Architecture

Streamlit apps have a client-server structure. The Python backend of your app is the server. The frontend you view through a browser is the client. When you develop an app locally, your computer runs both the server and the client. If someone views your app across a local or global network, the server and client run on different machines.

Python backend (server)

When you execute the command streamlit run your_app.py, your computer uses Python to start up a Streamlit server. The machine where the app initialized with streamlit run is also called a host.

Browser frontend (client)

When someone views your app through a browser, their device acts as a Streamlit client. When you view your app from the same computer where you are running or developing your app, then server and client are coincidentally running on the same machine.