Port Reference: What's Using Each Port and Is It Safe to Kill?

A port number tells your Mac which process should receive a piece of network traffic. When you spot an unfamiliar port in a monitor, a firewall log, or an “address already in use” error, the question is always the same: what is that, and can I close it?

This reference answers it one port at a time. Each page covers what normally listens on the port, what that service actually does, whether it’s safe to kill, whether its presence is a red flag, and the exact command to find and free it on macOS.

How port numbers are organized

IANA splits the 0-65535 range into three bands:

• Well-known ports (0-1023): Core services like HTTP (80), HTTPS (443), and SSH (22). Binding one requires admin privileges.
• Registered ports (1024-49151): Assigned to specific applications such as MySQL (3306) or PostgreSQL (5432), but any process can bind them.
• Dynamic / ephemeral ports (49152-65535): Handed out automatically for outgoing connections. Seeing many of these is normal.

For the full categorized table, see Common ports and what they’re used for. If a dev server won’t start because the port is taken, the port already in use guide covers the fix.

Find what’s on a port in two seconds

Every page here shows the manual lsof command. If you’d rather see every open port and its owning app in one window, Portie lists them live and lets you kill a process without touching Terminal.