Find and stop forgotten localhost dev servers on your Mac

Why dev servers get forgotten#

Every web project starts a local server: npm run dev, next dev, vite, rails s, python -m http.server. You open it in a browser, work, and move on. The server often does not move on with you:

• You closed the terminal tab but the server was started with & or nohup.
• It runs inside a VS Code or Cursor window that is minimized on another desktop.
• An AI coding agent started it in a background shell to check its work, and the session ended.

Each one keeps its port, which is why you later hit "port 3000 already in use", and its memory. It also keeps watching your files and rebuilds when they change.

Step 1: list every dev server with one command#

This lists every process you own that is listening on a TCP port:

lsof -nP -iTCP -sTCP:LISTEN -a -u "$USER"

The list includes normal apps too: on our Mac, ControlCenter (AirPlay on ports 5000 and 7000), Notion, the GitHub app and VS Code helpers all listen locally. To see only dev servers, filter by the runtimes that run them. Paste this into Terminal (zsh or bash) to print a clean table with the port, PID, uptime, memory and project folder:

lsof -nP -iTCP -sTCP:LISTEN -a -u "$USER" -c node -c Python -c python -c ruby -c php -c java -c deno -c bun |
awk 'NR>1{n=split($9,a,":"); print a[n], $2}' | sort -un |
while read port pid; do
  printf "%-6s %-7s %-10s %5s MB  %s\n" "$port" "$pid" "$(ps -o etime= -p $pid | xargs)" \
    "$(( $(ps -o rss= -p $pid) / 1024 ))" "$(lsof -a -p $pid -d cwd -Fn | sed -n 's/^n//p')"
done

On our test Mac, with a Next.js site, three small Node servers and a Python server running, it printed:

3000   54115   00:41         28 MB  ~/scratch/demo
3001   54319   00:21        132 MB  ~/DATA/PROJECTS/…/One-Click-Tool-geo
5173   54116   00:41         28 MB  ~/scratch/demo
8000   54118   00:41         11 MB  ~/scratch/demo
8080   54117   00:41         28 MB  ~/scratch/demo

Paths are shortened here; the demo servers ran from a scratch folder. The last column is the folder each server was started in, which is the fastest way to tell which project it belongs to. It ran in about a tenth of a second.

Two details we hit while testing: lsof names the process by its executable, so Next.js shows up as node even though Activity Monitor calls it next-server. And Python from python.org or Homebrew shows up as Python with a capital P, which is why both spellings are in the filter.

Step 2: check how much memory they really hold#

Dev servers are heavier than they look. We loaded two pages of a Next.js 14 site and measured the server:

The drop after a minute is macOS compressing memory that sits unused. The server still owns that memory, and gets it back the moment you save a file and it rebuilds. Three or four forgotten framework servers can easily hold 1–2 GB between them.

Step 3: stop the ones you forgot#

Stop one server with its PID from the table:

kill 54319

kill asks the process to stop normally, the same as Ctrl C. Use kill -9 54319 only if it ignores that.

To stop every Node.js server that is listening on a port, and nothing else:

kill $(lsof -t -nP -iTCP -sTCP:LISTEN -a -u "$USER" -c node)

Add -c Python to include Python servers. On our test Mac, with -c Python added, it stopped all five servers, including the Next.js one and its child process, in about a second; running the list again printed nothing.

Avoid killall node and pkill node. They stop every process with "node" in its name, including editor language servers and helper tools, without showing you what you hit.

If a port still looks busy after this, see port 3000 already in use for single-port checks and the AirPlay case on port 5000.

Prefer a window to a command?#

Activity Monitor shows the same processes if you search for node, with their memory, but it has no column for ports or project folders, so you cannot tell which server is which. That is the gap we built RAM Rescue to fill. Its Localhost tab lists every open port with a health dot, memory and uptime, and a Stop button on each row; a Projects view starts and stops what you build with a live log. The Memory tab also flags dev processes left behind by closed terminals, with a Quit all button. RAM Rescue is free and open source, signed and notarized; see the RAM Rescue page.

Make it a habit#

• Stop a server with Ctrl C before closing its tab.
• Give each project a fixed port in its package.json script, so a clash tells you which project is still running.
• Run the list command at the end of the day, or whenever your Mac starts to feel slow. If the slowness stays, see why kernel_task uses so much CPU.