Random Port Generator

Generate random TCP/UDP port numbers in any range — well-known, registered, dynamic, or custom.

Port range

Count: 5

Common port reference

SSH

HTTP

443

HTTPS

3306

MySQL

5432

PostgreSQL

6379

Redis

27017

MongoDB

8080

HTTP-alt

8443

HTTPS-alt

TCP/UDP port ranges

Port numbers range from 0 to 65535. Ports 0–1023 are well-known ports assigned by IANA to common services (HTTP, HTTPS, SSH). Ports 1024–49151 are registered ports used by applications. Ports 49152–65535 are dynamic/ephemeral ports typically used for client-side connections. This tool generates cryptographically random port numbers using crypto.getRandomValues.

Built and maintained by Meet Shah · Last updated 19 July 2026

What this tool is used for

Picking a port for a local development server that is unlikely to be in use.
Choosing a port in the dynamic range for a temporary service.
Generating a port for a test that spins up a listener.
Producing values to populate a config fixture.
Avoiding a collision with a service you already have running.

Frequently Asked Questions

Which port ranges are safe to use?: 49152-65535, the IANA dynamic/private range reserved for exactly this. 0-1023 are well-known ports needing root on Unix; 1024-49151 are registered to specific services and may collide with something installed.
What is the ephemeral port range?: The range the OS draws from for outbound connections — commonly 32768-60999 on Linux and 49152-65535 on Windows. Binding a server inside it risks an intermittent conflict when the OS has already taken that port.
Which ports should I avoid?: Browsers block a list outright (including 25, 110, 143 and 6000) as ERR_UNSAFE_PORT, so a dev server there is unreachable from a browser regardless of whether it binds successfully.
Why do the same dev ports keep recurring?: Convention, not requirement: 3000 for Node, 8000 and 8080 for HTTP alternates, 5432 Postgres, 3306 MySQL, 6379 Redis. Their familiarity is exactly why they collide when several projects run at once.
How do I check a port is actually free?: This generates a number; it cannot test availability from a browser. Use lsof -i :PORT or netstat -an, or bind with port 0 and let the OS assign a free one — the only race-free method.
Why does a port stay unusable after the process exits?: Because the socket sits in TIME_WAIT for up to a couple of minutes, guaranteeing stray packets are not delivered to a new listener. `SO_REUSEADDR` is what lets a server rebind immediately.
How do I get a guaranteed-free port in a test?: Bind to port 0 and read back the one the OS assigned. Picking a random number and hoping is racy — another process can take it between the check and the bind.

Common errors and gotchas

Picking a port below 1024, which needs elevated privileges on most systems.
Choosing a well-known port and colliding with a service that is already listening.
Assuming a random port is free, which only actually binding it can establish.
Hard-coding a randomly chosen port into a config, which defeats the point of choosing dynamically.
Overlooking that a firewall or a container may not expose the range you picked from.