XSPEC is a command-driven, interactive, X-ray spectral-fitting program, designed to be completely detector-independent so that it can be used for any spectrometer. All of Swift's spectral data can be used in XSPEC. XSPEC is distributed as part of the HEAsoft software package. Extensive help with XSPEC is available simply by typing help at the XSPEC prompt and following the instructions.
WEBSPEC is a Web tool based on XSPEC. WEBSPEC implements a subset of the functionalities of XSPEC. It allow easy access and use without the need to install software, but WEBSPEC does not have all the functionality of XSPEC. An example of using using XSPEC to simulate GRB spectra, and using UVOT data in XSPEC, is available at the SSC proposers Web page. Please note that the response matrices provided there may not be the most up-to-date versions and care should be taken when using them to simulate spectra. The most up-to-date response matrices can be obtained from the Swift CALDB.