Python

Framework	Detected by	Started with
Streamlit	streamlit in your dependencies	streamlit run, mounted under your app’s path
FastAPI	fastapi in your dependencies	uvicorn with --root-path set
Flask	flask in your dependencies	gunicorn if your dependencies include it, otherwise flask run — see Flask
marimo	a root .py that imports marimo and builds a marimo.App	marimo run, mounted under your app’s path
Python	anything else	python <entry point>

Dependencies are read from requirements.txt, else pyproject.toml, else Pipfile. marimo as a dependency alone is not the trigger — a Flask app that imports it stays Flask.

Flask

Toft never adds a web server you didn’t ask for. If your dependencies include gunicorn, your Flask app is served by gunicorn; otherwise it runs on Flask’s development server. The build log says which one your app got:

    Serving with gunicorn (app), from this app's requirements.

To move to gunicorn, add gunicorn to requirements.txt and deploy again.

gunicorn needs to know which object is your app. Toft looks in your entry point for a top-level app = Flask(...) (or an object named app or application), then for a create_app() or make_app() factory that takes no arguments. If it finds none, the app runs on Flask’s development server even with gunicorn installed, and the build log says so.

Toft sets the address gunicorn listens on. To choose workers, timeouts and other options, set GUNICORN_CMD_ARGS as an environment variable, for example --workers 4 --timeout 60.

Entry point

Every Python app except marimo needs one of these at the root, picked in this order: app.py, main.py, streamlit_app.py, server.py, wsgi.py. With none, the deploy is refused.

The contract

Listen on PORT, bound to HOST. Toft passes both to Streamlit, FastAPI, Flask and marimo for you; a plain Python app reads them from the environment.

Anything you send to the browser must respect the /apps/<slug> prefix. See Base paths.

Dependencies

Toft creates a virtual environment with uv and installs requirements.txt (uv pip install -r), or, if there’s none, your pyproject.toml project (uv pip install .). A Pipfile is used for detection only. The Toft SDK is installed for you.

Pin your versions. An unpinned requirements.txt resolves differently over time.

Version

toft.toml

[runtime]
python = ">=3.12,<3.14"

See Language versions.

With no pin, requires-python in pyproject.toml is used only when it rules out the install’s default Python. Then Toft builds with the newest version it allows. See Python’s requires-python.

Work that finishes

A web app must keep running — a script that computes something and exits looks like a crash. Run batch work as a job, and have the web app show the result.