Senior React Developer (Architecture & Ownership) | AI Product

100% remotely (within Poland only) or in our office: Warszawa Hi, Polcode here! We’re a global, people-first software house matching ambitious developers with challenging projects. Our team of over 100 professionals helps build and improve digital businesses, software platforms, eCommerce stores, websites, apps, and everything in between. And they’re good at it. We’re currently looking for a Senior React Developer (Principal-level mindset) to join a long-term project for an international client building  (with a team based in Berlin) an advanced AI-powered evaluation platform. The product focuses on testing AI agents in simulated scenarios and monitoring their performance in real-world-like conditions. This is not a greenfield project, but a growing and evolving system with strong engineering ownership and architectural challenges. The frontend layer is being actively rethought and rebuilt towards a modern, scalable architecture. In this role, you’ll take a key part in shaping the frontend architecture, including deg a reusable platform and contributing to the transition from a monolithic frontend to a microfrontends-based approach. This role is ideal for a senior engineer who is comfortable taking ownership, making architectural decisions, and naturally stepping into a principal-like role when needed. Why this project is worth your attention: Long-term, stable project until the end of 2026 with high probability of extension Opportunity to shape frontend architecture and influence technical direction Work on a modern frontend platform and microfrontends architecture AI-driven product with real technical depth (not just UI layer) Strong engineering culture and collaboration with experienced backend and AI engineers Small, focused team with direct communication and real ownership Real product, real users, continuous development and evolution. Perks of being a #Polcoder: Multisport card, private medical care, life insurance, and meaningful gifts to celebrate important days All the necessary equipment for comfortable work Professional onboarding process We respect your private life - no overtime, no weekend jobs, work-life balance only, promise! Work at times that suit your daily rhythm, from the place of your choice Your work is appreciated - we believe in the power of feedback, as well as the one you give us. TL;DR Senior React Developer (principal mindset, architecture ownership) Project: AI-powered evaluation platform (microfrontends, scalable frontend architecture) Contract until the end of 2026 with a high probability of extension Remote (with occasional visits to Berlin if needed) B2B: 90-130 PLN/h + VAT Start: April 2026 We strongly believe that putting people first makes our work better. We encourage you to grow your career, contribute to open source, and follow your passion. We wanna do great things with you! 💜 Sounds like a match? Let’s talk!