Jakub Kowalski

Led development of customer-facing spend management workflows using React and TypeScript, implementing feature-flagged releases and progressive rollouts under financial compliance constraints, reducing incident rate on new launches by 40%. Defined API contracts and schema evolution strategies in Node.js and PostgreSQL to enable safe parallel frontend/backend development and shorten cycle time by 25%. Introduced structured logging and OpenTelemetry tracing across critical payment flows, improving incident triage speed and reducing MTTR by 35%. Optimized high-traffic dashboards with code-splitting, memoization, and query optimization, improving time-to-interactive by 30% while preserving auditability. Strengthened CI/CD with automated Playwright end-to-end tests and safer database migration patterns, decreasing rollback frequency and improving deployment confidence.

Built and maintained mandate setup and exception-handling interfaces in React and TypeScript, integrating RESTful APIs under regulatory constraints, increasing successful mandate completion rates by 18%. Redesigned backend services in Node.js to support event-driven correctness with idempotent handlers and Kafka-based workflows, reducing reconciliation inconsistencies and support escalations. Implemented controlled data migrations with backfills and shadow reads during schema evolution, ensuring zero-downtime releases across high-volume payment systems. Collaborated with product and design to translate complex compliance requirements into clear UX flows, reducing user errors while preserving backend reliability. Improved observability through structured logging and SLO definition for critical APIs, decreasing operational noise and improving cross-team incident coordination.

Developed responsive patient booking and clinic management interfaces in React, translating wireframes into accessible, high-performance UI components used across multiple European markets. Designed RESTful backend services in Node.js and PostgreSQL to support scheduling workflows with strong consistency, reducing double-booking incidents by 22%. Introduced API versioning and contract-first integration to support distributed frontend teams, minimizing breaking changes and improving release predictability. Improved frontend performance through lazy loading and bundle optimization, enhancing mobile usability on low-bandwidth networks. Established shared testing templates and CI practices, increasing automated coverage and reducing regression defects in critical booking flows.