Senior Full-Stack Kotlin Engineer (Freelance/Service Agreement)

🏢 Summary: Full-Stack Software Engineer role building a high-scale e-commerce PPC platform with React microfrontends and Kotlin/Spring Boot services. The work spans real-time analytics dashboards, ML-driven recommendations, and event-driven campaign-data processing, with strong automated testing and DevOps practices. 🗂️ Requirements: Proven React expertise, TypeScript proficiency, CSS and HTML proficiency, State-management experience, Modern testing-framework experience, Hands-on Kotlin and Spring Boot experience, REST API and microservices experience, Commercial MongoDB and SQL experience, Cloud-environment experience, Familiarity with agentic coding assistants, English proficiency at B2 or higher 📃 Skills: React, TypeScript, CSS, HTML, Jest, Vitest, Playwright, Kotlin, SpringBoot, REST, MongoDB, SQL, GCP, GitHubCopilot, OpenCode 🏢 Description: We're looking for Full-Stack Software Engineer (React & Kotlin). Join a high-scale, PPC advertising platform in the e-commerce sector, built entirely on microservices handling thousands of requests per second. You will work on ML-driven recommendation engines, high-volume event data pipelines, and real-time merchant analytics dashboards. Our expectations Frontend Focus: Strong, proven expertise in React, TypeScript, CSS/HTML , state management, and modern testing frameworks (Jest / Vitest / Playwright). Backend Proficiency: Solid hands-on experience in Kotlin with Spring Boot, REST APIs, and microservices architecture. Commercial experience working with MongoDB, SQL databases, and cloud environments (GCP preferred). Familiarity with agentic coding tools and assistants (e.g., GitHub Copilot, OpenCode). Proactive, relational, highly engaged, open-minded, and strong communication skills. Fluent in English (B2+). Welcome Skills Experience with Microfrontends, Server-Side Rendering (SSR), and Accessibility standards (a11y / WCAG). Exposure to Scala, Big Data engines (Apache Spark), or search technologies (ElasticSearch). Prior background in AdTech, PPC advertising, or large-scale e-commerce systems. Key tasks Design, build, and maintain scalable React-based microfrontends for analytics dashboards and merchant tools with a focus on Accessibility (a11y) and Server-Side Rendering (SSR). Build high-performance backend microservices in Kotlin and Spring Boot to power real-time dashboards, benchmarks, and recommendation engines. Partner closely with Data Science teams to serve personalized recommendations and automated campaign insights. Participate in developing a distributed, event-driven cloud architecture for processing campaign data in real time. Maintain high engineering standards through automated testing (unit, integration, E2E via Jest/Vitest/Playwright), code reviews, CI/CD, and DevOps practices.

🏢 Summary: Długoterminowy, w pełni zdalny projekt B2B dla Senior Full Stack Developera rozwijającego wewnętrzny system leasingowy w środowisku międzynarodowym. Rola obejmuje rozwój backendu w Kotlinie i Spring Boot, frontendu w React oraz migrację usług z Node.js do Kotlina. 🗂️ Requirements: Minimum 7 lat komercyjnego doświadczenia jako Software Engineer, Bardzo dobra znajomość Kotlina, Bardzo dobra znajomość Spring Boot, Doświadczenie w React, Praktyczna znajomość PostgreSQL, Praktyczna znajomość MongoDB lub innych baz NoSQL, Doświadczenie z architekturą mikroserwisową, Znajomość procesów CI/CD, Doświadczenie z narzędziami AI wspierającymi development, Język angielski na poziomie C1 📃 Skills: Kotlin, SpringBoot, React, PostgreSQL, MongoDB, NoSQL, Microservices, CI/CD, Claude, Copilot, ChatGPT 🏢 Description: 📍 100% zdalnie | B2B | Długoterminowy projekt Dla naszego klienta poszukujemy Senior Full Stack Developera , który dołączy do zespołu rozwijającego i utrzymującego wewnętrzny system leasingowy wykorzystywany w międzynarodowym środowisku. To projekt nastawiony na długofalowy rozwój produktu. Na co dzień będziesz pracować głównie z Kotlinem po stronie backendu oraz Reactem po stronie frontendu . Część istniejących usług nadal działa w Node.js i jest sukcesywnie migrowana do Kotlina. Twoja rola Będziesz odpowiedzialny za rozwój nowych funkcjonalności oraz utrzymanie istniejącego systemu, współpracując z doświadczonym zespołem