This looks very good, especially as a teaching tool. Writing and minifying SVG by hand (including path data) is a hobby of mine.

I’m pleased to see that the minification doesn’t put a space after the “0” or “1” of large-arc-flag and sweep-flag; historically I’ve found most minification tools doing so, and even some tools failing to parse `a1 2 3 104 5` (arc: rx=1, ry=2, x-axis-rotation=3, large-arc-flag enabled, sweep-flag disabled, dx=4, dy=5).

One missing optimisation is culling superfluous path commands. If you have two commands of the same type in a row, you don’t need to repeat the letter: `L1 2L-3 4` can become just `L1 2-3 4`; also, after the initial M or m command, it switches to L or l automatically, so in `M1 2L-3 4` the L could be removed.

An area I’d really like to see more work in (in SVG tooling in general) is path simplification/minification. In automated tools I’ve only seen rounding to a fixed number of decimal places, which is what this tool is offering, and which is terrible: some decimal places are far more significant than others, and indeed some points could be happily dropped, and rounding everything is not always the correct behaviour for fidelity. Instead of “two decimal places”, I’d like to see things like “accurate to within one pixel in any given direction”, which I reckon will normally compress better for a given quality level. There’s also the approach taken by Inkscape’s path simplification, which chooses a completely new set of points and curves that approximate the current values, but this harms the accuracy of the path and isn’t flexible enough (you run it in discrete steps, rather than there being a continuous slider or the ability to simplify some sections harder than others, whether automatically for best accuracy or manually).