Marcin Kowalski

I’m a Senior Software Engineer with 8+ years of experience developing backend systems using Node.js, TypeScript, and SQL-based databases. I focus on payment integrations, API development, and event-driven services that work reliably in high-volume environments.

I’ve built and evolved business payments and banking platform capabilities, including payout management, currency exchange operations, and payment reconciliation. I’ve implemented REST API endpoints and microservices, and I’m comfortable owning features from design through production release while collaborating closely with frontend, QA, and product teams.

My work is strongly grounded in performance and operations: I optimized PostgreSQL schema/query performance to reduce transaction query latency by 18% during peak usage. I also reduced deployment rollback incidents by 15% through improved CI validation and staging verification, and cut SQL execution time by 22% through targeted query improvements.

I’m at my best in remote, cross-functional engineering settings—pairing event-driven integrations (Kafka/RabbitMQ/SQS) with cloud infrastructure on AWS. I contribute to secure development practices using OAuth2/JWT and OWASP fundamentals, and I support delivery with automated testing (Jest, Vitest, Cypress) and CI/CD automation (GitHub Actions, GitLab pipelines, Terraform).