Glossary
Listening port
A network port a process has opened to accept connections, like a dev server on port 3000.
What it is
A server listens on a TCP port so other programs can connect to it. Local development servers usually listen on ports such as 3000, 5173 or 8080.
Only one process can listen on a given port and address. Start a second server on the same port and you get “address already in use”.
Why it matters
Forgotten dev servers keep ports busy and memory in use. Finding which project owns a port is the fastest way to free it.
In Activity Monitor
Double-click a process and open Open Files and Ports. There is no list of listening ports for the whole Mac.
In iKnowMyMac
The Projects screen lists listening ports by project with runtime, uptime, memory and idle time, and flags port conflicts such as “3000 is taken by storefront-web”.
lsof -nP -iTCP -sTCP:LISTENLists every listening TCP port with the owning process and PID.
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