Sergii K.

Hi, I’m a senior TOP PLUS engineer specializing in codebase takeover, security hardening, and production engineering. I step in when an application works in a demo, but real traffic, live payments, and actual users start exposing critical flaws underneath. Whether your application was built by a previous dev team, an agency, or AI tools like Cursor, Lovable, Replit, Bolt, or Claude, I take direct ownership of your existing system-stabilizing and scaling your software without forcing an expensive, unnecessary rewrite. WHAT I DO Codebase Takeover & Stabilization Architecture review, critical user-flow testing and a clear technical triage of what needs attention first. Security & Data Protection Authentication, authorization, Supabase RLS, API security, secrets, permissions, payment flows and sensitive-data exposure. Performance & Reliability Database bottlenecks, N+1 queries, inefficient APIs, slow application flows and production failures — measured before and after. Production Hardening Error handling, validation, monitoring, deployment and the engineering foundations required for reliable operation. Feature Development New functionality added without destabilizing existing business-critical workflows, with testing around authentication, payments and data access. HOW I WORK Audit → Prioritize → Stabilize → Improve I first understand the architecture and critical business flows, then provide a clear technical assessment with priorities and effort. From there, I fix the highest-impact issues in controlled, reviewable changes - without unnecessary rewrites. TECH STACK Java · Next.js · React · TypeScript · Node.js · Supabase · PostgreSQL · RLS · Python/FastAPI · Stripe · REST APIs · AWS · Vercel · Docker · Playwright · Vitest · GitHub Actions Have an existing application that needs to become secure, reliable, and enterprise-ready? Send a short overview of your current tech stack and the bottlenecks you are experiencing for an immediate architectural assessment and an actionable path forward.