rack-metadata 
Inject meta tags into your head. This rack middleware collects meta data about a page and will inject meta tags into the head of your html content.
Usage
# in your rack up/config file
use Rack::Metadata
# in your application
env['rack.metadata'] = {
description: "My page's meta description",
keywords: "Foo, bar"
}
It the request is text/html, the middleware will add meta tags for description and keywords:
<head>
…
<meta name="description" content="My page's meta description" />
<meta name="keywords" content="Foo, bar" />
…
</head>
All other content types are currently ignored.