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

# Authentication

> The AgentTest backend uses API keys to authenticate requests. All API endpoints are protected and require a valid API key to be included in your requests.

## Using the API Key

To authenticate your API calls, you must include an `x-api-key` header with your secret API key.

**Example using cURL:**

```bash theme={null}
curl -X POST \
  -H "Content-Type: application/json" \
  -H "x-api-key: YOUR_SUPER_SECRET_API_KEY" \
  -d '{ "userId": "user-test-123" }' \
  https://your-agenttest-backend.example.com/experiment/my-prompt-test/assign
```

Replace `YOUR_SUPER_SECRET_API_KEY` with the actual API key you've configured for your backend instance, and `https://your-agenttest-backend.example.com` with the URL of your deployed AgentTest backend.

## Setting up the API Key

The API key is defined in the `.env` file in the root of your AgentTest backend project. You need to set the `API_KEY` variable:

```env theme={null}
# .env file
DATABASE_URL="your_supabase_connection_string"
API_KEY="your_super_secret_api_key_here"
# Other variables like PORT can also be here
# PORT=3001
```

* Choose a strong, unique string for your API key.
* This `API_KEY` value is what the backend server will expect in the `x-api-key` header.

<Warning>
  **Keep your API key secure!**
  Your API key grants access to your AgentTest backend, including assigning variants and logging results.
  Do not expose it in client-side browser code or commit it to your version control system if the `.env` file is not gitignored (by default, `.env` files should be in `.gitignore`).
  Treat it like a password.
</Warning>

## Unauthenticated Requests

If an API request is made without an `x-api-key` header, or if the provided key is invalid, the server will respond with a `401 Unauthorized` HTTP status code.

```json theme={null}
{
  "error": "Unauthorized"
}
```