SentiStrength is a tool for sentiment analysis available for free to academic users (with registration), in Java and Windows-optimized versions. It estimates the strength of sentiment in short texts, and can handle informal language. Strength is expressed in a scale of 1 to 5 for positive sentiments, and -1 to -5 for negative; it also includes an option for assessing neutrality. SentiStrength is available for multiple languages, with extensibility for languages and contexts not already included. According to the developers, SentiStrength has human-level accuracy for short English texts. Commercial users must purchase a license.