---
title: mqtt.publish() function
description: >
  `mqtt.publish()` sends data to an MQTT broker using MQTT protocol.
menu:
  flux_v0_ref:
    name: mqtt.publish
    parent: experimental/mqtt
    identifier: experimental/mqtt/publish
weight: 201
flux/v0/tags: [mqtt]
introduced: 0.133.0
---

<!------------------------------------------------------------------------------

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To make updates to this documentation, update the function comments above the
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------------------------------------------------------------------------------->

`mqtt.publish()` sends data to an MQTT broker using MQTT protocol.



##### Function type signature

```js
(
    broker: string,
    message: string,
    topic: string,
    ?clientid: string,
    ?password: string,
    ?qos: int,
    ?retain: bool,
    ?timeout: duration,
    ?username: string,
) => bool
```

{{% caption %}}
For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
{{% /caption %}}

## Parameters

### broker
({{< req >}})
MQTT broker connection string.



### topic
({{< req >}})
MQTT topic to send data to.



### message
({{< req >}})
Message to send to the MQTT broker.



### qos

MQTT Quality of Service (QoS) level. Values range from `[0-2]`.
Default is `0`.



### retain

MQTT retain flag. Default is `false`.



### clientid

MQTT client ID.



### username

Username to send to the MQTT broker.

Username is only required if the broker requires authentication.
If you provide a username, you must provide a password.

### password

Password to send to the MQTT broker.

Password is only required if the broker requires authentication.
If you provide a password, you must provide a username.

### timeout

MQTT connection timeout. Default is `1s`.




## Examples

- [Send a message to an MQTT endpoint](#send-a-message-to-an-mqtt-endpoint)
- [Send a message to an MQTT endpoint using input data](#send-a-message-to-an-mqtt-endpoint-using-input-data)

### Send a message to an MQTT endpoint

```js
import "experimental/mqtt"

mqtt.publish(
    broker: "tcp://localhost:8883",
    topic: "alerts",
    message: "wake up",
    clientid: "alert-watcher",
    retain: true,
)

```


### Send a message to an MQTT endpoint using input data

```js
import "experimental/mqtt"
import "sampledata"

sampledata.float()
    |> map(
        fn: (r) =>
            ({r with sent:
                    mqtt.publish(
                        broker: "tcp://localhost:8883",
                        topic: "sampledata/${r.id}",
                        message: string(v: r._value),
                        clientid: "sensor-12a4",
                    ),
            }),
    )

```