Why is port 5000 already in use on Mac?

On macOS Monterey and later, the 'AirPlay Receiver' feature listens on port 5000 by default. You must disable it in System Settings > Sharing to free up the port for Python/Flask.

How to run Flask on a different port?

Change your run command to: 'flask run --port 5001' or modify your app.run() call to specify 'port=5001'.

Localhost 5000: Fix AirPlay Conflict & Flask Errors

Why is Localhost 5000 Forbidden?

Port 5000 has a unique problem compared to other ports: Operating System Conflicts.

1. macOS Users: AirPlay Receiver Conflict

If you are on macOS Monterey or newer, "ControlCenter" is using port 5000 for AirPlay. This prevents Flask from starting.

Option A: Disable AirPlay (Recommended)

Open System Settings > General > AirDrop & Handoff.
Toggle "AirPlay Receiver" to OFF.

Option B: Kill the Process (Temporary)

                    lsof -i :5000

                    # You will see 'ControlCenter'

                    kill -9 [PID]

2. Python Flask Binding

By default, Flask runs on 127.0.0.1:5000. Sometimes accessing via localhost fails due to DNS resolution.

Fix: Try clicking this direct IP link instead:

http://127.0.0.1:5000

Or run Flask on a different port to avoid conflicts completely:

flask run --port 5001

3. Docker Registry

If you are trying to push/pull images locally, ensure the Docker Registry container is actually running.

docker ps | grep registry

If it is not running, start it mapping port 5000:

docker run -d -p 5000:5000 --name registry registry:2