Grapes are a healthy treat for your chickens as long as they're fed in moderation.

Can Chickens Eat Grapes?

Grapes contain lots of health benefits for humans and for chickens too.  They act as an anti-oxidant and contain nutrients like calcium and potassium. They are also high in Vitamins C and K.

All types of grapes, green, and and black, as well as the grape seeds, can be fed to chickens as an occasional treat without any problems.

Cautions about feeding grapes to chickens. 

But since grapes are high in sugar, they should be fed in moderation. Eating too many grapes is bad for chickens and can lead to digestive issues like diarrhea. 

Grapes can also pose a choking hazard, especially for smaller birds or those who tend to eat fast and gobble up their treats! So I always like to slice or cut the grapes in half or quarters, or squash them and mash them up a bit.

You can feed sort of soft or wrinkled grapes to your chickens, but no moldy or rotten grapes, please.

As an aside, raisins are also okay for chickens to eat (remember they are toxic to dogs and cats though), but again in moderation since they are also very high in sugar.  

As with other treats, in total they should not exceed 10% of your flock's total diet, which equals only about 1 or 2 tablespoons per bird per day.