Available to hire
Hi, I’m Marcel Olszewski, a senior web developer with 10 years of experience building secure, legally compliant, user-friendly web platforms for regulated industries. I specialize in age-restricted access systems, SMS-based verification, and privacy-first authentication workloads. I design clean, premium interfaces while enforcing strict compliance, and I’m adept at translating complex regulatory constraints into reliable technical solutions.
I thrive in independent, deadline-driven remote work, delivering scalable authentication, multilingual support, and privacy-conscious data handling across global teams. I enjoy collaborating with legal and product stakeholders to turn policy into practical features, and I’m passionate about delivering fast, accessible software that users can trust.
Skills
Experience Level
Expert
Expert
Expert
Expert
Expert
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Expert
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Expert
Expert
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Expert
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Expert
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Expert
Expert
Expert
Intermediate
Intermediate
Intermediate
Intermediate
Language
Polish
Fluent
English
Fluent
Icelandic
Intermediate
Work Experience
Senior Full Stack / Senior Mobile Developer at Glorium Technologies
September 1, 2020 - PresentDelivered a major cross-platform mobile solution using React Native and TypeScript, enabling a 38% boost in feature release velocity across distributed engineering teams. Architected advanced navigation flow with React Navigation and Deep Linking for multi-tenant routing used by over 120K monthly active users. Implemented state management with Zustand and Redux to improve data consistency and reduce unnecessary re-renders by 28%. Built secure API interactions with Node.js services, implementing token rotation and session hardening to reduce authentication failures by 40%. Integrated native modules via Fabric and custom iOS/Android bridges to unlock hardware-level capabilities. Designed automated tests with Jest and Detox, increasing test coverage from 42% to 88%. Optimized FlatList performance, lowering dropped frames by 35%. Led CI/CD improvements with GitHub Actions, achieving a 65% reduction in manual release time.
Full Stack Developer at Selleo EdTech
February 1, 2017 - August 1, 2020Contributed to educational mobile features by integrating React Native components with backend Node.js APIs supporting 30K+ platform users. Built modular React interfaces with reusable components, reducing frontend development time by ~25%. Designed REST endpoints with Node.js, delivering secure APIs for mobile and web clients. Improved load times with granular code splitting and TypeScript refactoring to streamline builds. Implemented session-based authentication across mobile and web apps, preventing unauthorized access. Adopted Redux and later Zustand for state management. Collaborated with QA to automate test scripts, raising coverage for critical components to above 80%. Modernized legacy components into functional React components with hooks, improving readability and performance. Coordinated with product teams to map user behavior, informing UI decisions that boosted engagement. Streamlined CI/CD workflows, reducing manual review steps and increasing release reliability.
Full Stack Developer at Boldare
March 1, 2016 - February 1, 2017Developed foundational UI layers using React, set standards for component reuse and predictable rendering. Created RESTful API features with Node.js to support early mobile client versions. Implemented TypeScript in shared modules, reducing runtime bugs during mobile integration. Worked with designers to refine interaction experiences, contributing to flows later adopted in mobile designs. Established code review guidelines for consistency and maintainability. Introduced automated testing to project pipelines, increasing confidence in rapid iterations. Enabled secure authentication via tokenized API design and built real-time features with WebSockets for mobile synchronization. Performed debugging and optimization to reduce client-side rendering delays. Documented architectural decisions to speed up onboarding.
