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

# Althea REST API Overview

<Info>
  <b>Get an API Key</b>

  Using the Althea API requires an API key.

  You can [sign-up](https://portal.altheastudio.ai) for a free account that comes with 30 free minutes for creating calls.
</Info>

## Base URL

The Althea API is available at `https://app.altheastudio.ai/api/`.

## API Keys

Althea API keys are 41 characters long and are made up of two alphanumeric parts separated by a period. The first part is 8 characters long and the second is 32 characters.

For example: `Zk9Ht7Lm.wX7pN9fM3kLj6tRq2bGhA8yE5cZvD4sT`

Throughout the docs we use `aBCDef.123456` for brevity.

## X-API-Key Header

When making API calls, pass your key in using the `X-API-Key` header.

<Warning>
  <b>You should never expose your API key to client code</b>

  If you *really* want to ignore this advice for a local demo, use the X-Unsafe-API-Key header instead at your own risk. It works the same way except that our server will allow it in CORS preflight requests.
</Warning>

Here's an example showing how to use the fictional API key `aBCDef.123456` to get a list of calls:

<CodeGroup>
  ```bash curl theme={null}
  curl --request GET \
  --url https://app.altheastudio.ai/api/calls \
  --header 'X-API-Key: aBCDef.123456'
  ```

  ```js JavaScript theme={null}
  fetch("https://app.altheastudio.ai/api/calls", {
    method: "GET",
    headers: {
      "X-API-Key": "aBCDef.123456",
    },
  })
    .then((response) => response.json())
    .then((data) => console.log(data))
    .catch((error) => console.error("Error:", error));
  ```
</CodeGroup>

## Rate Limits

The Althea API includes safeguards to help maximize stability for all customers. Too many API requests can trigger an error with status code `429`. See [Scaling & Call Concurrency](/gettingstarted/concurrency) for more information on `429` errors and how to properly handle them.

<APIRateLimits />

### Call Concurrency Limits

The number of concurrent calls allowed depends on your plan.

<ConcurrencyTable />

See [Scaling & Call Concurrency](/gettingstarted/concurrency) for more details on how call concurrency works in Althea Realtime.

## Playground

If you want to quickly experiment with prompts and voices, the fastest way to do that is in the [Althea Dashboard](https://altheastudio.ai/playground).

You can also paste in an Althea API key throughout the API reference (look for "Authorization" and paste your key where it asks for `X-API-Key`) and test the REST API endpoints.