Checking a Font

The Compare section in the grid view puts every master against the active one.

What Compare reports

Glyph count	A master missing glyphs the others have.
Structural incompatibilities	Glyphs that cannot interpolate, listed rather than discovered one at a time.
Differing advances	Widths that disagree where they should not.
Kerning pairs	The count per master, which catches kerning that only got done once.
Vertical metrics	Values that disagree between masters.

The Dimensions section measures stems and bars from the reference glyphs in each master. The numbers are measured from the outlines, not typed in, so they say what you drew rather than what you meant.

Use it to check that a designspace’s weights step evenly, and to check the Stems values in Font Info against reality.

The Curves section draws a curvature comb and a continuity display over the glyph. A kink that is invisible at text size shows as a break in the comb.

Harmonize, Balance, and Fit Curve are the usual repairs. See Paths and Filters.

Before export

Correct Path Direction	Outer contours one way, holes the other.
Tidy Up Paths	Zero-length segments, which are invisible and break interpolation.
Round Coordinates	Whole units, if that is your convention.
Bake Masks	Makes mask subtraction real, so the exported outline matches the preview.

Glyph → Check Joining measures the connecting stroke’s band at the joining edges of every positional form, finds the font’s common band, and selects every form that misses it.

A form that misses the band is what makes a script nearly join. See Text and Shaping.

The measure tool colours the outline by thickness, labels handle and segment lengths, and measures stems, counters, and sidebearings. Turn on what you need in the Measure section while the tool is active. See Tools.

Then read it. Switch to the text tool, type words in the scripts the font is for, and look at them at size. When something comes out wrong, the Shaping section shows which characters produced which glyphs.