Ecommerce

## Quick Reference | Topic | File | |-------|------| | Code traps that break production | `code-traps.md` | | Platform comparison (costs, features) | `platforms.md` | | Operations (stock, shipping, returns) | `operations.md` | | Growth (CRO, upsells, LTV, benchmarks) | `growth.md` | ## Critical Code Traps These break production and cost real money. See `code-traps.md` for full patterns. 1. **Payment idempotency** — Store `payment_intent_id`, check before processing. Webhooks retry. 2. **Inventory race conditions** — `UPDATE ... WHERE stock > 0` with `rowsAffected` check, not read-then-write. 3. **Frontend price trust** — Backend recalculates everything. Never trust client totals. 4. **Webhook signatures** — Verify `stripe-signature` or equivalent. Reject unsigned requests. 5. **Stock validation timing** — Verify at payment moment, not just add-to-cart. ## Core Rules ### When Building Stores - Calculate ALL prices server-side — discounts, shipping, taxes, totals - Queue transactional emails — never inline in checkout flow - Add structured data (Schema.org Product) and canonical URLs from day one - Implement webhook signature verification before going live ### When Operating Stores - Monitor stock thresholds, not just zero — alert at reorder point - Track orders stuck in "processing" >24h — detect before customer complains - Log payment failures with context — card decline reasons matter for recovery ### When Optimizing - Checkout recovery: 1h, 24h, 72h sequence — discount on email 3, not 1 - Free shipping threshold: current AOV + 20-30% - Mobile: sticky add-to-cart, Apple Pay/Google Pay, LCP <2.5s ## Platform Decision Tree - **Budget <€500/mo, <100 SKUs**: Shopify Basic or WooCommerce self-hosted - **Multi-marketplace**: Dedicated sync tool (not manual updates) - **>1000 SKUs or ERP**: WooCommerce/custom with PIM integration For Spain-specific costs (IVA, OSS, carriers), see `platforms.md`. ## Scope This skill helps with: - Store architecture and payment integration - Inventory and order management logic - Marketplace listing optimization - Conversion rate tactics with benchmarks - Legal/fiscal guidance for EU/Spain ecommerce This skill does NOT: - Connect to live store APIs (explain how, not execute) - Store business data or credentials - Make purchasing or pricing decisions autonomously