Senior Fullstack Developer

Reaktor's tech community is looking for an experienced Senior Fullstack Developer to join one of our Business Units in Helsinki. If you are comfortable working across modern web applications, backend services and production systems, enjoy solving ambiguous problems with clients, and are curious to work in a low-hierarchy environment, you might just be what we’re looking for. You will support clients across a range of digital product, platform and service domains. The exact client context may vary from focused product teams to large international companies working on high-traffic, business-critical services. Many of our clients are technically mature and expect a high level of expertise from our consultants. This means you will need to be hands-on, pragmatic and comfortable helping both the client and the team make good technical decisions. Your daily tasks may include: Building and improving modern web applications, backend services, APIs and data models Working across frontend, backend and infrastructure depending on the needs of the client project Helping clients choose suitable technologies, architecture and delivery approaches Contributing to cloud environments, CI/CD pipelines, deployments and production quality Debugging, testing, monitoring and improving production-grade systems Working on products or tooling related to customer-facing services, internal platforms, identity, martech, customer support, analytics, online stores, integrations, developer tooling or SDKs Collaborating directly with client tech teams, business stakeholders, designers, product people and other disciplines Clarifying ambiguous requirements and turning them into working software Taking responsibility for delivery while making sure the team is supported and no one is left behind Using modern development practices, including openness to AI-assisted development tools and workflows To thrive in this position, you’ll need: Must-haves Strong experience in modern frontend development, for example with TypeScript, , React or comparable technologies Strong experience in backend service development, for example with Node.js, Java, Kotlin, Scala, Clojure, Python or comparable technologies Experience building, shipping and improving production-grade digital products Comfortable working across the full delivery lifecycle, from implementation to testing, deployment and production quality Understanding of cloud environments, CI/CD, deployments and how production systems are operated Ability to work directly with clients, stakeholders and other disciplines in a senior, consultative role Strong problem-solving skills and the ability to bring clarity to ambiguous product or technical situations A hands-on mindset — you are technically credible, actively contribute to the work and help the team move forward Fluent verbal and written English skills to collaborate in an international environment We do not have a hard requirement around years of experience, but we have noticed that this level of fullstack, client-facing and production ownership usually takes several years of professional experience to build. Nice-to-haves Experience from customer-facing digital products, online services, ecommerce, subscriptions, internal platforms, analytics, martech or similar product domains Experience with high-traffic or business-critical production systems Deeper experience with platform engineering, infrastructure-as-code or DevOps practices Experience with customer-facing products, internal tools, integrations, SDKs or developer tooling Familiarity with mobile development or React Native Finnish language skills Adaptability Willingness to work in a hybrid setup. This means balancing office, client premises and remote work depending on the client project and team needs.