Harel Mazor contributed to the puppeteer/puppeteer and maplibre/maplibre-tile-spec repositories, focusing on robust test coverage and modern TypeScript workflows. He implemented a WebGL context creation test in TypeScript to validate browser graphics reliability, configuring CI environments for consistent results. In maplibre-tile-spec, Harel modernized the release process by migrating to a TypeScript-first build, simplified dependencies to reduce bundle size, and enhanced the geometry API with polygon support and improved type safety. His work involved JavaScript, Node.js, and CI/CD tools, demonstrating depth in code organization, testing, and release engineering to improve maintainability and reliability across both projects.