Can a Chihuahua eat cookies?
Better to avoid. They may contain sugar, chocolate or xylitol.
How much: If you do, a crumb of a plain cookie with no chocolate or sweeteners.
Why
The problem isn't the cookie itself but what's in it. Chocolate chips, raisins and xylitol are common ingredients.
Cookies in a Chihuahua's diet
Keep in mind how tiny the portions are for this breed: an adult Chihuahua eats roughly 1 to 2.3 ounces (25-65 g) of food a day depending on his weight, and treats shouldn't go over 10% of his daily calories. That's only a small fraction of an ounce. What looks like "a little bite" to us can be half a meal for him.
This information is for general guidance and is not a substitute for advice from a licensed veterinarian. Every Chihuahua can react differently; if in doubt, always check with a professional.