<p>Informal science settings, such as zoos, aquariums, and science centers, naturally spark emotions ranging from curiosity and excitement to frustration. Yet, studying emotional experiences in informal science learning (ISL) environments has been difficult, largely due to the challenges of measuring emotions in real time. Traditional methods, including self-reports, physiological measures, and observational approaches, offer useful insights but also come with their own limitations. To address these, the aim of this study was to develop an observational tool to systematically document observable emotional expressions during ISL visit - the EMOTool (Emotions Observational Tool), specifically designed for researchers conducting observational studies in ISL environments. The EMOTool utilizes observational data from eight studies in ISL settings to develop a comprehensive taxonomy of emotions observed in these contexts, incorporating refined definitions that include observable behaviors and discursive markers, along with an adapted version of the Affect Grid for accurate emotion coding. The EMOTool provides ISL researchers with a practical tool for emotion research and analysis, improving clarity and precision in identifying and distinguishing emotions within observational data. We expect that the EMOTool will enhance research in ISL contexts, providing the means to identify emotions in real-time and serving as a crucial step towards deeper understanding of the role of the emotional experiences.</p>