Senior Fullstack Developer

Reaktor

Senior Fullstack Developer at Reaktor building and improving modern web applications and backend services. Collaborating with clients and delivering high-quality digital products in a hybrid setup.

Posted 7/9/2026full-timeHelsinki • 🇫🇮 FinlandSeniorWebsite

Tech Stack

Tools & technologies

ClojureCloudJavaJavaScriptKotlinNode.jsPythonReactReact NativeScalaTypeScript

About the role

Key responsibilities & impact

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

Requirements

What you’ll need

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
Experience from customer-facing digital products, online services, ecommerce, subscriptions, internal platforms, analytics, martech or similar product domains (nice-to-have)
Experience with high-traffic or business-critical production systems (nice-to-have)
Deeper experience with platform engineering, infrastructure-as-code or DevOps practices (nice-to-have)
Experience with customer-facing products, internal tools, integrations, SDKs or developer tooling (nice-to-have)
Familiarity with mobile development or React Native (nice-to-have)
Finnish language skills (nice-to-have)

Benefits

Comp & perks

Willingness to work in a hybrid setup
Flexible working hours

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills & Tools

TypeScriptReactNode.jsJavaKotlinScalaClojurePythonProduction QualityDevOps Practices

Soft Skills

Problem-SolvingCollaborationConsultative RoleHands-On MindsetCommunication