MQTT / IoT

Publish messages to and subscribe from MQTT brokers for industrial IoT and Unified Namespace integrations.

The MQTT connector lets your agent exchange data with industrial systems — PLCs, SCADA, MES, and ERP — over the MQTT messaging protocol. Use it to publish commands or readings to a topic, or to receive a single message from a topic as a workflow step.

What you can do

Action	What it does
Publish	Sends a payload to an MQTT topic on your broker.
Subscribe (once)	Waits for one message on a topic and returns its payload to the next workflow node.

Both actions support Quality of Service (QoS) levels and the retain flag. Payloads support {{variable}} template syntax.

The MQTT connector is designed for Unified Namespace (UNS) architectures following the ISA-95 topic hierarchy (enterprise/site/area/line/cell).

Before you start

You need:

A running MQTT broker — for example HiveMQ, EMQX, Mosquitto, AWS IoT Core, or Azure IoT Hub.
The broker's URL (e.g. mqtt://broker.example.com or mqtts://broker.example.com for TLS).
Port — typically 1883 for unencrypted, 8883 for TLS.
Username and password if your broker requires authentication.

For production deployments, enable TLS (mqtts://) and use port 8883. Unencrypted MQTT is only appropriate for isolated local networks.

Connect MQTT

Open your agent in Mojar and go to Integrations in the sidebar.

Find MQTT / IoT in the list of available providers and click Connect.

Fill in the credential form:

Field	Value
Broker URL	Full URL including scheme, e.g. `mqtt://broker.example.com` or `mqtts://broker.example.com`
Port	`1883` (plain) or `8883` (TLS)
Username (optional)	Broker authentication username
Password (optional)	Broker authentication password
Use TLS/SSL	Enable for production brokers; required for `mqtts://`
Client ID (optional)	A unique ID for this connection, e.g. `mojar-workflow-client`

Click Save.

MQTT connector credential form showing Broker URL, Port, Username, Password, and Use TLS fields

Use it in a workflow

Open the workflow editor and add a new node where you want to send or receive an MQTT message.

Select MQTT / IoT as the connector.

Choose Publish or Subscribe (once) as the action.

Set the Topic field. Follow your broker's topic structure. For UNS, use the ISA-95 hierarchy:

acme/plant1/assembly/line2/plc1/temperature

MQTT topic wildcards (+ for a single level, # for multi-level) work for Subscribe only.

For Publish, fill in the remaining fields:

Field	Description
Payload	The message to send. Use JSON for structured data. Supports `{{variables}}`.
QoS	`0` — at most once; `1` — at least once (recommended); `2` — exactly once.
Retain	If enabled, the broker keeps the last message and delivers it to new subscribers.

For Subscribe (once), set a Timeout (default 10 seconds). The node returns the received payload, raw message, and receivedAt timestamp.

Connect the node output to the next workflow step. Published messages return topic, qos, retain, and publishedAt.

For managed brokers (HiveMQ Cloud, EMQX), Mojar automatically uses the broker's HTTP publish API when available. For other brokers, it connects directly via the MQTT protocol.

What you can do

Before you start

Connect MQTT

Use it in a workflow

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