Do I need GraphQL, or will REST work?

Both work; GraphQL wins on payload size and tool-response composition. Magento’s REST API often over-fetches, /V1/products/:sku returns ~40 fields when you only need 3. That’s wasted network bytes and wasted LLM tokens (the model has to ignore the noise). GraphQL lets you ask for exactly the fields the tool needs, typically trimming the payload 30-50%. Where REST still wins: (a) write operations (GraphQL’s mutations are uneven across Magento entities; REST is more complete); (b) stock and inventory (the V1 stockItems endpoint is the simplest path); (c) admin-only endpoints not exposed in GraphQL. Use GraphQL for catalogue + orders + customers; use REST for inventory + admin writes. Both clients hang off the same authenticated httpx session.