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

# Introduction

> ECSEND Developer API Documentation

## Welcome

Welcome to the ECSEND Developer API. This API allows you to programmatically:

* Send SMS messages
* Manage contacts and address books
* Create and manage SMS campaigns
* Check your account balance

## Authentication

All API endpoints are authenticated using an API Key via the `X-Api-Key` header.

```bash theme={null}
X-Api-Key: your_api_key_here
```

<Card title="View OpenAPI Specification" icon="file-code" href="/openapi.yaml">
  Download the OpenAPI Specification file
</Card>