portpeek

Who is occupying my port 3000 / 5173 / 8080?

One command to find the process holding a port — and free it.

No more hunting in Task Manager, no more netstat -ano | findstr.

Keywords: port killer · kill-port · EADDRINUSE · netstat · Windows · Linux · TCP · UDP · CLI

$ portpeek 3000

Port 3000 is in use:

PROTO  PORT  PID  STATE     PROCESS     ADDRESS
-----  ----  ---  --------  ----------  ----------------
TCP    3000  452  LISTENING node.exe    0.0.0.0
TCP    3000  452  LISTENING node.exe    [::]
UDP    3000  452  LISTENING node.exe    0.0.0.0

To free it: portpeek 3000 --kill

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Why

On Windows, this loop is familiar:

1. Local server fails to start
2. Error: listen EADDRINUSE
3. Who has the port?
4. Dig through Task Manager
5. Fight admin / non-admin prompts

portpeek does one job well: show who holds a port, and kick it out.

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vs other port killers

	portpeek	generic kill-port scripts
Shows process name + path	yes	often only PID
Lists TCP + UDP, IPv4 + IPv6	yes	frequently TCP-only
Protects OS processes (lsass, System, …)	yes (--kill skips them)	usually no
Reverse lookup --pid / --name	yes	rare
Free-port picker --free	yes	rare
Zero Python deps	yes	varies
macOS / Linux best-effort	yes	sometimes

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Install

pip install portpeek

Or from source:

git clone https://github.com/jsunnx/portpeek.git
cd portpeek
pip install -e .

Or run without installing:

python -m portpeek

Requires Python 3.9+.

OS	How it reads ports
Windows (primary, tested)	netstat -ano + PowerShell process map
Linux	ss -tulnp + /proc (best-effort, less tested)
macOS	lsof (best-effort, less tested)

If you only care about Windows, it is fully supported. POSIX paths are community-grade.

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Usage

portpeek                     # list LISTEN / bound ports (TCP + UDP, IPv4 + IPv6)
portpeek 3000                # inspect one port
portpeek 3000 5173 8080      # inspect several ports
portpeek --pid 1234          # reverse: which ports does this PID hold?
portpeek --name node         # filter by process name substring
portpeek --free              # print a free TCP port (from 3000)
portpeek --free 8000         # free port starting search at 8000
portpeek --watch 2           # poll until the port state changes
portpeek --sort name         # sort by port | pid | name
portpeek --all               # include non-LISTEN states
portpeek --json              # JSON object with schema_version=1
portpeek --json -o ports.json  # write UTF-8 JSON file
portpeek 3000 5173 --kill    # batch free
portpeek 3000 --kill --force
portpeek 3000 --kill --unsafe  # allow killing protected OS processes
portpeek --no-color          # plain text (CI / pipes)

JSON shape (schema_version is stable for scripts):

{
  "schema_version": 1,
  "count": 2,
  "entries": [
    {"proto": "TCP", "local_addr": "0.0.0.0", "port": 3000, "pid": 452, "state": "LISTENING", "process_name": "node", "exe_path": "..."}
  ]
}

System process protection

--kill never targets critical OS processes by default:

Windows: System (PID 4), Idle, lsass, csrss, smss, wininit, winlogon, services, Registry, Memory Compression, dwm, svchost, spoolsv, …
POSIX: PID 0/1, init, systemd, kernel threads.

If only a protected process holds the port, you get a clear skip message.
Override only with --unsafe (combine with --force if needed) — you can blue-screen or lock yourself out. Don't.

Snapshots are reused for ~0.8s so multi-port / kill paths do not re-run netstat+PowerShell for every call. --kill and --watch force a fresh scan when needed.

JSON / redirect notes (Windows)

• Prefer portpeek --json -o out.json — writes UTF-8 with no BOM.
• PowerShell 5.1 > re-encodes text to UTF-16. For byte-faithful redirect use:

cmd /c "python -m portpeek --json > out.json"
# or
python -m portpeek --json -o out.json

Kill semantics

• Only listening holders are killed (not TIME_WAIT leftovers).
• Windows uses taskkill /T (process tree); --force adds /F.
• After kill, success means the port is no longer listening.
• Access denied → message suggests running as Administrator.

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Common cases

You hit this	Run this
Next / Vite won't start	portpeek 3000
Who owns this PID?	portpeek --pid 4521
Where is node?	portpeek --name node
Need a free port for a script	portpeek --free
Script needs JSON	portpeek 8080 --json
You must use that port	portpeek 8080 --kill

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Design notes

• Zero third-party deps
• Read-only by default: --kill is explicit
• IPv4 + IPv6 kept separate (dual-stack not merged)
• UDP included: Windows UDP rows have no State column
• Portable JSON: ensure_ascii=True
• UTF-8 console on Windows for process names

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Library API

from portpeek import list_ports, find_port, find_by_pid, find_by_name, next_free_port, kill_port

list_ports()
find_port(3000)
find_by_pid(4521)
find_by_name("node")
next_free_port(3000)
kill_port(3000, force=False)

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Tests

python -m unittest discover -s tests -v

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License

MIT

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If this saves you one Task Manager scavenger hunt, a Star is enough. Issues welcome.