Free public test server

Public Relay Server

A free, open Relay instance you can point a client at right now — no sign-up, no API key, no credit card. Use it to try MQTT, MQTT-SN and CoAP over six different transports.

relay.stantialabs.net

Before you connect, read this

This server is open to everyone and requires no authentication. Anyone can subscribe to any topic, including yours.
Never publish private, personal or production data here. Treat everything you send as public.
There is no SLA and no durability guarantee. The server can be reset, upgraded or taken down at any time, and retained messages may disappear with it.
Capacity is shared with every other person testing. Do not use it for load testing or benchmarking — run your own instance for that.

Endpoints

Every listener below is live on relay.stantialabs.net. Ports, transports and connection limits are taken straight from the running configuration.

Protocol	Transport	Port	Address	Encryption	Max connections
MQTT v3.1.1 / v5.0	TCP	1883	mqtt://relay.stantialabs.net:1883	None — plaintext	500,000
MQTT v3.1.1 / v5.0	TLS 1.3	8883	mqtts://relay.stantialabs.net:8883	TLS 1.3	500,000
MQTT v3.1.1 / v5.0	WebSocket	8083	ws://relay.stantialabs.net:8083	None — plaintext	100,000
MQTT v3.1.1 / v5.0	WSS	8084	wss://relay.stantialabs.net:8084	TLS 1.3	200,000
MQTT v3.1.1 / v5.0	QUIC	14567	mqtt-quic://relay.stantialabs.net:14567	TLS 1.3 over QUIC	500,000
MQTT-SN	UDP	1884	udp://relay.stantialabs.net:1884	None — plaintext	10,000
MQTT-SN	DTLS 1.3	8884	dtls://relay.stantialabs.net:8884	DTLS 1.3	10,000
CoAP	UDP	5683	coap://relay.stantialabs.net:5683	None — plaintext	10,000
CoAP	DTLS 1.3	5684	coaps://relay.stantialabs.net:5684	DTLS 1.3 — payloads not yet encrypted	10,000

The TLS, WSS, QUIC and DTLS listeners present a Let’s Encrypt certificate, so your system CA bundle is enough to verify it — no custom trust store needed. If your WebSocket client asks for an explicit path, try /mqtt.

Limits and behaviour

The settings a client will actually notice, as configured on this server.

Authentication	Anonymous — no username or password
Maximum packet size	1 MiB (1,048,576 bytes)
Maximum in-flight messages	32
Handshake timeout	5 s plaintext · 10 s encrypted
Read / send timeout	60 s / 30 s
QUIC idle timeout	120 s
Mutual TLS	Disabled — client certificates are not requested

Connect in a minute

Copy any of these and change the topic. Everything targets the public server as configured above.

mosquitto (TCP)

# Subscribe
mosquitto_sub -h relay.stantialabs.net -p 1883 \
  -t 'relay/demo/#' -q 1 -v

# Publish
mosquitto_pub -h relay.stantialabs.net -p 1883 \
  -t 'relay/demo/hello' -q 1 \
  -m 'hello from mosquitto'

mosquitto (TLS 1.3)

# The server certificate is issued by Let's Encrypt,
# so your system CA bundle is enough.
mosquitto_sub -h relay.stantialabs.net -p 8883 \
  --capath /etc/ssl/certs \
  -t 'relay/demo/#' -q 1 -v

MQTT.js (WSS)

import mqtt from 'mqtt';

const client = mqtt.connect('wss://relay.stantialabs.net:8084/mqtt');

client.on('connect', () => {
  client.subscribe('relay/demo/#', { qos: 1 });
  client.publish('relay/demo/hello', 'hello from the browser');
});

client.on('message', (topic, payload) => {
  console.log(topic, payload.toString());
});

paho-mqtt (Python)

import paho.mqtt.client as mqtt

client = mqtt.Client(protocol=mqtt.MQTTv5)
client.tls_set()  # system CA bundle
client.connect('relay.stantialabs.net', 8883)

client.subscribe('relay/demo/#', qos=1)
client.publish('relay/demo/hello', 'hello from python', qos=1)
client.loop_forever()

CoAP (libcoap)

# GET over plain UDP
coap-client -m get coap://relay.stantialabs.net:5683/relay/demo

# POST a payload
coap-client -m post -e 'hello from coap' \
  coap://relay.stantialabs.net:5683/relay/demo

MQTT-SN (UDP)

# Using the Eclipse Paho MQTT-SN client
paho_mqttsn_sub -h relay.stantialabs.net -p 1884 \
  -t 'relay/demo/#'

paho_mqttsn_pub -h relay.stantialabs.net -p 1884 \
  -t 'relay/demo/hello' \
  -m 'hello from mqtt-sn'

Not enabled on this server

Relay implements these too, but their listeners are switched off on the public instance. The ports below are the defaults you would use on your own deployment.

Protocol	Transport	Default port
STOMP	TCP / TLS	61613 / 61614
AMQP	TCP / TLS	5672 / 5671
NATS	TCP	4222
gRPC	TCP / TLS	9090 / 9091
MCP	WSS	3200
HTTP/3	QUIC	443
WebRTC DataChannel	QUIC	9444

Relay also implements Modbus, OPC UA, DDS/RTPS, SNMP, DNS, A2A, ACP and Agent Mesh, which have no listener configured here. See the full protocol matrix →

Ready for your own instance?

Run the same server in your own cloud on the Free plan — same protocols, same transports, your data, your network.

See pricing Read the docs