> For the complete documentation index, see [llms.txt](https://devs.truebit.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://devs.truebit.io/developing-truebit-tasks/how-to-create-function-tasks.md).

# How to Create Function Tasks

{% hint style="info" %}
Check the [Supported Languages](/developing-truebit-tasks/how-to-create-function-tasks/supported-languages.md) section to see the specific task preparation steps required for your development language.
{% endhint %}

## Prerequisites

There are several important considerations when writing Function Task code: 

* **Execution environment**: The task must run the same on any computer architecture and operating system. Therefore, Function Tasks execute in an isolated WebAssembly sandbox using our deterministic WASI implementation. Please, check the [WebAssembly ](/developing-truebit-tasks/how-to-create-function-tasks/key-concepts/webassembly.md)section for more information.
* **No network calls:** To provide maximum security, the execution environment does not provide network access. If you need to access data from an external source, consider using an [API Task](/developing-truebit-tasks/how-to-create-api-tasks.md).
* **Determinism**: The execution environment guarantees [determini](/developing-truebit-tasks/how-to-create-function-tasks/key-concepts/determinism.md)[sm](/developing-truebit-tasks/how-to-create-function-tasks/key-concepts/determinism.md) - All Function Tasks will produce the same outputs for given inputs when executed by any Truebit Verify node.

## Building A Function Task 

{% stepper %}
{% step %}

### Write Your Function Task Code

The task developer will create the code, following the best practices described below:

**Replace network operation with filesystem reads and writes**

If your program would normally read and write to network endpoints, you'll need to replace this with filesystem operations.

For example, instead of making an HTTP request to `example.com`,  read from the input.txt file. Click [here](/developing-truebit-tasks/how-to-create-function-tasks/function-task-examples/fibonacci.md#in-out-parameters) to see an example. 

You can write results to the filesystem into an output file. Click [here](/developing-truebit-tasks/how-to-create-function-tasks/function-task-examples/fibonacci.md#in-out-parameters) to see an example.

**Random Numbers**

If your program normally uses random numbers, in Truebit you will always get the same sequence. This is done to ensure a deterministic execution.

**Dates and Times** 

If your program would normally get date-time values, in Truebit you will always get the same value, which is "`1970.1.1 0:1:40`". This is done to ensure a deterministic execution.

**Output value**

The task must return a value. If the result is empty, the task will be marked as failed.
{% endstep %}

{% step %}

### Test Your Function Task

Once your code is ready for testing, the **development workflow involves two primary steps** using the Truebit CLI:

* **Build and Prepare**: Execute the [`build`](/developing-truebit-tasks/truebit-cli-reference.md) command to generate a WebAssembly [(WASM) file](/developing-truebit-tasks/how-to-create-function-tasks/key-concepts/webassembly.md). Truebit utilizes WebAssembly to ensure cross-platform consistency across any hardware or operating system. During this stage, the file is automatically instrumented to guarantee deterministic execution.
* **Execute and Test**: Run the [`start`](/developing-truebit-tasks/truebit-cli-reference.md#start) command to deploy and verify your compiled code within the Truebit environment.

{% hint style="success" %}
Repeat this process every time your source code has been changed.
{% endhint %}
{% endstep %}

{% step %}

### Deploy The Function Task

Once the task is ready for being used by others, the [Task Developer](/overview/how-do-you-intend-to-use-truebit.md#task-developers) will deploy it to make it available for being called by the [Task Requester](/overview/how-do-you-intend-to-use-truebit.md#task-requesters).

#### Authorize The Task execution

The Task Authorization process is an optional step. This step allows the [Task Developer](/overview/how-do-you-intend-to-use-truebit.md#task-developers) to define who has permission to execute the deployed task.

{% hint style="info" %}
Click Here to see more information about the [**Task Authorization**](/developing-truebit-tasks/task-authorization.md) process. 
{% endhint %}
{% endstep %}

{% step %}

### Execute The Function Task

The [Task Requester](/overview/how-do-you-intend-to-use-truebit.md#task-requesters) executes the task using the [Task Execution Endpoint](/integrating-truebit-tasks/api-task-execution.md) from the Truebit API
{% endstep %}
{% endstepper %}

.