Cartwell: Transparent Substitution & Price Diffing
A customer-centric quick commerce checkout architecture that prevents basket abandonment during in-store inventory stockouts by establishing per-item substitution policies and transparent line-item price adjustments prior to fulfillment.
Live Substitution Matrix Simulator
Step through the weekly grocery replenishment flow. Review the basket, set substitution policies for Organic Milk and Sourdough Bread, trigger a simulated picker stockout event, and inspect the real-time line-item price reconciliation.
Cartwell Substitution Matrix & Price Diff
Your Grocery Basket
Market St. Express · 4 Items1. Operational Scenario: The In-Store Stockout Dilemma
In on-demand grocery delivery and quick-commerce operations, physical retail shelf inventory shifts continuously as walk-in customers deplete stock. A family grocery shopper placing a weekly repeat order for staples—such as organic whole milk, artisanal bread, and fresh fruit—expects their order to arrive complete and on time.
Meanwhile, inside the retail fulfillment center, an in-store picker reaches the dairy cooler only to discover the last gallon of organic whole milk was purchased ten minutes prior. In standard grocery apps, this moment triggers one of two catastrophic customer failures: either the picker makes an unauthorized brand substitution that violates family dietary restrictions, or the entire basket is delayed or cancelled.
2. The Inventory Hurdle: Why Traditional Grocery Apps Fail
Most ecommerce architectures treat grocery shopping like physical dry goods: an item is assumed in stock until an error occurs. When applied to fast-moving perishables, this causes acute friction:
- !The Unwanted Substitution Surprise: Algorithms or rushed pickers replace lactose-free milk with conventional dairy, or gluten-free bread with wheat, leading to health hazards and customer chargebacks.
- !Silent Price Inflation: A premium brand replacement is inserted at a higher price without explicit pre-authorization, leading to surprise credit card debits and negative reviews.
- !Basket Dumping & High Drop-Off: If an essential ingredient cannot be fulfilled, customers often abandon the entire order rather than proceeding with an incomplete recipe manifest.
3. The Architecture: Pre-Checkout Substitution Matrix
Cartwell resolves inventory friction by moving substitution preferences from an ad-hoc post-checkout panic to an explicit pre-checkout configuration matrix:
Core Architectural Pillars
4. Demonstrated UX Decisions in the Interface
Shoppers set their preferences with one tap right on the cart screen, avoiding confusing popups during checkout.
Clear green (+/-) badges display exact variance per item and compute the net refund or balance before driver departure.
5. Interface State Map & Exported Screens
Direct pixel exports generated from the interface state machine:
4-item grocery cart with per-item substitution policy badges and estimated subtotal.
Item-level preferences: Brand Match, Any Organic Match, Lactose-Free Alternative, or Refund Only.
In-store alert flagging depleted shelf and automatically applying pre-configured substitution rules.
Line-by-line price reconciliation showing replacement premium and instant refund debit.
6. Edge Case Resilience Matrix
If an acceptable organic substitute costs more than a 15% ceiling above original item price, Cartwell automatically defaults to “Refund Only” rather than triggering unauthorized overcharges.
The picker mobile client caches all substitution preference rules locally in SQLite. In-store dead zones never block picking flow.
7. Technical Distinction & Target Architecture
Browser client prototype executing local React state transitions. Simulates inventory stockouts and dual-ledger price calculation in real time.
Target production application built with Flutter for 60fps catalog browsing and Go microservices processing real-time inventory ledger updates and Stripe capture webhooks.
Project Parameters
Observed vs. Target Metrics
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