Can my dog have nuts?

Avoid

The general rule of the thumb is that dogs should avoid eating nuts, because all of them hold certain toxicity levels. Bearing in mind the huge variety of nuts available, it is hard to keep track of which nuts are dangerous and which are generally safe.

Walnuts are extremely dangerous and should never be used in dogs. The consequences of eating walnuts vary from mild stomach upset to potentially fatal intoxication. Black walnuts contain a toxin named juglon. English and Japanese walnuts are not toxic but lead to stomach upset.
Macadamia nuts and pecans are extremely toxic for dogs even if ingested in small amounts. The toxins found in these nuts are very potent and cause seizures and other neurological conditions.
Almonds, pistachios, cashews and peanuts are not toxic on their own but are hard to digest and can cause mild to severe stomach upset. In addition they are very rich in fats and can easily lead to pancreatitis.
Generally speaking, all nuts are prone to getting molds. If molded, they can contain mycotoxins that cause seizures and have other long-term and life-threatening consequences.
At last, all nuts pose choking hazards especially for smaller dog breeds. Plus, if a whole piece of nut is swallowed without being properly chewed (which dogs tend to do often), it can cause esophageal or intestinal blockage.