My app runs on port 3000; why is it not listed?

Development servers pick arbitrary registered ports. Only widely standardized assignments appear here.

Are UDP and TCP assignments always paired?

Often but not always; DNS uses both, while HTTP is effectively TCP-only (plus QUIC over UDP/443).

Why do ports below 1024 need root?

Unix reserves the privileged range so ordinary users cannot impersonate system services like SSH (22) or HTTPS (443).

Developer & Tech

Port Number Lookup

What this does

Identify which well-known service listens on a TCP/UDP port number, drawn from a static table of common assignments.

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Runs in your browser

How to use it

Using the port number lookup

01
Enter the port number
From a netstat line, firewall rule, error message or security scan.
02
Read service and protocols
Results include transport protocols wherever the assignment spans both TCP and UDP.

Good to know

Port ranges at a glance

0–1023; well-known/system ports, privileged on Unix
1024–49151; registered ports for vendor software
49152–65535; dynamic/ephemeral ports used for outbound connections

Security implications

A listening port is an attack surface regardless of its label. Attackers routinely run services on unexpected ports to evade casual scanning, so treat unknown open ports as findings to investigate, not noise.

How it's calculated

The math behind this calculator

static well-known port table lookup (IANA assignments)

Your number is matched against a static table of widely used IANA assignments covering web, mail, database and infrastructure services. Ports outside the table are reported honestly as unassigned rather than guessed at.

Assumptions & limitations

Static reference table covering common services only.
Services can be reconfigured onto any free port.
Absence from the table does not imply a port is unused or safe.

Worked example

Port 443 carries HTTPS; HTTP wrapped in TLS; over TCP, sitting in the well-known system range below 1024.

FAQ

Frequently asked questions

My app runs on port 3000; why is it not listed?: Development servers pick arbitrary registered ports. Only widely standardized assignments appear here.
Are UDP and TCP assignments always paired?: Often but not always; DNS uses both, while HTTP is effectively TCP-only (plus QUIC over UDP/443).
Why do ports below 1024 need root?: Unix reserves the privileged range so ordinary users cannot impersonate system services like SSH (22) or HTTPS (443).

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