Cart & Checkout

The highest-leverage surface in commerce: where intent becomes revenue. Design carts and checkouts that are correct under concurrency and optimized for completion — without prescribing a framework.

Before Starting

Gather: cart model (server-persisted vs client, guest vs account), checkout type (single vs multi-step), payment/shipping/tax requirements, and goal (design new flow, audit drop-off, or build abandoned-cart recovery).

How This Skill Works

Mode	Trigger	Output
Design	design	Cart state model + checkout step flow + edge cases
Audit	audit	Friction/drop-off analysis with prioritized fixes
Abandoned	abandoned	Recovery sequence (triggers, timing, channels)

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Phase 1 — Cart State

Decision	Recommendation
Persistence	Server-side cart keyed by session + user; merge on login
Pricing	Re-price at checkout — never trust cart-stored prices
Inventory	Soft-reserve at checkout start, not on add-to-cart
Identity	Allow guest carts; merge guest → account without losing items

Rule: The cart is a draft, not a contract. Totals, stock, and promotions are recomputed server-side before payment.

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Phase 2 — Checkout Flow

Canonical steps: Cart → Identity → Shipping address → Shipping method → Payment → Review → Confirmation.

• Guest checkout is non-negotiable for B2C — forced account creation is the #1 avoidable drop-off.
• Collect email first (enables abandoned-cart + receipts).
• One-page vs multi-step: multi-step for complex shipping/tax; one-page for low-SKU/digital. Either way, show progress and never lose entered data on validation error.
• Recompute tax/shipping when the address changes; show the final total before the pay button.
• Make payment idempotent — a double-click must not double-charge (hand off to payments-architecture).

For the full step-by-step field list, error handling, and address validation patterns, see references/checkout-flow-spec.md.

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Phase 3 — Abandoned-Cart Recovery

Touch	Timing	Angle
1	~1h	Reminder ("you left these")
2	~24h	Help/objection handling + reviews
3	~72h	Incentive (discount) — only if margin allows

Capture email as early as possible; suppress recovery once the order completes; respect consent and frequency caps.

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Output Artifacts

Request	Output
Design flow	Cart model + annotated step diagram + edge-case list
Audit	Drop-off table with severity and READY-to-ship fixes
Abandoned	Trigger/timing/channel sequence + suppression rules

A checkout is READY when guest checkout works, prices/stock are re-validated server-side, payment is idempotent, and data survives validation errors.

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Related Skills

• payments-architecture: owns the payment step (intents, idempotency, webhooks).
• shipping-tax: computes the shipping and tax shown at checkout.
• promotions-discounts: applies coupons/discounts at the cart.
• page-cro / form-cro: deeper conversion optimization of the checkout UI.
• order-lifecycle: takes over once the order is placed.