This paper describes an availability analysis tool that is developed to simulate a ground-based augmentation system (GBAS) prototype as an integrity monitoring test-bed (IMT) at an airport of interest. This simulation tool includes the IMT master station algorithm, reference station algorithm, reference station siting configurations, and IMT user algorithm. In addition, a user-friendly graphical user interface is developed to allow the user to modify the parameters of the algorithms, the IMT reference station network, user locations, and satellite constellations. The output of the tool is the Stanford Chart, which indicates the availability for the user protection level calculation versus various required navigation performance levels, such as Category I landing. The simulation tool is implemented in Qt (http://qt.digia.com/), an open-source cross-platform toolkit, allowing the tool to run on various devices. Several airports in different flight information regions are used as examples to demonstrate the utility of the proposed IMT algorithm and the configuration availability simulation tool by analyzing their GBAS service volumes. Cases with reduced error models are also simulated in this paper. This study develops a fast, accurate, and highly customizable GBAS availability simulation tool for GBAS algorithms and configuration planning at the airport of interest.