--- title: "Core commerce modules" description: "Learn how Mercur builds on Medusa’s core commerce modules" --- # Core commerce modules Mercur is built on top of **Medusa’s core commerce modules**.\ These modules provide the foundational commerce primitives used in every Mercur marketplace: products, pricing, carts, orders, customers, payments, fulfillment, inventory, and more. Mercur does **not replace** these modules.\ Instead, it creates additional marketplace domain logic - such as sellers, commissions, order splitting, payouts, requests, reviews, and vendor-level operations. Below is an overview of every Medusa core module, along with a short description and a reference link to the official Medusa documentation where you can learn more about each module. --- Handles API key management and authentication for programmatic access. Provides authentication flows, hashing utilities, and identity management. Manages carts, line items, promotions, and total calculations. Used by Mercur for multi-vendor cart orchestration. Defines currencies and formatting rules. Stores customer profiles, addresses, and preferences. Handles fulfillment providers and shipping. Mercur extends it with vendor-level fulfillment flows. Controls stock levels, reservations, and inventory adjustments. Manages orders, statuses, and returns. Mercur extends it with multi-seller order splitting logic. Integrates payment providers and transaction flows. Used by Mercur for multi-vendor payments and payouts. Defines pricing structures, price lists, and contextual price calculations. Defines products, variants, options, and collections. Mercur adds seller ownership, moderation, and request flows. Handles discounts, promotion rules, and coupon codes. Manages regions, currencies, and tax settings for contextual pricing. Supports product availability across multiple sales channels. Defines physical or virtual locations where inventory is stored. Stores global configuration and metadata for the storefront. Manages tax rules and region-based tax calculations. Handles internal user accounts. Mercur extends this with vendor roles and permissions. --- By keeping all Medusa modules intact and fully accessible, Mercur ensures developers retain complete control over both the **commerce layer** and the **marketplace domain layer**. ---