Kueski Pay Extension

Kueski Smart Widget

Kueski Pay in the browser: coupons, balance and checkout, right when you're about to buy.

STACK
JavaScript · Chrome Extensions (Manifest V3) · Node.js · Express · PostgreSQL
STATUS
Prototype · delivered May 2026
View code ↗
Kueski Pay Extension screenshot

OVERVIEW

Kueski, Mexico's buy-now-pay-later platform, wanted people to use it more often — but reaching it meant opening the app, signing in and finding the right screen. Kueski Smart Widget is a Chromium extension that brings it to the moment of purchase: it recognises affiliated stores, shows the offer on the page, and lets you check your balance and pay in fortnightly instalments without leaving the site. Built by a team of four with Kueski as industry partner.

WHAT I FOUND → WHAT I DECIDED

  • No extension in Mexico pairs store coupons with access to a buy-now-pay-later balanceBuild around both: tier-scaled coupons on affiliated stores, next to your available credit
  • Manifest V3 forbids remote code and a strict CSP blocks inline scriptsPlain JavaScript with no framework or build step, and one delegated click handler instead of inline events
  • In a survey of 45 online shoppers, data security was the top barrier to installing a financial extensionThe server revalidates every sensitive action, and anything from the backend is escaped before it reaches the page
  • Two concurrent requests could pay the same instalment twicePay inside a transaction that locks the instalment row first

WHAT IT DOES

DETECT
Recognises affiliated stores, marks the toolbar icon and anchors an offer banner to the site's header.
COUPONS
Copyable coupon codes whose discount scales with the user's credit tier.
CHECKOUT
Reads the product or cart total from the page and splits it into 3, 6 or 12 fortnightly payments.
BALANCE
Available balance, credit usage and upcoming payments, one click from any page.
CARD
A virtual card whose CVV is generated on demand and never stored.
STORES
Browse affiliated stores with search and category filters.

HOW IT WAS BUILT

Started from research: sessions with Kueski, their brief, a review of Honey, Rakuten and Capital One Shopping, and a survey of 45 online shoppers. The extension runs in three browser contexts — popup, content script and service worker — over a stateless Node and PostgreSQL API. It was checked with 30 functional test cases across three demo credit profiles, including the actions a restricted profile must be refused.

SCREENS