Microsoft Silverlight is a platform that enables and supports the creation and presentation of interactive elements in browsers and mobile applications. Silverlight is available for different operating systems and devices as a free add-on or plug-in and is used mainly for rich internet applications (RIA) or rich media. Silverlight, which is a Microsoft product, is a competitor to Flash Player – the AIR platform from Adobe.
Microsoft introduced the first version in September 2007.  From the beginning, the tool was designed such that it could be installed on all major browsers and operating systems. Microsoft wanted Silverlight to be a cross-platform tool and, therefore, opted to first restrain from the philosophy of proprietary software and hardware that can only be installed and operated with other in-house products.
The Silverlight plugin is meant to improve the user experience and, in particular, the display of rich media, i.e. media files that contain interactive control elements. At the same time, the focus was on the provision of a platform that would serve as a framework with which developers can create and use interactive contents and elements as well as integrate them in different web applications. Silverlight works therefore in the .NET environment from Microsoft, which provides various programming interfaces. In order to use it as a development framework, the corresponding Silverlight 5 software development kit (SDK) is required.
Silverlight can be used in all common browsers: With add-ons for Internet Explorer, Firefox, Safari, Chrome, and Opera, users can listen to and watch rich internet applications such as diverse video formats in high definition, audio media, animations, and 3D effects. Such rich media are often characterized by two main features: interactive control elements and the fact that a broadband internet connection must be available. On the one side, Silverlight makes it possible to display and play such media. On the other side, it makes it possible to develop rich media within the framework and integrate these in browsers, mobile applications, and different operating systems such as Apple iOS, Microsoft Windows, and Linux. For Linux, however, one must use the Silverlight versions from the Moonlight project that has been set up in the meantime. The main reason for this is presumed to be the fact that newer operating systems from Microsoft rely on HTML5 for the display of interactive content.
In search engine optimization, the integration of rich media content is an important topic with regard to the user experience and accessibility for crawlers and bots. Plugins such as Flash, Shockwave, and Java make it possible to display such content. Since certain content requires special plugins, it may be necessary to use different plugins in order to display diverse content. This in turn benefits the user.
However, many crawlers are unable to read and assign these contents. Therefore, this makes it necessary to give search engines references to the content in the form of meta data.  Here, the first step is the declaration of the data type when integrating Silverlight content. The following is an example of a code for an embedded object:
<object data=“data:application/x-silverlight-5,” style=“display: block” type=“application/x-silverlight-5” >
Other different specifications are also required depending on the type of interactive content. For each individual case, each type or object should be labeled in a way that conforms to the related meta data. This also applies to the use of keywords in the title, description, headings, and text passages. Here, it is very important to ensure that the meta descriptions of the objects used are specified in such a way that enables the different search engine crawlers to identify the type of the content. If Silverlight is used on the entire website, then creating a static page with the active server pages environment (ASP.NET) is recommended in order to ensure that the content can be located by crawlers. When doing this, one should also be careful not to disregard the golden rules of search engine optimization.