MQTT messaged displayed in Event Hub Data Explorer are data_base64

@Mark Pope

Yes, there are ways to display your MQTT messages as JSON in Azure, and alternative components you can use depending on your requirements. Here are few approaches.

Option 1: Decode Base64 in Event Hub Data Explorer (Manual Viewing)

If you simply want to view the payloads as JSON in Azure's Data Explorer:

• The data_base64 field contains your MQTT payload encoded in Base64.
• You can decode it directly using a Kusto query:

EventHubData
| extend decodedPayload = base64_decode_tostring(data_base64)
| project decodedPayload, enqueuedTime, offset, sequenceNumber

This will show the raw JSON if your payload is text-based.

Option 2: Use Azure IoT Hub (Best for MQTT/IoT Workloads)

If you’re working with IoT devices, Azure IoT Hub may be a better fit:

Automatically decodes MQTT messages into readable JSON.

Supports MQTT 3.1.1 and 5.0 natively.

Provides built-in device management (unlike Event Hub).

Allows routing messages to other services (Event Hub, Storage, Functions, etc.).

To switch: Create an IoT Hub and publish MQTT messages to:

devices/{deviceId}/messages/events/

You can then use Azure IoT Explorer or IoT Hub Data Explorer to view messages in JSON format.

Option 3: Use Azure Functions (Automated Conversion)

If you need to keep using Event Hub but want to automate the decoding:

• Create an Azure Function with an Event Hub trigger.
• Decode and forward the payload:

public static async Task Run(
    [EventHubTrigger("my-eventhub")] EventData[] events,
    [EventHub("output-eventhub", Connection = "OutputEventHubConnection")] IAsyncCollector<string> outputEvents,
    ILogger log)
{
    foreach (EventData eventData in events)
    {
        string decodedPayload = Encoding.UTF8.GetString(eventData.Body.ToArray());
        await outputEvents.AddAsync(decodedPayload);
    }
}

This forwards readable JSON to another Event Hub or downstream service.

Option 4: Use Azure Stream Analytics (Real-Time Conversion)

If you need real-time transformation and routing:

• Create a Stream Analytics Job with Event Hub as input.
• Use this query:

SELECT
    System.Timestamp() AS Timestamp,
    CAST(BASE64_DECODE(data_base64) AS NVARCHAR(MAX)) AS JsonPayload
FROM
    YourEventHub

• Output to Power BI, Azure SQL, Blob Storage, or another Event Hub.

If you're working with IoT devices and sending MQTT messages, Azure IoT Hub is likely your best long-term choice since it handles JSON payloads natively and offers more MQTT-specific features. If you're locked into Event Hub, then Azure Functions or Stream Analytics can help you decode and process the data automatically.

I hope this information helps. Please do let us know if you have any further queries.

Kindly consider upvoting the comment if the information provided is helpful. This can assist other community members in resolving similar issues.

Thank you.

Thanks for that! Our customers require mqtt otherwise I would use the IoTHub.

@Mark Pope

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.