Full Stack Engineer

Role Description

We're modernizing a large, business-critical fintech platform. Our current system is a mature Node.js/Express + MongoDB backend (with RabbitMQ workers, batch jobs, and a reports service) paired with a tri-generational frontend — layers of Backbone/Marionette, legacy React class components, and a React + Redux + Material-UI app all coexisting in one codebase.

We're looking for someone with the judgment to tell good patterns from bad ones — who can recognize where the legacy system went wrong, avoid repeating those mistakes in new work, and design scalable solutions that still have to live alongside a rigid, established system. You'll contribute to new NestJS services and Next.js UI, write tests, and ship changes that respect the constraints around you — using AI tooling (Claude Code, Copilot) as a force multiplier, not a crutch.

What you'll do

• Work across the full stack — data model, API contract, UI, and production behavior — contributing to domains as they move onto the modern stack.
• Recognize bad legacy patterns and don't repeat them — read the existing Express/MongoDB and Backbone/React layers, understand where they fell short, and apply better practices in new development rather than carrying old habits forward.
• Design for scale within real constraints — build solutions that scale even when they have to integrate with a rigid legacy system that can't be changed wholesale.
• Build on the modern stack — NestJS modules (DI, guards, interceptors) and Next.js apps (App Router, server components, typed clients).
• Understand the strangler-fig approach — how legacy and new run side by side, behind feature flags, with zero data loss and no downtime — and contribute to it without disrupting it.
• Model relational data carefully — help move money-bearing/transactional data from documents into a normalized SQL schema with real constraints and safe migrations.
• Write tests as a default — unit, integration, E2E. The suite is what lets the team move fast safely.
• Spot and flag problems — the flaky test, the N+1, the missing index. Raise them clearly so they get prioritized, and pick them up when it makes sense.
• Use AI tooling efficiently while understanding and standing behind every line that lands.

Qualifications

• 4+ years shipping production full-stack
• Strong TypeScript front and back · NestJS (or deep Express/Fastify w/ DI grasp)
• Next.js/React (hooks, App Router, SSR/CSR)
• PostgreSQL or MySQL (schema, indexing, transactions, migrations)
• An eye for distinguishing good patterns from bad legacy ones
• Ability to design scalable solutions that fit within an existing, rigid system
• Testing discipline (Jest, Playwright/Cypress, Supertest)
• API design (REST, auth, backward-compatible evolution)

Bonus

• Experience migrating off a legacy code
• Fintech/payments/ledger
• Message queues (RabbitMQ/SQS/Kafka)
• MongoDB/Mongoose Aggregation
• AWS/Docker/Kubernetes/CI
• Deliberate AI-agent use in production workflows

Who you are

• Takes ownership and responsibility for their work
• Eager to take initiative and grow
• Has the judgment to spot bad legacy code and the discipline to not repeat it in new work
• Designs for scale even inside rigid constraints
• Refactors and builds with better practices rather than carrying old patterns forward
• Moves carefully without breaking trust (tests + small PRs + flags)
• Communicates trade-offs clearly
• Raises issues and flags risks rather than routing around them

Our stack

• Today: Node · Express · MongoDB · RabbitMQ · React/Redux · Backbone · Material-UI · AWS · Jest
• Going: NestJS · Next.js · TypeScript end-to-end · PostgreSQL/MySQL · full automated coverage

Benefits

• Excellent salary and benefits commensurate with experience

Company Description

ClassWallet is a positive, family-oriented team environment. Our focus is on encouragement, positive reinforcement, and gratitude. We work hard and are highly motivated to win but with a healthy perspective on life.

ClassWallet.com is proud to be an Equal Opportunity Employer. Applicants are considered for all positions without regard to race, color, religion, sex, national origin, age, disability, sexual orientation, marital or veteran status.