Senior Full Stack Engineer (Reach)

Team Reach · Helsinki · Hybrid, three office days per week Join Reach at Smartly to build an analytical product that helps customers understand brand marketing performance and make better investment decisions. The work spans interactive interfaces, backend services, data processing, and statistical models. Challenges include deterministic deduplication and frequency distribution estimation: problems where assumptions, edge cases, and validation matter. As a hands-on senior individual contributor, you’ll shape technical decisions, bring people together, and drive initiatives from an initial question to a reliable production solution. What you’ll do Own outcomes. Work with Product and Design to clarify customer needs, choose an approach, and carry initiatives through delivery and follow-up. Build across the stack. Develop data exploration interfaces, backend services and APIs, and the data models and computations connecting them. Make complex logic reliable. Investigate assumptions, reason through edge cases, and establish how to test and validate algorithms and statistical business logic. Drive coordinated delivery. Turn ambiguous goals into manageable steps, agree priorities, coordinate dependencies, surface risks early, and keep colleagues informed. Build shared understanding. Listen to different perspectives, explain trade-offs clearly, and help engineering and business stakeholders reach decisions. Strengthen engineering practice. Contribute through architecture discussions, thoughtful reviews, documentation, mentoring, and improvements to how we work. How we build Our application uses TypeScript, React, and Node.js. We welcome experience with other technologies and value deep understanding of the concepts behind the tools. AI-assisted development is part of how we work. We use coding assistants and agents for exploration, implementation, testing, and review, choosing automation to suit the problem. We judge their value by quality and effort saved. Engineers remain responsible for understanding, validating, and maintaining what they ship. What you’ll bring Senior engineering experience. You’ve designed, shipped, and operated substantial production software and can explain the decisions behind it. Full stack capability with depth. You’re comfortable across frontend, backend, data, and models, with particular strengths and willingness to go deeper where needed. Strong fundamentals. You understand how APIs, data modeling, algorithms, application state, and testing affect correctness, performance, and maintainability. Analytical reasoning. You break unfamiliar problems apart, make assumptions explicit, identify counterexamples, and establish whether a solution is sound. Collaborative leadership. You ask useful questions, build agreement, give and receive constructive feedback, and help colleagues make progress. Practical AI judgment. You provide useful context, critically assess generated output, and verify changes through tests and investigation, considering security, maintainability, and complexity. Experience with analytical products, statistics, or algorithmic systems is valuable. Curiosity and willingness to learn the domain are essential. Why join Reach? Combine product engineering with quantitative challenges, influence the product and its architecture, and grow through hands-on technical leadership and collaboration. Smartly offers healthcare and mental health support, paid holidays and family leave, equity opportunities, and career development opportunities. Learn more about Engineering at Smartly . Our recruitment process Recruiter conversation about your experience and the role. Team lead discussion about expectations and ways of working. Technical interviews covering coding, system design, and architecture. Final conversation with engineering leadership. If you enjoy making complex problems understandable and seeing work through to a use