Christian L.

I build production-grade frontends for B2B SaaS products with React, Next.js and strict TypeScript. Over the last 3 years I've been the main person responsible for the frontend on platforms in fintech (bookkeeping and payroll) and logistics, integrating real financial services like Plaid, Stripe and AWS Cognito. What I'm good at: - React 19, Next.js (App Router, RSC), TypeScript strict mode - Building entire features end to end: from data fetching with TanStack Query to forms with React Hook Form + Zod validation - Frontend architecture for products that need to scale: I use Domain-Driven Feature and Feature-Sliced Design depending on the project's complexity - Data-heavy UIs: tables with thousands of rows, dashboards with real-time state, complex multi-step forms - Integrations with REST APIs, WebSockets, third-party services (Plaid, Stripe, AWS Cognito, Google Maps, Twilio, Payarc) - Testing strategy with Vitest and Playwright when the project needs it What kind of projects fit me best: - B2B SaaS products that need a serious frontend engineer, not just someone who can put components on a page - Existing codebases that need refactoring, performance work, or architectural improvements - New projects in fintech, logistics, dashboards, internal tools How I work: I communicate clearly and early, especially when something is unclear or when I see a better way to solve a problem. I don't disappear on the client. I treat code reviews seriously — every line I write, I can explain why it's there. I'm based in Medellín, Colombia (UTC-5), which overlaps well with US business hours. I'm new to Upwork but not new to building real products. If you want to see how I write code or how I approach a problem, I'm happy to share examples on a quick call before you commit.