How it works
What is read from the file
A font file is a set of tables. The tool reads the table directory, then the name table (family, style, version, designer, copyright, licence), head and hhea (units per em, ascent, descent, line gap, bounding box), OS/2 (cap height, x-height, weight class), post (italic angle), maxp (glyph count) and cmap (which Unicode characters the font covers).
WOFF files are unpacked first; each table is deflate-compressed. For a font collection (.ttc) the first face is read.
Outlines, features and axes
Glyph outlines, OpenType layout features and variable axes are read with opentype.js. Pick any glyph to see its outline drawn in font units on the ascent, cap-height, x-height, baseline and descent lines, with its advance width, left side bearing, bounds and contour count.
The type tester sets your own text in the font. Features from the GSUB and GPOS tables (ligatures, small caps, oldstyle or tabular figures, stylistic sets) switch on and off through CSS font-feature-settings; variable axes such as weight move through font-variation-settings.
size in em = font units ÷ units per em
WOFF2
WOFF2 tables are compressed with Brotli, which this tool does not unpack. A WOFF2 font still loads for the preview, the waterfall and the tester, using the browser's own decoder, and its metric lines are measured from the rendered face; names, tables, the glyph chart and outlines are not shown. Open the TTF or OTF version for the full reading.
