This package provides macros for measuring alphabet lengths (i.e. the length occupied by the characters “abcd…xyz”), em-widths and ex-heights, which may help in making typesetting decisions. The package is compatible with pdfLaTeX, LuaLaTeX, and XeLaTeX, and will accept font family switches defined via the fontspec package. The plan is that future versions shall be able to provide even more diagnostic tools, and some LuaTeX-specific special commands, too. The package relies on the following other LaTeX packages: expl3, array, booktabs, and siunitx.