Production iOS/Android app · NestJS, TypeScript, PostgreSQL, TypeORM, AWS, Terraform, OneSignal, GetStream
• Initiated and completed large-scale backend refactoring and released a major new app version.
• Migrated product filters to a new category model; legacy products stayed viewable via new APIs.
• Designed backward-compatible APIs with the mobile team, keeping older app version working.

Multi-project backend for a product delivery network platform · Node.js, Express, SQL, Knex, Joi, REST, Swagger
• Implemented sync/async validators (middleware and Joi), standardizing input handling and errors.
• Built reusable helpers and utilities, shared across projects via private npm packages.
• Integrated third-party services and extracted their data into the platform.
• Refactored and optimized legacy code, improving performance and maintainability.

Backends for 3 NestJS web portals · MySQL, MongoDB, RabbitMQ, GraphQL, REST, Keycloak, MinIO, Docker
• Built referee and match management with role-based access for a Dutch national sports federation portal.
• Integrated Keycloak authentication and third-party login validation across portals.
• Built a RabbitMQ-based email service and MinIO file storage for a medical data platform.
• Implemented document import/export and data transformation for an employee loyalty portal.