Random Port Number Generator
Generate random port numbers from the well-known, registered, dynamic, or a custom range. Produces multiple deduplicated ports at once and flags commonly occupied ports so you avoid conflicts.
FreeOnline Tool
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How to Use
- Choose a port range: well-known (1-1023), registered (1024-49151), dynamic (49152-65535), or a custom range.
- Set how many ports you want to generate.
- Click the "Generate" button to get that many random port numbers.
- Copy the ports into your development configuration.
Features
- Generates within a chosen category: well-known, registered, or dynamic ports.
- Supports a custom start and end range for anything else you need.
- Produces several random ports at once with duplicates removed automatically.
- Marks ports that are commonly already taken, such as 80, 443, and 3306, so you can steer clear.
- Includes a reference list of default ports for common services.
Use Cases
Running several local services
Assign each microservice on your machine a random port so nothing collides and the development environment comes up quickly.
Planning Docker port mappings
Generate a batch of random host-side ports when mapping a multi-container application so none of them clash with existing services.
Spinning up test environments
Give each test instance in a CI/CD pipeline a random port so parallel jobs can run without interfering with one another.
Practicing network programming
Use random ports for socket programming exercises to get a feel for how ports work and which conventions protocols follow.
FAQ
How is the port range divided up?
There are 65535 TCP/UDP ports in three groups: well-known ports (0-1023) assigned by IANA to system services, registered ports (1024-49151) for applications, and dynamic or private ports (49152-65535) for ephemeral use.
Which port should I pick for development?
Use an unoccupied port in the registered range (1024-49151), and steer clear of popular defaults such as 3000 for React, 8080 for backends, and 5432 for PostgreSQL to reduce collisions.
How do I check whether a port is already in use?
On macOS or Linux run lsof -i :PORT or ss -tlnp | grep PORT. On Windows run netstat -ano | findstr :PORT. It is worth verifying locally after generating a port here.
How should I map ports for Docker containers?
Pick any free registered port on the host and keep the application's default port inside the container. For example -p 18080:8080 maps host 18080 to container 8080, which lets you run several copies of the same service at once.