Random TCP/UDP Port Generator — Free
Runs 100% in your browser — your files never leave your device.
Local services, test containers, and examples often need a plausible unused-looking port number. Set the minimum and maximum, then generate an unbiased cryptographically random integer inside that range. Availability still depends on your own machine.
How it works
- 1
Set the port range
- 2
Generate a random port
- 3
Copy and check availability locally
About this tool
The port ranges that matter
Ports 0–1023 are system-reserved, 1024–49151 are registered to known services, and 49152–65535 are the dynamic range meant for ephemeral and private use. The generator picks from the dynamic range, where collisions with real services are unlikely and local binding is safe.
When you need a fresh port
Local dev servers that avoid colliding with each other, test instances run side by side, Docker host mappings, and load-test targets all need ports nobody else claims. A generated port beats picking 3000 and hitting whatever already owns it.
Check before you bind
Generation avoids known services, not your own machine's current state — something may already hold the port. The generator cannot see your live listeners; a quick check with your OS's port tooling before committing saves a confusing "address already in use".
Frequently asked questions
Why avoid ports below 1024?
They are privileged (binding needs admin rights) and reserved for system services — ports like 80, 443, and 22 already have owners. The dynamic range exists precisely for everything else.
Can two programs on different machines use the same port?
Yes — port numbers are per-machine. Collisions only matter locally, which is why generation plus a local check is the full workflow.
Are generated ports safe to expose publicly?
Treat any public port as an attack surface regardless of its number — a random port is obscure, not protected. Firewalls and authentication do the security work.