Cutting nails during Chol Hamoed?:

One may not cut his nails with a knife or scissor [or nail cutter] during Chol Hamoed. This applies to both the hand and toenails.

For the sake of a Mitzvah: It is permitted to cut nails in their regular way [even with scissors] for the sake of a Mitzvah, such as to immerse in a Mikveh.

One who cut his nails on Erev Yom Tov: One who cut his nails on Erev Yom Tov [or in close proximity to Erev Yom Tov to the point there was nothing to cut before Yom Tov] is permitted to cut his nails during Chol Hamoed.

If one cut his nails a few days before Yom Tov and on Erev Yom Tov there was nothing to cut, may he cut them later on during Chol Hmaoed? Yes.

Those permitted to cut hair: All those who are permitted to cut their hair during Chol Hamoed may likewise cut their nails.

Using one’s finger or teeth: It is only forbidden to cut the nails in their normal way which is by using a vessel, such as a nail cutter or knife. It is however permitted to cut one’s nails using one’s teeth or hands. [Some Poskim even allow slightly cutting the end of each nail using a scissor and to then remove the rest of the nail with one’s hands or teeth.]

May one cut his nails if they are causing him pain? Yes.

May a Mohel cut his nails for purposes of doing a Milah during Chol Hamoed? Yes.

May a woman cut her nails in preparation for Mikvah? Yes.

May a gentile cut one’s nails? Yes.

May one shear his sheep on Chol Hamoed? No.