Port Number Lookup

Look up what port numbers such as 22, 443, and 3306 are used for, by number, service name, or word. Lists more than 120 common ports with an explanation and covers every number in the IANA registry. Also shows which ports browsers refuse to open and reads the ports in netstat, ss, or lsof output. Runs entirely in your browser.

How to use

In "Search by number, service name, or word", type the port number you want to look up (3306), a service name (ssh), or a word for what it does (mail, database)
The matching ports appear in numeric order. Each shows the kind of range it falls in (system port and so on), what it is commonly used for, and its entries in the IANA registry
Choose a category such as Databases under "Category of common ports" to see only the common ports in it
To check the ports in use on a server all at once, paste the output of netstat or ss into "Look up the ports in command output" below

There is no button to press. The results change as you type. When the page opens, the common ports (more than 120) are listed in numeric order.

Searching

Number — Typing 443 shows that port alone. A number with nothing registered still shows its range and any warnings. The forms :8080 and 53/udp and full-width digits are read too
Range — 8000-8100 lists the commonly used and IANA-registered ports in that range. 8000〜8100 and 8000 - 8100 work too
Service name — ssh, postgresql, mqtt, and so on, including the names in the IANA registry
Words — The common ports can be found by words in their explanation (mail, remote), by category name (databases), and by product names (Tomcat, Grafana, Minecraft). The IANA registry is in English, so it is searched with English words (database, printer)
TCP and UDP — Typing tcp or udp keeps the ports used over that transport. Combine it with other terms, as in dns udp or 443 tcp
More than one — Separated by spaces, any of the numbers and ranges may match, and every word must. 8000-9000 http lists the HTTP-related ports from 8000 to 9000

A wide range can match a great many ports. Up to 50 are shown at once, lowest first, along with how many matched in all.

Looking up the ports in command output

Run one of these commands on a server or computer and paste the output as it is.

Linux: ss -tulpn or netstat -tulpn
macOS: lsof -i -P -n or netstat -an
Windows: netstat -ano
Docker: docker ps

Port numbers in the forms 127.0.0.1:5432, [::]:22, *.5432 (macOS netstat), and 0.0.0.0:8080->80/tcp (docker ps) are read and listed in numeric order. Ports found on listening lines (LISTEN, LISTENING) are marked "Listening". Press "Look up …" next to a port to search for it in the field above.

Without -P, lsof shows service names such as http instead of numbers. Ports shown by name cannot be read, so run it with -P. Port 0, which means "any port", is left out.

Example

Typing 5000 shows the following.

5000  User port (1024–49151)
      Flask / AirPlay Receiver  TCP
      The default port of the Flask development server. On macOS Monterey and later, AirPlay Receiver listens on ports 5000 and 7000, …
      A convention rather than an IANA registration.
      IANA registry
      commplex-main (TCP/UDP)

When a development server on a Mac will not start on port 5000 or returns 403, AirPlay Receiver may be the cause.

A number inside a range registered as a block, such as 6010, shows the range entry, as in x11 (TCP/UDP, registered for 6000–6063) X Window System.

Suppose part of the output of ss -tuna (which shows both listening and connected sockets) reads as follows.

tcp   LISTEN 0  128     0.0.0.0:22     0.0.0.0:*
tcp   LISTEN 0  4096  127.0.0.1:5432   0.0.0.0:*
tcp   ESTAB  0  0     10.0.0.2:50000   1.1.1.1:443

Pasting it lists four ports: 22 (SSH, listening), 443 (HTTPS), 5432 (PostgreSQL, listening), and 50000 (dynamic port). Port 50000 is most likely the source port the operating system picked for an outgoing connection.

The three ranges of port numbers

Port numbers run from 0 to 65535, and RFC 6335 divides them into three ranges.

