Tomato leaves & stems — Food safety facts
Do not feed · Dogs · full breakdown on the linked food page
The fruit is fine, but the leaves and stems contain solanine and tomatine.
Dogs and cats carry the same rating (Do not feed), so the notes below hold for either pet.
Tomato leaves & stems should not be given to dogs at all. Even a small amount can do harm, so there is no portion small enough to be safe.
Do not induce vomiting and do not give milk or oil to “dilute” it. Note the food and roughly how much was eaten, then call your vet or a pet poison hotline and follow their advice on whether to bring the pet in straight away.
Tomato leaves & stems has no place in everyday feeding: keep the rest of the day's food unchanged after this and watch the next walk and the stool that comes with it.
The full verdict, portion guidance and serving notes are collected on the Tomato leaves & stems food facts page.