Full Stack Engineer

Summary

ClassWallet, a leading financial technology company in the United States, is seeking to hire a Full Stack Engineer to join their team. The role involves modernizing a large fintech platform by designing scalable solutions, recognizing and avoiding legacy system pitfalls, and contributing to new services and UI development.

Responsibilities

• 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

Skills

• 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)
• 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

Qualifications

Must Haves

• 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)

Nice to Haves

• 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