LANList: A Minimal Local Device Presence Map (mDNS + Tiny Web UI)

Alex Solis ·Nov 20, 2025

What and why

LANList is a tiny, local-only presence map for your home or workshop network. It discovers devices that advertise via mDNS/Bonjour, aggregates their names, IPs and service types, and serves a tiny static web page you can open on any device on the LAN. It's deliberately minimal: low CPU and memory, no third-party services, no accounts, and a small codebase you can read in one sitting.

What you need

A small always-on Linux host. Raspberry Pi Zero W is perfect, but any Pi, an old laptop, or a tiny VM works.
Python 3.8+ (usually preinstalled) and pip.
Network access to the devices you want to see — mDNS only works on the same link unless your router forwards it.

Install (fast path)

Update your Pi and install dependencies: sudo apt update && sudo apt upgrade -y
Install pip packages: python3 -m pip install --user zeroconf flask
Create a project folder: mkdir -p ~/lanlist && cd ~/lanlist

Minimal code

This is intentionally tiny. Create a file lanlist.py with the following contents:

from zeroconf import ServiceBrowser, Zeroconf
from flask import Flask, jsonify, render_template_string
import threading

services = {}

class Listener:
    def remove_service(self, zc, type_, name):
        services.pop(name, None)
    def add_service(self, zc, type_, name):
        info = zc.get_service_info(type_, name)
        if info:
            ips = ["%d.%d.%d.%d" % tuple(b) for b in info.addresses]
            services[name] = {
                'name': name,
                'type': type_,
                'ips': ips,
                'port': info.port,
            }

zc = Zeroconf()
listener = Listener()
ServiceBrowser(zc, "_services._dns-sd._udp.local.", listener)

app = Flask(__name__)

TEMPLATE = '''LANList


LANList — local devices
{% for s in services %}{{s['name']}} — {{s['type']}} — {{', '.join(s['ips'])}} :{{s['port']}}
{% endfor %}
Updated live from mDNS. No external calls.'''

@app.route('/')
def index():
    return render_template_string(TEMPLATE, services=sorted(services.values(), key=lambda s: s['name']))

@app.route('/json')
def api():
    return jsonify(sorted(services.values(), key=lambda s: s['name']))

if __name__ == '__main__':
    # Run Flask in a background thread to keep zeroconf running in main thread
    threading.Thread(target=lambda: app.run(host='0.0.0.0', port=8080), daemon=True).start()
    try:
        input('LANList running. Press Enter to stop.\n')
    finally:
        zc.close()

Save it and run with: python3 ~/lanlist/lanlist.py. Point a browser to http://your-pi-ip:8080/ and you should see a simple list of discovered devices.

How it works (brief)

zeroconf library listens for mDNS updates and keeps a dictionary of services.
Flask serves a minimal UI and a JSON endpoint. The UI is static and rendered on request — no JS required.
All discovery and serving stay local to your LAN.

Deploy as a service

Create a systemd unit /etc/systemd/system/lanlist.service with: [Unit] Description=LANList After=network-online.target [Service] User=pi WorkingDirectory=/home/pi/lanlist ExecStart=/usr/bin/python3 /home/pi/lanlist/lanlist.py Restart=on-failure [Install] WantedBy=multi-user.target
Enable and start: sudo systemctl daemon-reload && sudo systemctl enable --now lanlist

Troubleshooting

If nothing appears, confirm that devices actually advertise mDNS. Many IoT devices do; others (some printers, routers) may not.
Check network isolation features on your router. Guest networks often block mDNS.
Run python3 -c 'from zeroconf import Zeroconf; z=Zeroconf(); print(z.get_addresses())' to ensure zeroconf initializes without error.
If you see only IPv6 addresses or empty address lists, your devices might prefer IPv6 or the Pi has IPv6-only configured. Adjust the code to handle IPv6 if needed.

Small enhancements (pick one)

Add a tiny heartbeat: poll a few IPs with ICMP to show online/offline status.
Cache results to disk every minute so a reboot doesn't leave you empty-handed for a bit.
Serve a compact favicon and tiny CSS from the same app for a cleaner UI.

Privacy and limits

LANList deliberately keeps data local. It does not phone home, log to cloud services, or require accounts. But be mindful: the dashboard shows device hostnames and IPs visible on your LAN — treat it like any other internal inventory. If you expose this port beyond your LAN (don't), you leak that inventory.

Tip: Use a firewall or router rule to restrict access to the Pi's 8080 port if you need tighter control.

Closing

LANList is designed to be simple and useful. It's not a full network scanner or home assistant replacement — it's a small, transparent tool that gives a quick answer to the question: what's advertising itself on my LAN right now? You can extend it as you like, but starting with a tiny, readable codebase keeps things debuggable and privacy-friendly.

If you build something neat on top of this — a tension-free upgrade path is to add tiny icons, group devices by vendor, or push a local notification when a specific device arrives — drop a note in your project log and keep the stack minimal.