programistów. Do Twoich zadań będzie należało: rozwój aplikacji backendowych w Kotlinie i Spring Boot, rozwój interfejsów użytkownika w React, udział w migracji części usług z Node.js do Kotlina, projektowanie i rozwój architektury mikroserwisowej, dbanie o jakość kodu, testy oraz code review, współpraca z zespołem produktowym i udział w decyzjach technicznych, wykorzystywanie narzędzi AI wspierających development. Szukamy osoby, która posiada minimum 7 lat doświadczenia komercyjnego jako Software Engineer, bardzo dobrą znajomość Kotlina oraz Spring Boot, doświadczenie z React, praktyczną znajomość PostgreSQL oraz MongoDB lub innych baz NoSQL, doświadczenie z architekturą mikroserwisową, znajomość procesów CI/CD, doświadczenie w pracy z narzędziami AI wspierającymi development (np. Claude Code, GitHub Copilot, ChatGPT), język angielski na poziomie C1 umożliwiający swobodną pracę w międzynarodowym środowisku. Mile widziane Docker, Kubernetes, AWS, Amazon SQS, doświadczenie w środowisku SaaS, znajomość Node.js. Oferujemy długoterminową współpracę w modelu B2B, pracę 100% zdalną, nowoczesny stack technologiczny, możliwość pracy przy rozwoju produktu wykorzystywanego w międzynarodowym środowisku, realny wpływ na rozwój systemu i decyzje techniczne, współpracę z doświadczonym zespołem specjalistów. Technologie Backend Kotlin • Spring Boot • Java • Node.js Frontend React • TypeScript Bazy danych PostgreSQL • MongoDB Cloud & DevOps AWS • Docker • Kubernetes • CI/CD • Amazon SQS AI Claude Code • GitHub Copilot • ChatGPT

🏢 Summary: Senior Full Stack Engineer role focused on leading the delivery of scalable, business-critical web applications. The position combines React/Remix front-end development with Python REST APIs, Azure cloud deployment, automated testing, and DevSecOps practices while providing technical leadership in an Agile team. 🗂️ Requirements: Senior full-stack engineering experience, TypeScript, React, Python, RESTful API development, MongoDB, SQL databases, Microsoft Azure, Azure Kubernetes Service, Clean, testable code, Test-driven development, Vitest, Pytest, DevSecOps practices, GitHub workflows, GitHub Actions CI/CD, Kubernetes, ArgoCD, Problem-solving, Technical communication, Bachelor’s degree or equivalent professional experience 📃 Skills: TypeScript, React, Remix, Python, MongoDB, SQL, Azure, AKS, Vitest, Pytest, GitHub, GitHubActions, Kubernetes, ArgoCD, DevSecOps, TDD, GitOps, ES6 🏢 Description: We are seeking an experienced Senior Full Stack Engineer to join a high-performing engineering team responsible for building and enhancing innovative web-based platforms. This role offers the opportunity to work on complex, business-critical applications while driving technical excellence, engineering best practices, and scalable software solutions. As a Senior Engineer, you will take ownership of advanced development initiatives, contribute to architectural decisions, and help shape the future direction of modern web applications. You will work across both front-end and back-end technologies , combining expertise in React-based user interfaces and Python API development to deliver secure, scalable, and maintainable solutions. The ideal candidate will have strong full-stack engineering experience, a passion for clean code and automation, and the ability to solve complex technical challenges within a collaborative, agile environment. Key Responsibilities Lead the design, development, and delivery of complex software engineering initiatives from concept through to production. Architect and build scalable Python RESTful APIs and modern React/Remix-based web applications using service-oriented architecture principles. Develop reusable components, integrations, and technical solutions that improve application scalability and maintainability. Investigate, troubleshoot, and resolve complex technical issues, providing effective solutions and long-term improvements. Establish and promote engineering best practices across development, testing, security, and deployment processes. Champion a DevOps-first mindset , supporting automation, continuous delivery, and operational excellence. Define and address non-functional requirements including performance, accessibility, reliability, and security. Collaborate closely with Product