> ## Documentation Index
> Fetch the complete documentation index at: https://guide.gpt-trainer.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Introduction

When using [function calling](/rag-from-external-data-provider), you generally need to use publically available APIs - or make your own. However, we also host a number of commonly-used tool functions on our own site, tools.gpt-trainer.com. More are being added every day, so watch this space!

If you would like to suggest a function for us to add, please let us know! You can email us at [hello@gpt-trainer.com](mailto:hello@gpt-trainer.com).

In order to use these tool functions, you must first create your own GPT-trainer API key. For details, please see [Getting a GPT-trainer API Key](/api-reference/api-key-setup).

Our current tool functions are:

<CardGroup cols={2}>
  <Card title="weekday" icon="calendar" href="/tools/weekday">
    Get the day of the week for a given date
  </Card>

  <Card title="Coming soon" icon="question">
    Under construction!
  </Card>
</CardGroup>

## Usage

In each tool function's individual page, the description and parameters of the tool are provided. These can be used directly when creating a function in your agent. For example, the settings in the image below are taken directly from the [Weekday](/tools/weekday) page.

<Frame>
  <img src="https://mintcdn.com/paladinmaxinc/cqqSKD6mznKTkSgB/images/tools-intro-1.png?fit=max&auto=format&n=cqqSKD6mznKTkSgB&q=85&s=71b2d2c27449d3b2ed047343efdef1ce" width="1296" height="1304" data-path="images/tools-intro-1.png" />

  <img src="https://mintcdn.com/paladinmaxinc/cqqSKD6mznKTkSgB/images/tools-intro-2.png?fit=max&auto=format&n=cqqSKD6mznKTkSgB&q=85&s=b0787833b58328da84c5829bbe9c4b55" width="1282" height="1190" data-path="images/tools-intro-2.png" />
</Frame>

For the "Headers" section of the form, you will want to enter the GPT-trainer API key you created earlier, like so:

```json theme={null}
{
  "Authorization": "Bearer Your-GPT-trainer-API-key-here"
}
```

<Warning>
  You must replace *Your-GPT-trainer-API-key-here* with your own API key. The
  tool function will not work otherwise.
</Warning>

And then, just click "Save", and you should be all set!