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

# Introduction

> General concepts, response codes, and authentication strategies for the Bigcapital API.

<Note>
  This section introduces the Bigcapital API, including authentication, response
  codes, and rate limits.
</Note>

## Base URL

The Bigcapital API is built on **REST** principles. We enforce **HTTPS** in every request to improve data security, integrity, and privacy. The API does not support **HTTP**.

All requests contain the following base URL:

```
https://api.bigcapital.com
```

## Authentication

To authenticate, add an *Authorization* header with the contents of the header being `Bearer bc_xxxxxxxxx` where `bc_xxxxxxxxx` is your API Key.

```
Authorization: Bearer bc_xxxxxxxxx
```

## Response codes

Bigcapital uses standard HTTP codes to indicate the success or failure of your requests.

| Status | Description                                 |
| ------ | ------------------------------------------- |
| 200    | Successful request.                         |
| 400    | Check that the parameters were correct.     |
| 401    | The API key used was missing.               |
| 403    | The API key used was invalid.               |
| 404    | The resource was not found.                 |
| 429    | The rate limit was exceeded.                |
| 5xx    | Indicates an error with Bigcapital servers. |

## Rate limit

The default maximum rate limit is **2 requests per second**. This number can be increased for trusted senders by request. After that, you'll hit the rate limit and receive a `429` response error code.