If you’re seeing the error “Arize Phoenix is not running on http://127.0.0.1:6006/”, it means the Phoenix server is not starting properly or cannot be accessed at the expected local address. This issue can occur due to various reasons, including incorrect configurations, firewall restrictions, dependency issues, or conflicts with existing processes.

In this guide, we’ll cover:

• What the error means
• Common causes
• Step-by-step solutions
• Best practices to avoid future issues
• Frequently asked questions (FAQs)

By the end of this guide, you’ll know exactly how to fix and prevent this issue, ensuring your Arize Phoenix instance runs smoothly.

What is Arize Phoenix?

Arize Phoenix is an open-source observability tool for AI and ML models, helping users trace, debug, and monitor LLM applications and embeddings. It provides a local server (default http://127.0.0.1:6006/) where users can visualize and analyze their AI traces.

What Does This Error Mean?

When you see the error “Arize Phoenix is not running on http://127.0.0.1:6006/”, it means the local Phoenix server:

Did not start successfully
Crashed after launching
Cannot be accessed due to network or firewall restrictions

This means you won’t be able to use Phoenix’s tracing, observability, or debugging features until the issue is resolved.

Common Causes of the Error

Here are the most common reasons why Arize Phoenix is not running on http://127.0.0.1:6006/:

1. The Phoenix Server is Not Started

You may have forgotten to start the Phoenix server before accessing the URL.

2. Port 6006 is Blocked or Already in Use

Another process (such as TensorBoard) might be using port 6006, preventing Phoenix from running.

3. Firewall or VPN Restrictions

Your firewall, VPN, or network settings might be blocking local connections.

4. Python Environment Issues

If you’re running Phoenix in Jupyter Notebook or a virtual environment, missing dependencies or incorrect installations can cause issues.

5. Missing or Corrupt Installation

An incomplete Phoenix installation may prevent the server from running properly.

How to Fix “Arize Phoenix is Not Running on http://127.0.0.1:6006/”

Follow these steps one by one to troubleshoot and resolve the issue.

Step 1: Check if Phoenix is Installed Correctly

Run this command in your terminal:

sh

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pip list | grep phoenix

If Phoenix is not installed, install it using:

sh

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pip install arize-phoenix

If it’s already installed but outdated, upgrade it:

sh

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pip install –upgrade arize-phoenix

Now, try starting the server again:

python

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import phoenix as px

px.launch()

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Step 2: Manually Start the Phoenix Server

Instead of relying on automatic startup, try launching the Phoenix server manually:

python

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import phoenix as px

server = px.launch()

print(server)

If you see an error message, read it carefully to identify the problem.

Step 3: Check if Port 6006 is Already in Use

Run the following command to see if another process is using port 6006:

sh

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lsof -i :6006

If the output shows another process using 6006, stop it:

sh

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kill -9 <PROCESS_ID>

Then, try starting Phoenix again.

Step 4: Run Phoenix on a Different Port

If port 6006 is occupied and you don’t want to stop other processes, start Phoenix on a different port:

python

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px.launch(port=7000)

Now, access it at http://127.0.0.1:7000/ instead.

Step 5: Disable Firewall or VPN

If you’re using a firewall or VPN, it might be blocking the connection. Try:
Disabling the VPN temporarily
Allowing local connections in firewall settings

On macOS/Linux, you can check firewall settings with:

sh

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sudo ufw status

On Windows, try disabling Windows Defender Firewall temporarily and check if Phoenix starts.

Step 6: Reinstall Phoenix and Restart the System

If none of the above steps work, completely reinstall Phoenix:

sh

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pip uninstall arize-phoenix -y

pip install arize-phoenix

Then, restart your system and try running Phoenix again.

Best Practices to Avoid This Issue in the Future

1. Always check if Phoenix is running before accessing the URL.
2. Use a dedicated Python environment to prevent conflicts.
3. Restart your machine occasionally to free up blocked ports.
4. Regularly update Phoenix to ensure compatibility with new dependencies.
5. Use alternative ports if port 6006 is frequently used by other applications.

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Frequently Ask Question

1. How do I check if Phoenix is running?

Run:

sh

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ps aux | grep phoenix

If it’s running, you should see a process ID. If not, the server is not active.

2. Can I run Phoenix on a remote machine?

Yes, but you need to start it with:

python

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px.launch(host=”0.0.0.0″, port=6006)

Then, access it via http://your-ip:6006/ from another device.

3. What if Phoenix crashes after launching?

Try checking the logs:

sh

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tail -f ~/.phoenix/logs

This will show you any errors causing the crash.

4. How do I free up port 6006?

Run:

sh

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lsof -i :6006

kill -9 <PROCESS_ID>

Then, restart Phoenix.

5. How do I completely reset Phoenix?

To clear all configurations and restart fresh:

sh

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rm -rf ~/.phoenix

pip uninstall arize-phoenix -y

pip install arize-phoenix

Conclusion

The “Arize Phoenix is not running on http://127.0.0.1:6006/” error usually happens due to incorrect installation, port conflicts, firewall restrictions, or missing dependencies.

By following this guide, you should be able to troubleshoot, fix, and prevent this issue effectively. 

 Key Takeaways:

• Ensure Phoenix is installed and running before accessing the URL.
• Check for port conflicts and use an alternative port if needed.
• Disable VPNs and firewalls if they’re blocking connections.
• Reinstall Phoenix if other solutions don’t work.