Direct answer
Every Shopify store already serves an /llms.txt: since May 28, 2026, Shopify generates a managed /agents.md and serves the same content at /llms.txt and /llms-full.txt. That default tells AI agents how to browse and buy (store endpoints, product and search URLs, policies) rather than describing your catalog. If you want a buyer-facing map of your homepage, priority collections, key products, FAQ, shipping, returns and buying guides instead, draft it here and publish it by adding an llms.txt.liquid template to your theme.