API Development for Retail With Commerce Integration, Inventory Sync, POS Connectivity, and Headless Architecture

Our retail API development covers commerce API layer design, inventory integration, order management, payment processing, shipping and fulfillment, and API infrastructure.

Commerce API layer design creates the central API that powers the retail frontend and connects to backend systems. For headless commerce, we build a custom API layer (Node.js or Python) that sits between the frontend application and the various backend services. This layer handles product data aggregation (pulling product information from the commerce engine, availability from the inventory system, pricing from the pricing engine, reviews from the reviews platform, and recommendations from the personalization engine — combining them into a single response for the product page), cart management (maintaining shopping cart state with real-time inventory validation, price recalculation, and promotional rule application), checkout orchestration (coordinating the checkout flow across payment processing, tax calculation, shipping rate calculation, fraud screening, and order creation), and session management (maintaining customer authentication, personalization context, and browsing history across the shopping session). The API layer implements caching at multiple levels — CDN caching for product catalog data, in-memory caching for pricing and availability, and session caching for cart state — to deliver sub-100-millisecond response times for the frontend.

Inventory integration builds real-time synchronization between the systems that track and modify inventory. We connect the ecommerce platform, POS system (for in-store sales and returns), warehouse management system (for receiving, transfers, and adjustments), and marketplace channels (Amazon, Walmart Marketplace) to a central inventory service. The inventory service maintains available-to-sell quantities by location and channel, processes concurrent updates using optimistic locking to prevent overselling, and pushes updates to all connected systems within seconds. For retailers without a dedicated WMS, we build the inventory management logic within the API layer — tracking quantities by location, managing safety stock thresholds, generating reorder alerts, and calculating available-to-promise based on committed inventory (items in carts but not yet purchased) and incoming inventory (purchase orders in transit). The inventory API exposes webhooks for real-time notifications — stock-out alerts to marketing (to pause ads for out-of-stock products), low-stock alerts to purchasing (to trigger reorders), and availability updates to the ecommerce frontend (updating product pages in real time).

Order management integration creates a unified order processing pipeline across channels. We build an order management API that receives orders from all sales channels (website, mobile app, marketplace, POS), normalizes them into a consistent data format, applies business rules for fulfillment routing (ship from the warehouse closest to the customer, ship from the store with the most excess inventory, split orders when no single location has all items), and pushes orders to the fulfillment system. The API tracks order status through the fulfillment lifecycle — picked, packed, shipped, delivered, returned — and pushes status updates back to the originating channel and to the customer via email and SMS notifications. For complex fulfillment scenarios (ship-from-store, buy-online-pickup-in-store, marketplace fulfillment), the order management API implements channel-specific logic while maintaining a unified view of all orders.

Payment processing integration builds a unified payment layer that supports multiple payment methods. We design a payment API that abstracts the differences between payment processors — the frontend calls a single payment endpoint, and the backend routes to the appropriate processor (Stripe, Braintree, PayPal, Affirm, etc.) based on the selected payment method. The payment API handles the complete payment lifecycle: authorization (reserving funds when the order is placed), capture (charging the customer when the order ships), partial capture (for split shipments), refund (full and partial), and dispute handling (webhook processing for chargebacks). The API layer manages PCI compliance — card data never touches the retailer's servers; instead, the frontend uses the processor's client-side tokenization (Stripe Elements, Braintree Drop-in) and the API only handles tokens. Payment retry logic handles transient failures — if a payment authorization times out during a Black Friday checkout, the system retries transparently rather than presenting an error to the customer.

Shipping and fulfillment integration connects the commerce platform to shipping carriers and fulfillment services. We build integrations with shipping carriers (UPS, FedEx, USPS, DHL) for real-time rate calculation, label generation, and tracking updates. For retailers using third-party logistics (3PL) providers (ShipBob, Deliverr, Red Stag), we build the API integration that sends orders to the 3PL for fulfillment and receives tracking and inventory updates in return. The shipping API implements rate caching (pre-computing rates for common package sizes and destinations to reduce API calls during checkout), rate shopping (selecting the cheapest carrier for each shipment based on real-time rates), and delivery date estimation (calculating expected delivery dates based on carrier transit times, warehouse processing times, and cutoff times for same-day shipment).

API infrastructure provides the foundation for reliable, scalable API operations. We implement API gateway configuration (rate limiting, authentication, request routing, CORS management), monitoring and alerting (response time tracking, error rate monitoring, rate limit utilization, and alerts for degradation), documentation (OpenAPI/Swagger specification for all APIs, enabling frontend developers and integration partners to work efficiently), and testing infrastructure (automated integration tests that verify end-to-end flows — placing an order, processing payment, updating inventory, generating shipping labels — against staging environments that mirror production).

Retail API development ranges from $20,000 to $100,000 depending on the number of integrations and complexity. A single system integration (e.g., connecting a B2B platform to Shopify inventory) typically costs $15,000 to $25,000 across 3 to 5 weeks. A commerce API layer for headless architecture (product, cart, checkout, payment, search) runs $40,000 to $80,000 across 8 to 14 weeks. Inventory synchronization across 3 to 5 systems costs $25,000 to $45,000 across 5 to 8 weeks. Order management integration with fulfillment routing costs $20,000 to $40,000 across 4 to 8 weeks. Shipping API with multi-carrier rate shopping and label generation runs $15,000 to $25,000 across 3 to 5 weeks. Ongoing API maintenance, monitoring, and iteration costs $2,000 to $5,000 per month. Infrastructure costs (AWS, database hosting) are additional and typically $200 to $1,000 per month for mid-market retail API workloads.