Today, important political developments can often be decisively influenced with the help of "opinion mining", ie the analysis of the mood or the attitude of the society on certain topics. Therefore, sentiment analysis is more topical than ever. In this master thesis, text analysis tools, which are available to users free of charge and which are available for different Web browsers, are thoroughly investigated. These tools are capable of examining a written input to the effect that the author's feelings, opinions, attitudes or emotions can be categorized and evaluated into a particular "entity". These entities may include, but are not limited to, products, services, organizations, individuals or other subjects that can be judged positive, neutral or negative. Although personal opinions and indirectly communicated messages were no less relevant in the past than they are today, the global advance of the Internet, social media and big data has created a situation where an analysis of the enormous, ever growing data volumes for many companies and organizations have become very important.The following research questions are answered in this master thesis:1. Which free of charge usable Web tools for performing sentiment analyses are currently available?2. How strongly do the tools differ from each other?The functionalities and fields of application of current, free-of-charge and web browser compatible tools, with which sentiment analyses can be carried out, are presented, followed by a comparison of these tools. By means of two case studies, the differences of the tools are explicitly highlighted.