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I am a Senior Back-End Engineer with over 10 years of hands-on experience designing, building, and deploying scalable, secure distributed backend systems. I specialize in Kotlin and Java, microservices, API development, and cloud infrastructure, with a strong passion for crypto technologies and advancing financial products. I care deeply about code quality, security, and delivering reliable platforms used by millions of users. I lead and mentor cross-functional teams, collaborate closely with product managers, data scientists, and frontend engineers to ship features rapidly while ensuring robustness, maintainability, and extensibility of backend systems.…I am a Senior Back-End Engineer with over 10 years of hands-on experience designing, building, and deploying scalable, secure distributed backend systems. I specialize in Kotlin and Java, microservices, API development, and cloud infrastructure, with a strong passion for crypto technologies and advancing financial products. I care deeply about code quality, security, and delivering reliable platforms used by millions of users. I lead and mentor cross-functional teams, collaborate closely with product managers, data scientists, and frontend engineers to ship features rapidly while ensuring robustness, maintainability, and extensibility of backend systems.

John Lee

Full Stack Developer, Front-End Developer, Web Developer, +3

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I am a Senior Back-End Engineer with over 10 years of hands-on experience designing, building, and deploying scalable, secure distributed backend systems. I specialize in Kotlin and Java, microservices, API development, and cloud infrastructure, with a strong passion for crypto technologies and advancing financial products. I care deeply about code quality, security, and delivering reliable platforms used by millions of users. I lead and mentor cross-functional teams, collaborate closely with product managers, data scientists, and frontend engineers to ship features rapidly while ensuring robustness, maintainability, and extensibility of backend systems.…I am a Senior Back-End Engineer with over 10 years of hands-on experience designing, building, and deploying scalable, secure distributed backend systems. I specialize in Kotlin and Java, microservices, API development, and cloud infrastructure, with a strong passion for crypto technologies and advancing financial products. I care deeply about code quality, security, and delivering reliable platforms used by millions of users. I lead and mentor cross-functional teams, collaborate closely with product managers, data scientists, and frontend engineers to ship features rapidly while ensuring robustness, maintainability, and extensibility of backend systems.

Available to hire

I am a Senior Back-End Engineer with over 10 years of hands-on experience designing, building, and deploying scalable, secure distributed backend systems. I specialize in Kotlin and Java, microservices, API development, and cloud infrastructure, with a strong passion for crypto technologies and advancing financial products. I care deeply about code quality, security, and delivering reliable platforms used by millions of users.

I lead and mentor cross-functional teams, collaborate closely with product managers, data scientists, and frontend engineers to ship features rapidly while ensuring robustness, maintainability, and extensibility of backend systems.

Skills

Experience Level

Expert

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Intermediate

Language

English

Fluent

Work Experience

Senior Full-Stack Developer at Health Hero

September 1, 2025 - September 22, 2025

Built scalable full-stack applications using React/Next.js and Node.js, delivering a seamless user experience while ensuring robust backend performance for real-time data processing. Integrated Retrieval-Augmented Generation (RAG) architecture into a content management system, enabling dynamic, context-aware responses from large datasets. Developed RESTful APIs and real-time dashboards with React and D3.js to visualize AI model performance and RAG outputs for stakeholders. Collaborated with ML engineers to fine-tune models and deployed on a Docker + AWS serverless stack to achieve scalable, cost-efficient operations.

Senior Full-Stack Developer at TechnologyOne

February 1, 2022 - September 22, 2025

Developed AI-driven web applications using Next.js, FastAPI and Django, integrating ML models for real-time data analysis and predictive analytics. Led frontend and backend integration, optimized data pipelines, and contributed to a 30% increase in user engagement through improved UX and responsiveness.

Software Developer at Hobbs

December 1, 2019 - September 22, 2025

Designed and developed a high-performance e-commerce platform using React for the frontend and Node.js for the backend. Integrated payment gateways (Stripe, PayPal) and optimized checkout flows, contributing to a 20% increase in successful transactions. Implemented responsive UI, performance improvements, and scalable frontend/backend architecture.

Web Developer at Cake Solutions

February 1, 2015 - September 22, 2025

Assisted in developing client-facing web applications using HTML, CSS, JavaScript and modern frameworks. Collaborated with senior developers to design and implement responsive frontend features, building dynamic pages with real-time data updates and ensuring maintainable, scalable code.

Senior Full Stack Developer at TechnologyOne

February 1, 2022 - October 21, 2025

Built a scalable AI-powered full-stack application using React/Next.js and Node.js, delivering real-time data processing and robust backend performance. Integrated Retrieval-Augmented Generation (RAG) into a content management system to enable dynamic, context-aware responses from large datasets, improving content accuracy and user engagement by 35%. Developed RESTful APIs to streamline data retrieval and response generation, ensuring smooth communication between backend and ML models in production. Optimized database performance with efficient indexing and query strategies, reducing response times by 50%. Led end-to-end development with ML components using Docker for containerization and AWS Lambda for serverless deployment, enabling scalable, cost-effective solutions. Built real-time dashboards with React and D3.js to visualize AI model performance and RAG outputs for stakeholders.

Software Developer at Hobbs

December 1, 2019 - October 21, 2025

Designed and developed Hobbs, a high-performance e-commerce platform, using React for frontend and Node.js for backend, delivering a seamless user experience and fast loading times. Implemented payment gateways (Stripe, PayPal) and real-time order tracking to boost conversions and customer satisfaction.

Web Developer at Cake Solutions

February 1, 2015 - October 21, 2025

Designed and built responsive web applications, collaborating with senior developers to implement scalable frontend features and maintainable backend components.

Senior Back-End Engineer at HealthHero

February 1, 2022 - December 1, 2025

Led design and implementation of scalable microservices using Kotlin and Java to support AI-powered healthcare applications with high availability and fault tolerance. Built RESTful APIs with PostgreSQL and Redis backends, adopted event-driven architecture using Kafka, and implemented monitoring, security, and CI/CD practices. Championed code quality, testing, and documentation while migrating legacy components to reactive microservices and CQRS patterns to improve scalability.

Back-End Engineer at TechnologyOne

February 1, 2020 - January 1, 2022

Built and maintained distributed backend systems for fintech applications with high fault tolerance. Designed APIs for core financial services integration, utilized PostgreSQL and Redis for storage and caching, and leveraged Kafka for real-time data processing and asynchronous workflows. Drove architectural decisions around reactive programming, event sourcing, security, and cloud-native migrations.

Software Engineer at Hobbs London

March 1, 2015 - December 1, 2019

Developed backend components for e-commerce platforms, integrated third-party payment APIs, and implemented caching layers with Redis. Collaborated with cross-functional teams, performed system design reviews, and supported migration from monolithic to microservices architectures while optimizing database schemas and queries.

Junior Software Developer at Cake Solutions

September 1, 2014 - February 1, 2015

Contributed to backend development projects using Java and Node.js, supported API development and data management with PostgreSQL and Redis, learned test-driven development practices, and participated in agile ceremonies. Gained exposure to microservices architectures and cloud deployment workflows.