python-version, runtime.txt or requires-python in pyproject.toml.

What your project needs

flask
gunicorn
psycopg[binary]

import os
import psycopg
from flask import Flask

app = Flask(__name__)

@app.get("/health")
def health():
    return "ok"

# Do not call app.run() here. The start command runs the app.

You do not need to call app.run() or choose a host and port in code. The start command passes 0.0.0.0 and PORT. If you do call app.run() for local use, keep it under if __name__ == "__main__":.

Step by step

1. Add gunicorn

   Add gunicorn to requirements.txt. It is the production server for Flask.

2. Paste the sentence and approve one link

   Your agent creates the app and, if your code uses Postgres, the database. It writes the connection details into your .env without printing them.

3. Deploy and open the link

   Antideploy installs your requirements, starts the app and checks that it answers. Your agent tells you the address.

Common problems

• The app never starts listening. A gunicorn command with the wrong module name, or a crash on startup. The deploy shows what the app printed before it exited. See never started listening.
• No module named. A package your code imports is not in requirements.txt. See ModuleNotFoundError.
• A package fails to compile. See Failed building wheel.
• Uploads or a SQLite file disappear. The disk is replaced on every deploy. Use a bucket and Postgres.