Case study · Credit Karma

Next-gen local development workflow

Modernized Next.js local dev — one dev server and proxy, presets for app state, and MSW mocking so the app runs without a live backend.

Year
2025
next.jsdxtooling

A simpler local dev setup for Next.js — one dev server plus a local proxy, app-state presets, and MSW mocking, so you can iterate without a running backend.

Our Next.js apps needed several processes running to boot locally, and switching app state meant re-seeding data. I rebuilt the loop around one dev server and a lightweight proxy, plus presets you can flip without touching the backend. It's the setup the frontend org — around 1,000 engineers — uses day to day.

Highlights

  • One Next.js dev server and a lightweight local proxy — one port, no CORS wrangling
  • An admin UI to flip presets like authenticated/unauthenticated or device mode
  • A dedicated Mock Service Worker (MSW) server for per-request network mocking
Rendering diagram…
One dev server and proxy, with presets and mocks standing in for the backend

What it changed

Every developer boots the same way — one command, local routing that matches production, and no backend services to stand up first. That also makes local end-to-end testing realistic enough to exercise auth, device, and error states before anything reaches a real service. Onboarding stops being a day of environment setup.

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