How do I look up what a port number is used for?

How port numbers are organized

A port identifies which service on a machine a connection is for, from 0 to 65535. The low range, 0 to 1023, holds the well-known assignments that core protocols standardized on, the middle range holds registered service ports, and the top of the range is used for ephemeral client connections. That is why seeing port 22 open suggests SSH and why development servers pick high ports like 8080 that need no special privileges.

When you need the lookup

Reading firewall rules, interpreting a port scan of your own machine, debugging why a connection fails, or deciding what a process listening on an unfamiliar port might be, all start with the same question: what normally runs on this port? A lookup tool answers by number or by service name, and works offline in the browser, so you can check ports from a network diagram or an internal audit without that information going anywhere.

Conventions, not guarantees

A port number is a convention: nothing stops a service from running HTTP on 22 or SSH on 8080. Treat the lookup as the standard expectation, and verify what actually answers on the port when it matters.

Step by step

1. Open the lookup. Open the well-known ports lookup in your browser.
2. Search by number or name. Type a port number like 3306, or a service name like postgres.
3. Read the assignment. See which service conventionally uses that port over TCP or UDP.