> For the complete documentation index, see [llms.txt](https://docs.uniot.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.uniot.io/platform/sandbox/visual-editor/special.md).
# Special
Special blocks provide essential control over program execution and event handling. These blocks let you create the main program loop, handle MQTT events, and build event-driven device behaviors.
## task
The main execution loop for your script. This block repeatedly executes the code inside it at a specified interval. Every script requires exactly one task block - it serves as your program's entry point and controls when your device logic runs.
**Parameters:**
* **Iterations** (Number): How many times to run. Set to `0` for infinite execution (most common)
* **Interval** (Number): Time between executions in milliseconds
**Example:**
Read temperature every 5 seconds and send an event with the value
## task pass
Returns the current iteration counter for the task. Useful for creating behaviors that change over time or execute only on specific iterations.
**Returns:**
* **Number**: `-1` for infinite tasks (iterations = 0), otherwise counts down from `n-1` to `0`
{% hint style="warning" %}
This block only works inside a task block. Using it elsewhere will cause an error.
{% endhint %}
**Example:**
Create LED patterns based on iteration
{% hint style="info" %}
Custom iterator implementation using variables to count up instead of down.
{% endhint %}
## is event
Checks whether a specific MQTT event is waiting in the queue. Use this to conditionally process events when they arrive.
**Parameters:**
* **Event Name** (String): The name of the event to check for
**Returns:**
* **Boolean**: `#t` (true) if the event exists in the queue, `()` (false) if not
{% hint style="warning" %}
This block returns true as long as the event remains in the queue. To remove the event, use the **pop event** block.
{% endhint %}
**Example:**
Check and retrieve an event
## pop event
Retrieves and removes the oldest event of the specified type from the queue. Use this to access event data sent via MQTT.
**Parameters:**
* **Event Name** (String): The name of the event to retrieve
**Returns:**
* **Number**: The event payload value, or `()` (empty) if no event exists
{% hint style="warning" %}
Event payloads are always of type **Number**. If you need to send other data types, encode them as numbers.
{% endhint %}
**Example:**
Check and retrieve an event
## push event
Sends an event with a value to the MQTT broker. Use this to publish sensor readings, status updates, or trigger actions on other devices or dashboards.
**Parameters:**
* **Event Name** (String): The name of the event to publish
* **Value** (Number/Boolean): The value to send
{% hint style="warning" %}
Event payloads are always sent as **Number** type. Boolean values are automatically converted: `true` → `1`, `false` → `0`.
{% endhint %}
**Example:**