Want to know how to show the preview of a link to your webpage on slack?
Slack uses meta tags on your webpage to display previews, just like twitter/face book does. So all you need for slack to show the preview of your web page is to set the following meta tags in your page header.
<head> <meta property="og:title" content="Title of your page. This will also be the title of the slack preview"/> <meta property="og:description" content="Description of your page. Slack shows this as the description in it's preview"/> <meta property="og:image" content="/images/og/default.jpg"/> <!-- This image will be shown on the slack preview as well --> </head>
This is by no means an exhaustive list of tags that you can use. In fact there are a lot more tags that can be added. They are described in detail in the refernce links.