Fonts like any other products need verification to detect and fix errors. We will concentrate our attention on font types widely used with TeX: METAFONT fonts and outline fonts in the PostScript Type 1 format.

A disadvantage is in an individuality of the single glyphs (graphical representations of characters). Despite of their common elements and general font features we usually must check every glyph in all fonts, i.e., in all sizes, in all combinations of possible transformations (bold, slant). Moreover, the bitmap fonts generated from the METAFONT sources should be tested in their visual representation also at various resolutions and magnifications.

The contribution discusses several techniques of verification and comparison. The node and control points, the control vectors and hinting zones are also displayed in proofsheet files generated in PDF (or PS) for a visual verification. Font debugging should be an integral part of a font design. It may be also important to test consistency, compatibility, to detect their violation or other bugs, to show differences between alternatives or releases, etc.

During steps of font processing (conversion, transformation, joining) we could lose compatibility by various reasons. Then a mutual comparison of metric data and glyph shapes between different versions or releases is a good tool to find differences that sometimes may signal inconsistence, incompatibility or even a bug.

The examples are mostly taken from the current TeXLive2005.