Owners, architects, engineers, and business stakeholders to translate requirements into innovative technical solutions. Provide technical guidance and mentorship to other engineers, encouraging knowledge sharing and continuous improvement. Contribute to Agile delivery practices, supporting effective planning, estimation, and iterative development. Essential Skills & Experience Proven experience as a Senior Full Stack Engineer or similar technical leadership role, delivering complex software solutions. Strong proficiency in TypeScript , including modern ES6+ features and best practices. Extensive experience building dynamic, responsive front-end applications using React , with experience in Remix or similar frameworks preferred. Strong backend development experience using Python , including the design and implementation of RESTful APIs. Solid understanding of database technologies, including MongoDB and relational SQL databases. Hands-on experience with Microsoft Azure , particularly Azure Kubernetes Service (AKS) and cloud-native application deployment. Strong commitment to writing clean, maintainable, and highly testable code. Experience with Test Driven Development (TDD) and automated testing frameworks, including: Unit testing with Vitest and Pytest Functional testing exposure with Playwright is desirable. Strong understanding of modern DevSecOps practices , including: GitHub version control workflows CI/CD automation using GitHub Actions Containerised application deployment using Kubernetes GitOps practices with ArgoCD Excellent problem-solving skills with strong attention to technical detail and quality. Strong communication skills with the ability to collaborate effectively with both technical and non-technical stakeholders. Bachelor’s degree in Computer Science, Engineering, or a related discipline, or equivalent professional experience. Desirable Skills Azure Developer certification, particularly AZ-204 . Experience working with Databricks or modern data platforms. Experience working in Scrum-based Agile environments . Previous experience working with large-scale enterprise applications and distributed systems.

🏢 Summary: Build and scale native Android features for an international consumer fintech platform. The role focuses on reliable payment and account-management journeys, REST API integrations, mobile performance, and data-driven product improvements. 🗂️ Requirements: 3+ years of commercial Android development experience, Kotlin proficiency, Experience shipping production Android apps at scale, Strong Android fundamentals, Jetpack components expertise, Coroutines and Kotlin Flow expertise, Modern Android architecture experience (MVVM/MVI), REST API integration experience, Production issue debugging experience, UI/UX, edge-case, and state-management expertise 📃 Skills: Android, Kotlin, Jetpack, Coroutines, Flow, MVVM, MVI, REST, Telemetry, Analytics 🏢 Description: Overview We are looking for a product-minded Android Software Engineer to build and scale features for an international consumer fintech platform. You will work on clean user journeys, high performance, and reliable mobile architectures for a large user base. Key Responsibilities Develop and deploy native Android features using Kotlin. Design clean mobile flows for payments, financial transactions, and account management. Collaborate with product and design teams to simplify complex financial workflows. Integrate backend REST APIs to build stable, secure, and responsive user flows. Optimize app performance, including crash rates, loading states, memory footprint, and UI responsiveness. Implement smart, data-driven mobile features that improve the overall user experience. Use telemetry, analytics, and crash reporting tools to continuously iterate on product quality. Qualifications 3+ years of commercial Android development experience using Kotlin. Proven track record of shipping production apps at scale with solid Android fundamentals. Strong proficiency in Jetpack components, Coroutines, Kotlin Flow, and modern Android architecture (MVVM/MVI). Practical experience with REST API integration and debugging complex production issues. Sharp eye for UI/UX details, edge cases, and smooth state management. High ownership, fast execution speed, and strong code quality standards.