System ports (0–1023) — Also called well-known ports. They are assigned to long-established services such as HTTP (80) and SSH (22). On Linux, listening on these ports needs administrator rights (root or CAP_NET_BIND_SERVICE)
User ports (1024–49151) — Also called registered ports. Services that applied to IANA, such as MySQL (3306) and PostgreSQL (5432), use them
Dynamic ports (49152–65535) — Also called private or ephemeral ports. IANA assigns nothing here; operating systems use them freely for connections, and organizations may use them internally

Source ports (ephemeral ports)

For an outgoing connection, the operating system picks the source port on its own. By default, Linux picks from 32768–60999, and Windows and macOS from 49152–65535. A server listening on a port in this range can fail to start because the port happens to be in use as a source port, so the results warn about it.

Ports browsers refuse to open

Browsers do not connect to certain ports for http:// and https:// URLs. This stops web pages from sending data that looks like real requests to servers for other protocols, such as mail or FTP. The ports are listed as "bad ports" in the Fetch Standard (WHATWG), which the major browsers follow.

There are 83 of them, including 22 (SSH), 25 (SMTP), 587 (mail submission), 6000 (X11), 6665–6669 (IRC), and 10080. A development server on one of these ports cannot be opened in a browser: http://localhost:6000 gives an error such as ERR_UNSAFE_PORT in Chrome. The app points this out for each such port.

What the lists contain

Common ports — More than 120 ports, each with an explanation in Japanese and English, the transport it uses (TCP or UDP), and a category. Ports used by convention for something other than their IANA registration, such as 3000 for development servers and 1521 for Oracle Database, are marked as conventions
IANA registry — The IANA "Service Name and Transport Protocol Port Number Registry" as retrieved on October 18, 2026, including registrations up to October 15, 2026. Registrations for TCP, UDP, SCTP, and DCCP are shown together for each port. Registrations listed without a transport, such as vrml-multi-use for 4200–4299 and reserved ports, are included. Rows that only say "Unassigned" are left out, so a port with no registration shows "Not in the IANA registry"
Ports browsers refuse to open — The Fetch Standard list as of October 18, 2026

An IANA registration is neither permission to use the port nor a promise that whatever listens on it is the registered service. Use the commands above to check what is actually listening.

FAQ

What is a port number?

A number that tells which program on a computer a connection is for. If the IP address is the address of a building, the port number is the room number. Web servers listen on ports 80 and 443, mail servers on port 25, and so on, each service on its own number.

Is the same number over TCP and UDP the same thing?

No. TCP port 53 and UDP port 53 are separate endpoints in the operating system. IANA often assigns both to a service at once, though, so the registry frequently shows the same name for both. The common ports in this app show the transport that is actually in common use.

Can I use 3000 or 8080 for anything?

On your own machine or within your organization, any number works. If it clashes with other software, though, one of them cannot start, so it is safer to avoid busy numbers or to make the port easy to change. For a web server, pick a port that is not among the ports browsers refuse to open.

What should I do when it says the port is already in use?

Another program is already listening on that port. On Linux, ss -tulpn shows which program it is; on macOS, lsof -i -P -n | grep LISTEN; on Windows, netstat -ano. Paste the output into this app to see what each port is commonly used for.

Which ports should I open in a firewall?

Only the ones for the services you use: 80 and 443 for a web server, 22 for SSH. Databases (3306, 5432, 6379, 27017, and others), file sharing (445), Remote Desktop (3389), and the Docker API (2375) are frequent targets, so as a rule they should not be exposed to the internet directly.

Does a port missing from the registry mean nobody uses it?

It only means IANA has no registration for it; some software may still use it. Conversely, many registered ports are hardly used today.

Can I read the explanations in Japanese?

The Japanese page shows the same lists with explanations in Japanese. The IANA registry descriptions stay in English on both pages.

Is anything I type sent anywhere?

No. Both the search and the reading of pasted command output happen in your browser. The IANA registry is bundled with the app, and no outside server is contacted.

Type: Utility
Category: Developer
Tags: port; tcp; udp; network; firewall; reference; developer

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Look up the ports in command output