Every connection has a port.

What is a network port?

A port is a 16-bit number (0 to 65535) that lets a single computer expose multiple network services on one IP address. Every TCP and UDP packet carries a destination port; the operating system uses it to deliver the packet to the right program. When your browser fetches a webpage, it's connecting to port 443 (HTTPS) on the server. When your mail client checks for new messages, it's talking to port 993 (IMAPS). The convention 'web on 80, mail on 25' is what makes the internet navigable.

What are the three port ranges?

System ports (0-1023) are reserved for well-known services — SSH, HTTP, DNS, and similar foundational protocols. Binding to these ports traditionally requires administrative privileges on Unix systems. Registered ports (1024-49151) are assigned to user-level services and applications — databases, application servers, messaging brokers. Dynamic ports (49152-65535) are used by operating systems for short-lived outbound connections — when your laptop talks to a website, your end of the connection uses a dynamic port.

What does this tool show?

Enter a port we've profiled and you'll get the assigned service (or services — many ports have multiple TCP/UDP entries), what software typically listens there, an honest security note about how the port behaves in the wild, and links to closely-related ports so you can navigate the protocol landscape one hop at a time.

Where does the port data come from?

Service assignments come from the IANA Service Name and Transport Protocol Port Number Registry, with open-frequency data from nmap-services — the database that tells you how often a given port is actually seen open on the internet, not just what it's officially supposed to do. Hand-written context covers the ~90 highest-traffic ports across web, email, databases, DNS, and infrastructure.