> ## Documentation Index
> Fetch the complete documentation index at: https://guides.robylon.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Create & Use APIs, Tools, and Functions

> Learn what APIs, Tools, and Functions are, when to use them, and how to implement them effectively with reusable templates, contracts, and Python code.

Use **APIs**, **Tools**, and **Functions** for advanced customization and integrations.

* **APIs** connect external systems and fetch/update data.
* **Tools** package repeatable actions behind clean input/output contracts.
* **Functions** run **Python** for custom logic that blocks can’t express.

***

## APIs

### What is an API?

An **API template** defines how to call an external service (method, URL, headers, params/body) and where to store the response for use in workflows.

**Best practices**

* Centralize repeated calls as **saved templates**.
* Use **secrets** for authentication (`${secrets.*}`).
* Reference workflow variables (`${vars.*}`) for dynamic values.
* Normalize responses and save them into `vars.*`.

***

### How to Create an API Template

<Steps>
  <Step title="Navigate to APIs">
    Go to the **APIs** section in the sidebar.
  </Step>

  <Step title="Add a New API">
    Click **Add API** to create a new template.
  </Step>

  <Step title="Configure the API Call">
    Define:

    * **Name** — e.g., `get_order_status`
    * **Request** — method (**GET**, **POST**) and URL
    * **Headers** — use secrets for auth tokens
    * **Params / Body** — JSON or key-value format
    * **Response Mapping** — select a variable to store results
  </Step>

  <Step title="Save the Template">
    Click **Save**. The API is now reusable across workflows.
  </Step>
</Steps>

## Tools

### What is a Tool?

A Tool is a reusable action that can be called by workflows or AI agents. Tools are best when multiple flows need the same logic with consistent inputs and outputs.

### Best practices

* Convert tested workflow logic with Pre-convert Tool.
* Keep tools stateless and idempotent.
* Define clear input/output contracts.
* Add a consistent error shape (code, message).

### How to Create a Tool

* Design logic in a workflow.
* Use Pre-convert Tool to save it as a reusable action.
* The Tool appears in the Tools section with inputs and outputs inferred.

## Functions

### What is a Function?

A Function is a block of Python code used when other workflow blocks aren’t flexible enough. Functions can validate data, run calculations, or transform values.

### Best practices

* Keep functions small, pure, and testable.
* Validate inputs early.
* Use them for transforms, calculations, and glue code.
* Avoid long scripts or network I/O (better suited to APIs/Tools).

## Testing & Troubleshooting

* Dry-run APIs with sample variables; inspect responses.
* Add internal logs for APIs, Tools, and Functions.
* Use standard error shapes for consistency.
* Keep functions lightweight; make tools reusable.
* Prefer idempotent operations for safe retries.