stroke contrast

What's the best software/service for classifying fonts by height, ascender/descender, aperture, etc?

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Is there any font classification service (web page, app, book) that classifies fonts by x-height, ascender and descender lengths, stroke contrast, apertures and counters, besides the basic serif and sans-serif classifications? Also if if the font is made for heading, body, etc.

Stroke contrast in hiragana and katakana

Many Japanese typefaces have areas in which the stroke width reduces to literally nothing in certain areas of certain characters. I don’t have an example handy right this instant, but I can probably come up with some if no one knows what I’m talking about.

Just out of curiosity, can someone explain why this is?