Senior Backend Engineer at Glorium Technologies
September 1, 2020 - PresentArchitected distributed backend services in Go for financial and data-intensive products used by 500,000+ end users globally. Designed event-driven systems using Kafka to enable asynchronous processing and reduce transaction latency under peak load by 38%. Implemented highly available Cassandra data models, sustaining 99.99% uptime across critical services. Orchestrated containerized microservices with Kubernetes and Docker, supporting horizontal scaling during traffic spikes 4x baseline. Integrated Envoy proxy and gRPC-based communication to standardize inter-service networking and reduce API error rates by 27%. Deployed production workloads on AWS with cost optimization through right-sizing and autoscaling. Collaborated daily with product managers, designers, analysts, and QA to align backend architecture with measurable customer outcomes. Led system design initiatives to address ambiguity in early-stage requirements while ensuring long-term maintainability and fault tolerance. Built
Full Stack Developer at Selleo
February 1, 2017 - August 1, 2020Developed backend services for education and SaaS platforms, supporting tens of thousands of daily active users. Engineered RESTful APIs in strongly typed languages, improving data consistency and reducing integration defects by 20%. Implemented asynchronous workloads to handle background processing and long-running tasks efficiently. Designed relational and NoSQL schemas to balance performance, scalability, and maintainability. Containerized applications using Docker, simplifying local development and accelerating release cycles by 35%. Deployed cloud infrastructure on AWS, ensuring secure and reliable production environments. Collaborated with product stakeholders to translate business requirements into scalable technical solutions. Improved system observability through enhanced logging and monitoring, reducing production issue diagnosis time. Contributed to frontend features with React for seamless integration with backend APIs. Participated in architectural discussions around modul
Senior Full Stack Engineer (Back end-Focused) at Glorium Technologies
September 1, 2020 - PresentArchitected backend systems supporting complex search and booking workflows, serving over 250,000 monthly active users across multiple platforms. Engineered integrations with six external APIs ensuring data normalization, error handling, and uptime above 99.95%. Designed scalable Node.js and Python microservices to process real-time availability, pricing, and booking confirmations. Optimized PostgreSQL and MongoDB queries, reducing average search response times by 38%. Implemented secure authentication and authorization, plus API caching and rate-limiting that cut third-party API costs by 27%. Collaborated with frontend teams to enhance React-based interfaces and delivered robust logging, monitoring, and GDPR-compliant data handling. Led backend documentation and introduced asynchronous processing to handle peak traffic.
Full Stack Developer at SELLE O EdTech
February 1, 2017 - August 1, 2020Built backend services for content discovery and booking-style platforms, enabling structured search and filtering experiences. Integrated multiple external APIs to aggregate third-party data into unified workflows. Developed RESTful services using Node.js to support scalable, data-driven web applications. Implemented relational and NoSQL database schemas supporting complex query requirements. Improved backend performance through indexing and query optimization, achieving around 30% faster load times. Collaborated with designers and frontend developers to ensure a seamless UX across React-based interfaces. Implemented authentication flows and role-based access control for multi-tenant platforms. Delivered production-ready features on tight timelines while maintaining code quality and documentation.
Senior Web Developer at Glorium Technologies
September 1, 2020 - PresentArchitected legally compliant web platforms for regulated industries, supporting 18+ age-restricted access and jurisdiction-specific requirements. Delivered SMS-based phone verification workflows using Twilio, reducing fraudulent access attempts across client platforms. Designed clean, premium user interfaces that balanced strict legal gating with friction-minimal onboarding. Implemented secure age-verification flows enforcing access control before product visibility, meeting regulatory audit standards. Integrated multilingual support systems enabling seamless language switching without duplicating application logic. Established privacy-first data handling practices aligned with GDPR and regional compliance mandates. Developed secure authentication APIs using Node.js and JWT, improving login reliability. Collaborated with legal stakeholders to translate regulatory language into enforceable technical rulesets. Built reusable compliance components to accelerate delivery timelines across
Education
Bachelor of Computer Science at The University of Queensland
January 1, 2011 - January 1, 2015Bachelor of Computer Science at The University of Queensland
January 1, 2011 - January 1, 2015Bachelor of Computer Science at The University of Queensland
January 1, 2011 - January 1, 2015Bachelor of Computer Science at The University of Queensland
January 1, 2011 - January 1, 2015Qualifications
Industry Experience
Software & Internet, Professional Services, Media & Entertainment, Education, Financial Services
Skills
Experience Level
Expert
Expert
Expert
Expert
Expert
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Expert
Expert
Expert
Expert
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Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Expert
Intermediate
Intermediate
Intermediate
Intermediate
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