John Kapantzakis

Open-source, real-time observability platform. Frontend of Netdata Cloud, a large, data-intensive React application.

• Built frontend capabilities for Netdata's AI assistant, evolving it from a basic chat interface to persistent LLM conversations powered by Netdata-specific tools and investigation workflows. Also implemented frontend support for Model Context Protocol (MCP), allowing users to connect external tooling.
• Optimized data processing and React rendering to improve performance and eliminate unnecessary remounts.
• Cut reported frontend CI runtime by about 60% through Jest test sharding and test-reliability fixes.
• Built the foundational Dynamic Configurations UI and continued evolving it to support complex, dynamically generated configuration forms, using the react-jsonschema-form library.
• Helped build end-to-end AI Insights investigation reports (generation, rendering, scheduling) and contributed to enterprise identity features: SCIM, SSO, role and room mappings, and label-driven room membership.

Job search engine used by 15M+ jobseekers a month across 20 countries.

• Built Labour Market Intelligence, a new data product, from zero to launch in under a year on Next.js, in a team of three (one product manager, two developers).
• Built the product's interactive charts and maps with Apache ECharts, visualising hiring demand, salaries and trends across regions.
• Shipped search, grouping and filtering by location, sector, salary and other dimensions, so users could explore labour-market data for multiple countries.

One of Greece's leading e-commerce marketplaces. Partners department: tooling for merchants.

• Developed and maintained the merchant platform (orders, payments, daily operations) with Ruby on Rails and Hotwire Turbo server rendering, using React for selected views.
• Contributed two features to Hotwire Turbo that shipped in Turbo 7 and were credited in the release announcement: the turbo:frame-render event and target elements on fetch events.
• Published two articles on the Skroutz engineering blog, on progressive data loading in React and lazy loading with Hotwire.

Greek business-software company. Epsilon ESS, an employee self-service web platform on ASP.NET and C#.

• Progressed from junior web designer to full-stack developer responsible for the product's frontend, implementing features end to end from C# backend to TypeScript frontend.
• Introduced TypeScript, webpack and Redux-managed asynchronous views into a legacy ASP.NET Web Forms frontend, and added unit tests on both sides (Mocha and Chai, xUnit).
• Built a Node.js and Handlebars CLI that generates the boilerplate for a new form: the ASP.NET user control and async handler, the TypeScript page script and Redux state, and the C# data models.

Family business: a live Greek e-shop for handmade baby and toddler clothes. A WordPress/WooCommerce monolith split into a Next.js storefront and a headless WooCommerce backend.

• Moved the product catalogue to a Next.js 16 App Router storefront on Vercel. Kept checkout, payments and accounts on WordPress behind an API subdomain, restyled to match the new UI.
• Carried the cart across both apps through a server-side proxy to the CoCart API, with a cart-key handoff to WooCommerce checkout.
• Cut product API payloads from ~2.4 MB to ~400 KB so they fit the Next.js data cache. Added indexable category routes, a live sitemap and Product/Breadcrumb structured data.