Tomato — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Ripe red fruit is fine in small pieces. Green parts (leaves, stem, unripe fruit) contain solanine, which is toxic.
Short answer
Yes, green tomatoes and tomato leaves are toxic to dogs. They contain solanine, a compound that can cause vomiting, diarrhea, and weakness. Stick to small amounts of fully ripe red flesh only. If your dog ate green parts, call your vet or the ASPCA poison hotline at 888-426-4435.