The package works in the same sort of way as pst-pdf, but it also processes the PostScript graphics with psfrag to add labels within the graphic, before conversion. Thus the bundle replaces two steps of an ordinary workflow. (Naturally, the package requires that \write 18 is enabled.) Pstool ensures that each version of each graphic is compiled once only (the graphic is (re-)compiled only if it has changed since the previous compilation of the document). This drastically speeds up the running of the package in the typical case (though the first run of any document is inevitably just as slow as with any similar package).