# Port Number Lookup

- **URL:** https://codeasystem.com/calculators/developer/port-number-lookup/
- **Category:** developer
- **Description:** Identify which well-known service listens on a TCP/UDP port number, drawn from a static table of common assignments.
- **Primary output:** Port 443: https

## Inputs
- Port number (name: `port`, type: number, example: 443)

## Outputs
- Port 443: https
- Protocols: tcp
- Description: HTTP over TLS/SSL
- Range: Well-known (system) ports 0–1023

## Formula / methodology
```
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.

## How to use
1. **Enter the port number**; From a netstat line, firewall rule, error message or security scan.
2. **Read service and protocols**; Results include transport protocols wherever the assignment spans both TCP and UDP.

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

Result for these inputs:

```
Port 443: https
```

## About this calculator
### 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.

## FAQs
### 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).

## Related calculators
- [Subnet & CIDR Calculator](https://codeasystem.com/calculators/developer/subnet-cidr-calculator/)
- [IP Address Format Converter](https://codeasystem.com/calculators/developer/ip-converter/)
- [MIME Type Lookup](https://codeasystem.com/calculators/developer/mime-type-lookup/)

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Last updated: 2026-08-23 · Version: 1.0.0 · [HTML version](https://codeasystem.com/calculators/developer/port-number-lookup/)