Petteri Tolonen enhanced backend systems for Opetushallitus, focusing on both the ataru and kouta-backend repositories. He delivered advanced application search features, enabling flexible queries by SSN, applicant OID, and whitespace-tolerant name matching, which improved data retrieval accuracy for application reviewers. In kouta-backend, Petteri migrated testing infrastructure from MockServer to WireMock, enriched API documentation, and improved validation logic to support athletic vocational training cases. His work involved Scala, SQL, and integration testing, emphasizing maintainability through code cleanup and configuration management. Over two months, Petteri’s contributions deepened backend reliability and data integrity, addressing real-world requirements without introducing regressions.