localhost:8501: Streamlit apps
Port 8501 is Streamlit’s default. How to open your app, change the port and fix errors.
Open this address: http://localhost:8501This opens on your own computer. It only works if the program is running.
localhost:8501 is the default address of a Streamlit app. It works while the streamlit command keeps running in your terminal.
What runs on localhost:8501
- Streamlit apps started with
streamlit run
Commands to start and test port 8501
streamlit run app.pystreamlit run app.py --server.port 8502streamlit run app.py --server.address 0.0.0.0Find what is using port 8501
Run these in a terminal on your computer. Nothing is sent to this site.
If localhost:8501 will not open
- Port 8501 is already in use
- An older Streamlit app is still running. Stop it, or start the new one with
--server.port 8502. - streamlit: command not found
- Install it with
pip install streamlitand activate the right Python environment. - Blank page
- Read the terminal for Python errors. Streamlit shows them there and in the page.
- Cannot open it from your phone
- Use
--server.address 0.0.0.0and your computer’s IP address. See how to open localhost from your phone.
Other ports like 8501
| Port | Usually used by |
|---|---|
| localhost:3000 | React, Next.js, Express |
| localhost:5173 | Vite dev server |
| localhost:4200 | Angular dev server |
| localhost:5000 | Flask |
| localhost:8000 | Django, PHP, Python |
| localhost:8080 | Tomcat, Spring Boot, Docker |
| localhost:8888 | Jupyter Notebook |
Questions about localhost:8501
- What is port 8501?
- The default port of Streamlit apps.
- How do I run two Streamlit apps?
- Start the second with a different port, such as --server.port 8502.
- Is localhost:8501 safe?
- Yes, as long as it stays on localhost. Only your own computer can reach localhost:8501. It becomes reachable from other devices only if you start the program on 0.0.0.0 or your computer's IP address. Development servers are for testing, so do not put them on the public internet.
- Can I use a different port instead of 8501?
- Yes. Most programs let you choose the port with a setting or a command option. Pick a free port above 1024 and open that number instead, for example localhost:8502.
- How do I check what is using port 8501?
- Use the port checker on this page. It shows the command for Windows, macOS and Linux and does not send anything to this site.
- Can I open localhost:8501 from my phone?
- Yes, if both are on the same Wi-Fi. Start the program so it listens on all addresses, then open your computer's IP address with :8501 on the phone. A firewall on the computer can still block it.
Free tools that help
- Common ports listSearch a list of common TCP and UDP port numbers: SSH 22, HTTP 80, HTTPS 443, MySQL 3306, PostgreSQL 5432 and more, with dev server ports.