Senior Fullstack Engineer, Cross-platform

Location: Bulgaria; Lithuania; Armenia; Romania; Estonia; Latvia; Hungary Workplace: Remote WHO ARE WE? Welltech is a global wellness technology company with Ukrainian roots. Our mission is to build and scale wellness apps globally through state-of-the-art, tech-driven performance marketing. We are one of the most established players in the wellness app space, and we are accelerating. Over 25.5 million people across the world use our apps — Muscle Booster, Yoga-Go, and WalkFit — to build healthier habits, move more, and feel better every day. Every subscription represents a real person making a real change in their life, and we take that seriously. With 500+ people across hubs in Cyprus, Ukraine, Poland, Spain, and the UK, we combine the scale of a market leader and the drive of a team that's just getting started. The Product Engineer Mindset We don’t hire people to implement specs. We hire people who can spot the right problem to solve, talk directly to product, design, data, and users to sharpen it, and ship the thinnest version that proves the bet, then iterate. If this is you, you probably: - Measure your work in outcomes, not output. A feature isn’t done when it merges; it’s done when the metric moves, or you’ve learned it won’t, and killed it. - Go to the source. You don’t wait for a perfect PRD. You sit with PMs, designers, marketers, and data, and sometimes users directly, to understand what’s actually being asked. - Own things end-to-end. From the first conversation about a problem through architecture, code, rollout, monitoring, and the follow-up experiment. You don’t hand work off at a boundary. - Have a strong bias to ship. Prototypes, A/B tests, feature flags, kill switches. You’d rather get something in front of users this week than a perfect plan in two months. - Treat AI as leverage, not a novelty. You use agentic workflows to compress the loop between idea and learning, for yourself and the team.   What You’ll Own This is an ownership role, not a feature factory seat. You’ll be on the hook for outcomes across the stack, not just the code in your area: - A cross-platform foundation, end to end. Mobile, web, BFF, and infrastructure layers, built and evolved with an AI-first, agentic development approach, and held to outcomes you helped define. - Scalable foundations for health & fitness apps. React Native and modern web technologies, designed so product teams can ship and experiment faster without rederiving the basics each time. - The discovery loop with stakeholders. Working directly with product, design, marketing, and data to translate business bets into running experiments, not just tickets in a backlog. - AI-agentic workflows across the SDLC. You’ll continuously improve how the team uses AI to raise productivity, code quality, and delivery speed, and prove the impact. - Shared platform capabilities. Internal tooling, CI/CD pipelines, and AI-assisted workflows that make every engineer at Welltech faster and the product better. - Native mobile and media experiences. Video playback, streaming, and HLS, owned from native integration through user-perceived quality. - Modular, reusable systems. Backend-driven UI, white-label capabilities, and the architectural choices that let one team’s work compound for the next. - Reliable integrations. Between frontend clients, BFF services, and platform infrastructure, with you on the hook for the health of the seams. - The engineering culture. Architecture discussions, code reviews or pairing when working on trunk based development workflows, documentation, and continuous improvement, leading by what you ship and how you ship it.   WHAT WE’RE LOOKING FOR Key responsibilities: - Build and evolve a cross-platform ecosystem covering mobile, web, BFF, and infrastructure layers using an AI-first, agentic development approach - Design scalable foundations for health & fitness applications powered by React Native and modern web technologies - Work directly with product, design, and marketing stakeholders to rapidly translate business needs into scalable technical solutions and experiments - Develop and continuously improve AI-agentic workflows across the full development lifecycle to increase team productivity, code quality, and delivery speed - Develop shared platform capabilities, internal tooling, CI/CD pipelines, and AI-assisted workflows that improve development speed and product quality - Work on native mobile integrations and advanced media experiences, including video playback, streaming, and HLS-based solutions - Contribute to modular architectures, reusable systems, backend-driven UI solutions, and white-label application capabilities - Build reliable and scalable integrations between frontend clients, BFF services, and platform infrastructure - Participate in architecture discussions, code reviews, documentation, and continuous improvement of engineering workflows   Required skills: - Strong commercial experience with React Native and modern TypeScript-based application development - Solid understanding of full-stack architecture including mobile, web, BFF, and cloud/infrastructure layers - Experience building scalable cross-platform systems and shared application foundations - Deep understanding of software architecture, modular systems, scalability, and performance optimization - Experience working with CI/CD pipelines, automation tooling, and modern developer workflows - Strong engineering mindset focused on maintainability, reliability, testability, and fast iteration - Comfortable working in AI-assisted or agentic development environments and adopting new AI-driven workflows quickly - Experience with backend-driven UI architectures   Nice to have: - Experience building white-label mobile applications or multi-brand ecosystems - Experience designing and implementing BFF (Backend for Frontend) services - Hands-on backend development experience with TypeScript (Node.js) - Experience building internal developer platforms, shared tooling, or scalable platform capabilities - Familiarity with OWASP mobile security best practices - Experience with engineering methodologies focused on rapid iteration and high developer productivity (Trunk Based Development, CI/CD mindset, TDD, BDD, XP, etc.) - Strong experience with native mobile integrations and media/video playback technologies - Hands-on experience with HLS streaming and native video player integrations on iOS and Android (AVPlayer, ExoPlayer, Chromecast, AirPlay)   Candidate journey: ⭕️ Recruiter call --> ⭕️ Meet a Hiring Manager--> ⭕️ Skills assessment-->Live coding   Check out some of our products Muscle Booster — https://musclebooster.fitness/ Yoga-Go — https://yoga-go.io/ WalkFit - http://walkfit.pro