What is a Coupon Code?

A Coupon Code (or Promo Code / Voucher) is a customer-facing string (e.g. WELCOME10, BLACKFRIDAY50) entered into an input field on the cart or checkout page to apply a corresponding discount rule.

Coupons allow merchants to track attribution across specific marketing channels (e.g. influencer campaigns, affiliate links, email newsletters).

Coupon Constraints

To protect profit margins, coupons specify validation conditions:

  • Usage Limits: Maximum number of total redemptions (e.g. First 500 customers).
  • Per-Customer Limit: Maximum redemptions per customer email (e.g. 1 use per customer).
  • Minimum Purchase Requirement: Minimum cart subtotal required (e.g. $50 minimum spend).
  • Expiration Date: Time-bound validity window.

Developer Takeaway

Case-Insensitive Normalization: Always convert coupon codes to uppercase strings (e.g. welcome10 → WELCOME10) before performing database rule lookups to prevent false validation errors for mobile users with auto-capitalization.