🏢 Summary: Hybrid Senior Fullstack Engineer role in Warsaw focused on building intelligent advertising and campaign-management tools. The position combines Kotlin backend development, React microfrontends, GCP-based event-driven systems, APIs, and data-intensive recommendation capabilities. 🗂️ Requirements: 3+ years of full-stack development experience, React and Kotlin experience, Proficiency in TypeScript, HTML/CSS, Spring Boot and microservices, Cloud ecosystem experience, preferably GCP, MongoDB and SQL database experience, Event-driven architecture and large-scale data processing knowledge, Polish and English communication skills, Agile software delivery experience, Existing legal right to work in the European Union 📃 Skills: React, Kotlin, TypeScript, HTML, CSS, Spring, Boot, GCP, MongoDB, SQL, Jest, Vitest, Playwright, Microservices 🏢 Description: Unleash innovation — design the future of intelligent advertising ecosystems! Warszawa-based opportunity with hybrid work model. As a Senior Fullstack Engineer – React and Kotlin Specialists , you will be working for our client, a leader in building advanced advertising tools, focusing on creating intelligent recommendation systems and automating campaign management for advertisers on Allegro Ads. Join a mission-driven project that revolutionizes how businesses grow through cutting-edge technology and data-driven insights, offering exciting avenues for professional growth and innovation. Your main responsibilities: Develop and maintain backend services using Kotlin, integrating machine learning-driven recommendation engines in collaboration with data science teams. Build scalable, event-driven architectures to process large data volumes within cloud environments, leveraging GCP. Design and implement high-performance APIs to support analytical dashboards and market benchmarks. Create and optimize scalable microfrontends using React, prioritizing accessibility and server-side rendering for analytical tools. Collaborate with cross-functional teams to deliver seamless, secure, and efficient software solutions. Ensure high code quality through testing frameworks such as Jest, Vitest, or Playwright, with a focus on performance and reliability. Contribute to evolving microservice architectures, utilizing Spring Boot, MongoDB, SQL, and cloud-native tools. Participate actively in code reviews, sprint planning, and technical discussions to foster continuous improvement. You're ideal for this role if you have: At least 3 years of experience in full-stack development, with a focus on React and Kotlin. Strong proficiency in TypeScript, React, HTML/CSS, and backend technologies like Kotlin, Spring Boot, and microservices. Experience working with cloud ecosystems, preferably GCP. Solid understanding of database management, including MongoDB and SQL. Familiarity with event-driven architectures and large-scale data processing. Ability to communicate effectively in Polish and English. Experience working in an Agile environment with a focus on delivering high-quality software. It is a strong plus if you have: (optional) Certifications related to GCP or microservices architecture. Experience with agentic coding tools like Copilot/OpenCode. Knowledge of accessibility standards (a11y) and performance optimization techniques. Language Required for the role: Polish (Communicative) English (Communicative) Eligibility for this role: Only candidates with an existing legal right to work in the European Union will be considered for this role. #MAKEYourCareerBETTER Interested? Apply now and include your CV (preferably in English) along with a statement confirming your consent to the processing and storage of your personal data.

🏢 Summary: Full Stack Developer role focused on fixing and enhancing an existing demand-planning application. The position involves building scalable TypeScript/JavaScript web applications, Vue.js interfaces, and Node.js/Nest.js APIs while collaborating with data engineers and product stakeholders. 🗂️ Requirements: Full Stack development experience, TypeScript, JavaScript, Vue.js, Node.js, Nest.js, PostgreSQL, MySQL, or MongoDB, RESTful API development and integration, Git-based version control, Agile development experience 📃 Skills: TypeScript, JavaScript, Vue.js, Node.js, Nest.js, PostgreSQL, MySQL, MongoDB, REST, Git, GitHub, GitLab, Bitbucket, Azure, Docker, Kubernetes 🏢 Description: Description Help resolve issues in an existing demand-planning application and develop new features. Requirements • Proven experience as a Full Stack Developer specializing in TypeScript and JavaScript • Strong proficiency with Vue.js • Solid understanding of Node.js and Nest.js • Experience with PostgreSQL, MySQL, or MongoDB • Knowledge of RESTful API development and integration • Familiarity with Azure is a plus • Experience with Docker and Kubernetes is a plus • Proficiency with Git, GitHub, GitLab, or Bitbucket • Strong problem-solving skills and ability to work in an agile environment • Excellent communication skills and a collaborative mindset Responsibilities • Develop and maintain scalable web applications using TypeScript and JavaScript • Design and implement responsive front-end interfaces with modern frameworks • Build and optimize server-side logic and APIs to improve application performance • Collaborate with cross-functional teams, including Data Engineers and product managers • Ensure code quality, performance, and security through best practices and testing • Work independently and collaborate with stakeholders • Participate in code reviews and provide constructive feedback • Maintain technical documentation and contribute to the team knowledge base • Stay current with web-development trends and best practices We offer • Flexible working format: remote, office-based, or flexible • Competitive salary and compensation package • Personalized career growth • Professional development tools, including a mentorship program, tech talks, training, and centers of excellence • Active tech communities with regular knowledge sharing • Education reimbursement • Anniversary presents • Corporate events and team buildings • Other location-specific benefits