Senior Fullstack Engineer, Cross-platform

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