Port conflicts on Mac

Your dev server won’t start because something else already has its port. These guides cover the commands that find and free it on macOS, and the traps in the one-liners everyone copies.

• How to kill a process on a port on MacFind what’s listening, stop it politely, and only force it if you must.
• Port 3000 is already in useWhat usually holds 3000, and how to free it without killing your browser.
• EADDRINUSE: address already in useWhat the error means in Node, Python and Rails, and the fix.
• lsof for ports on macOSThe flags that make lsof readable, and why you need -sTCP:LISTEN.