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

# Requirements

> All the requirements for BlackLab WAF

<Info>
  **Prerequisites**:

  * Ruby **2.5 or higher**
  * Rack **1.0 or higher**
</Info>

BlackLab WAF is a **Rack middleware**, which means it plugs into the Ruby web server interface.\
If you are using **Rails**, **Sinatra**, or any other Rack-based framework, you already meet this requirement.

***

## What is Rack?

Rack is a minimal interface between **Ruby web servers** and **Ruby web applications**.\
It provides a consistent API so middleware like **BlackLab** can inspect and filter incoming requests before they reach your app.

For example, in a `config.ru` file:

```ruby theme={null}
require "rack"
require "black_lab"

use BlackLab::Middleware
run MyApp
```

This ensures all HTTP requests go through BlackLab WAF before being handled by your app.

## Supported frameworks

BlackLab works out-of-the-box with any Rack-compatible framework, such as:

* Ruby on Rails
* Sinatra
* Hanami
* Padrino

Or plain Rack apps