Parity and Simple Loops (and 5 puzzles)

Before posting the simple loops, I would like to give an introduction to parity, which will be useful for tougher puzzles.

If we consider the grid as a checkerboard, any loop segment will alternate between gray and white cells.

Here are the simple loop puzzles as promised. Most won't require parity deductions.

#227 https://puzz.link/p?simpleloop/9/8/0030h20g3486000

#13 https://puzz.link/p?simpleloop/8/8/240g00200gs00

#63 https://puzz.link/p?simpleloop/13/12/10h0002oc0002000g8c00000g5002100

#120 https://puzz.link/p?simpleloop/21/10/g0g03o80004kggf08000o20203iph0g4a0220109g3

#257 https://puzz.link/p?simpleloop/12/12/1g004g04000000002g000002000h0