> For the complete documentation index, see [llms.txt](https://px4.gitbook.io/px4-user-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://px4.gitbook.io/px4-user-guide/development/debug/sensor_uorb_topic_debugging.md).

# Sensor/Topic Debugging

The uORB is an asynchronous `publish()` / `subscribe()` messaging API used for inter-thread/inter-process communication. The `listener` command can be used from the *QGroundControl MAVLink Console* to inspect topic (message) values, including the current values published by sensors.

:::tip This is a powerful debugging tool because it can be used even when QGC is connected over a wireless link (e.g. when the vehicle is flying). :::

:::note The `listener` command is also available through the [System Console](/px4-user-guide/development/debug/consoles/system_console.md) and the [MAVLink Shell](/px4-user-guide/development/debug/consoles/mavlink_shell.md). :::

:::tip To check what topics are available at what rate, just use the `uorb top` command. :::

The image below demonstrates *QGroundControl* being used to get the value of the acceleration sensor.

![QGC MAVLink Console](/files/VMoMIU5dg8YKq760AG16)

For more information about how to determine what topics are available and how to call `listener` see: [uORB Messaging > Listing Topics and Listening in](/px4-user-guide/development/middleware/uorb.md#listing-topics-and-listening-in).


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