Public MQTT sandbox

A free public MQTT broker for client testing

Validate a client, teach publish and subscribe, or reproduce a protocol issue without provisioning infrastructure. The shared endpoint has no SLA and must never carry secrets or production telemetry.

Follow the MQTT tutorial Compare managed cloud plans

Connection profile

Connect to the shared endpoint

Use a unique client ID and keep the shared username and password in environment variables so rotation does not require code changes.

Public broker profile

Hostpublic.runmqtt.com

TCP1883

TLS8883

Usernameajbkvbp/demo

PasswordOCDWjjOSlSexcWRG

Client IDrunmqtt-test-<unique-id>

Shared access details rotate. Copy the current username and password into MQTT_USERNAME and MQTT_PASSWORD before running the examples.

Mosquitto CLI over TLS

# Load the current credentials shown on this page
export MQTT_USERNAME="ajbkvbp/demo"
export MQTT_PASSWORD="OCDWjjOSlSexcWRG"

# Subscribe
mosquitto_sub \
  -h public.runmqtt.com -p 8883 \
  -u "$MQTT_USERNAME" -P "$MQTT_PASSWORD" \
  -i "runmqtt-sub-$(date +%s)" \
  -t "sandbox/$USER/telemetry" -q 1

# Publish from another terminal
mosquitto_pub \
  -h public.runmqtt.com -p 8883 \
  -u "$MQTT_USERNAME" -P "$MQTT_PASSWORD" \
  -i "runmqtt-pub-$(date +%s)" \
  -t "sandbox/$USER/telemetry" -q 1 \
  -m '{"temperature":22.4,"unit":"C"}'

Sandbox rules

Design the test around shared-broker limits

A public broker is useful precisely because it is disposable. Treat every session, retained message, and credential as temporary.

Shared capacity

Other testers share connections and throughput. Expect throttling or resets during noisy periods.

Ephemeral state

Do not depend on retained messages, persistent sessions, or long-lived subscriptions surviving cleanup.

Rotating access

Shared access can change without notice. Keep connection details outside source code.

No sensitive data

Topic names and payloads may be visible to other users. Publish synthetic data only.

When to upgrade

Use the sandbox to learn; use a managed cloud broker to operate

Broker capability
Broker capability	Public sandbox	Managed broker
Identity	Shared, rotating credentials	Scoped device credentials
Topic access	Shared namespace for disposable tests	Reusable publish and subscribe policies
Operations	Best effort with no lifecycle guarantees	Owned runtime, health, and billing state
Data	Synthetic payloads only	Private application workloads

Move when clients require a stable endpoint and credentials.

Move before using customer, device, or operational data.

Move when devices need different publish and subscribe rights.

Move when a demo becomes a repeatable integration or service.

Public MQTT broker FAQ

Can I send production traffic through the public broker?

No. The endpoint is shared, best effort, and may reset sessions or rotate access details. Use it for client validation, workshops, and short-lived demos only.

Should I use port 1883 or 8883?

Prefer 8883 with certificate validation. Port 1883 is useful only for isolated troubleshooting because payloads and credentials are not encrypted in transit.

Why can shared credentials change?

Rotation limits abuse and clears stale workshop access. Keep credentials in environment variables and check this page before a scheduled test.

Why does my client disconnect as soon as another client connects?

MQTT brokers allow one active session per client ID. Generate a unique client ID for every browser tab, process, device, and workshop participant.

Take the next step

Learn the protocol, harden the connection, then choose the operating model that fits your workload.