Small features have their own minimums, not just walls
The Minimum Wall Thickness Check on this site covers walls, but holes, slots, embossed text, and thin gaps between separate parts each have their own practical floor relative to your nozzle, and that floor is not identical to a plain wall's. A hole needs to be wide enough for the nozzle to actually trace its circumference without the extrusion overlapping itself closed; embossed text needs a stroke wide enough to read as more than a blob. This tool checks the specific feature type you enter against its own practical minimum, not a single generic number.
How the check works
Each feature type carries its own multiple of your nozzle diameter or assumed line width as a practical minimum: holes need roughly one and a half nozzle diameters to resolve as a clean circle, slots and part-to-part gaps need a bit more than one line width to avoid fusing shut, and embossed text needs roughly two line widths of stroke to read clearly. Your entered feature size is compared against that specific minimum and rated by margin, not treated as pass or fail at a single hard line.
Worked example
A 1.2 mm hole diameter at a 0.4 mm nozzle (roughly 0.6 mm practical minimum): the hole clears with comfortable margin, so the tool returns a low-concern result. Dropping that same hole to 0.5 mm pushes it into the moderate-concern band, close enough to the minimum that a calibration test print is worth running before committing the part.
Limitations
This is a geometric comparison against your nozzle and line-width assumptions, not a simulation of your specific slicer's minimum-feature handling, which can vary between slicers and versions. Confirm any tight-tolerance or cosmetic feature in your slicer's layer preview, and print a calibration piece before committing a full part that depends on it.