stringent, demanding, tight, strict, cruel, brutal, exact, unkind, harsh, hard, more...

lenient, lax, easygoing, indulgent, permissive

tough, hard, challenging, arduous, formidable, strenuous, more...

very demanding,   extremely strict,   lacking laxness,   strict or severe,   harsh severe,   really tough,   harsh or severe,   to be strict,   spartan training,   super strict