Andrii Kryzhanivskyi

Profile

achievements

• Built over 15 web projects:from CRM systems and high-load applications to responsive landing pages with backend integration, email services and third-party APIs.

• Democratization of specialized knowledge:Designed the application and coded my own narrow-field expertise into its logic, making complex tasks at the level of laboratory head/candidate of science accessible to users without special training

• Implemented frontend-backend integration:in more than 10 projects using modern technologies: Node.js, NestJS, MongoDB, PostgreSQL, RTK Query. Ensured secure data exchange, fast client-server interaction, and real-time synchronization.

• Authorization implementation:Implemented an authorization system (JWT, Redux, email verification) and role-based access control in more than 8 products, ensuring data protection and privacy.

• CRUD operations:Built a full cycle of CRUD operations for data management (users, contacts, products, orders, recipes) — for a total of 12+ solutions and applications.

• UI interfaces:Created scalable and adaptive UI interfaces for different types of users, using modern libraries (React, Next.js, TypeScript, Material-UI), implemented themes, drag-and-drop, interactive widgets (weather, date, timers, music player).

• Business logic:Developed complex business logic for beauty, agro, e-commerce and military sectors (CRM “Mriya”, AgroLabTest, Shop, Booking, CMS), migrated legacy projects to a modern stack (React→Next.js+TS), optimized the operation of systems with a large number of concurrent users.

• Performance optimization:Optimized performance and loading time, implemented SSR, SSG, advanced routing, image processing automation, minimized project size (e.g., from 60GB to 8GB in Shop).

• Feature integrations:Implemented email automation, notifications, subscriptions, and PDF generation in many solutions.

• UI/UX solutions:Ensured adaptability and retina optimization in all UI/UX solutions, understanding the importance of mobile experience (especially for beauty and e-commerce).

• FHEVM dApps deployment:Built and deployed 30+ privacy‑preserving dApps on Zama FHEVM, covering healthcare, HR, engineering analytics, gaming and subscription use cases.

• Confidential smart contracts:Designed and implemented confidential smart contracts using Solidity, FHEVM types (euint) and homomorphic operations on Sepolia/FHEVM testnet.

• Encrypted client flows:Integrated Relayer SDK and Ethers v6 into lightweight frontends (vanilla JS) for encrypted client–contract interactions and KMS‑based decryption flows.

My Codewars level

Faq

• Tell about yourself or what did you do at your last job?

  I am a developer with over 3 years of experience in creating web applications and integrating them with backend systems. I am currently working as a Full stack Developer in a RepitoCRM, I worked on four major projects: Shop, AgroLabTest, Confidential military system - CMS and Booking.

  In the Shop project:

  • - Optimized 70,000+ product images achieving 90% disk space savings: reduced average file size from ~700KB to ~20-60KB through WebP conversion and adaptive compression

  • - Improved image load times 10-15x through intelligent on-demand loading with specified parameters

  • - Implemented a reliable data processing system (Excel → PostgreSQL) with validation, normalization and synchronization of products

  In AgroLabTest:

  • - Designed the application and coded my own narrow-field expertise into its logic, making complex tasks at the level of laboratory head/candidate of science accessible to users without special training

  • - 3-level nested data structure (experiment → samples → days) with automatic activity calculations in real-time.

  • - 60% time reduction on data processing through automation of complete workflow (registration → reporting)

  • - Centralized data repository with analytics replacing scattered documents (Word, Excel, Google Drive).

  • - Role-based access control (admin/worker/viewer) ensuring data security and workflow integrity.

  I made my greatest contribution to the CMS project, a military application with integrated mapping and routing.

  • - Developed a REST API for building routes in real time, implemented complex data aggregation in MongoDB (grouping, filtering, query optimization) and correctly configured dependencies in NestJS.

  • - Integrated the Leaflet library to build a map displaying routes and markers, implemented custom map selection (OpenStreetMap) and dynamic route display.

  • - Eliminated infinite requests, logic duplication, and issues with displaying icons on the map. This increased system stability and reduced the load on the frontend.

  • - Implemented specialized display of target icons on the map – calculation of direction of movement, rotation of icons based on position.

  • - Created a scalable frontend base structure (React + SCSS Modules), organized the directory hierarchy, implemented barrel imports, and configured global styles, which prepared the project for further development.

  • - Implemented specialized display of target icons on the map – calculation of direction of movement, rotation of icons based on position.

  • - Configured Redux Toolkit + Persist, moved work with targets to a centralized state, refactored useTargetsStorage for specialized route handling logic, which simplified maintenance and made the system more predictable.

  • - Created modal windows for user settings (notifications, goal update parameters), integrated map base selection (OSM), added tools for working with the map (zooming, ruler, fullscreen).

  • - Transferred the business logic from the frontend to the backend (NestJS + MongoDB), reducing the load on the browser and increasing system performance.

  For Booking:

  • - I implemented a multi-level permission system for two types of users with conditional rendering, dynamic navigation, state synchronization between components, and adaptive logic depending on the role (Client/Business).

  • - Built a stable state management ecosystem based on Redux Toolkit with async thunks, a centralized store, and protected routes with dynamic access to routes according to user role.

  • - Ensured a seamless user experience through automatic session saving, refresh token handling, intuitive navigation, and separation of authentication scenarios for business and customers.

  • - Designed a production-ready REST API (10+ endpoints) with dependency injection, custom middleware, centralized error handling, and full support for role-based access control at the request level.

  • - Created flexible and secure MongoDB schemas with bidirectional relationships, compound indexes for query optimization, Mongoose validators for data integrity checks, and implemented JWT middleware with role-based access control.

  Thus, at RepitoCRM, I developed my experience in complex B2B solutions, data optimization and cartography integration and at CMS, I consolidated my expertise in military tech, cartography, performance optimization and the development of highly reliable products for critical users.

  At my previous job at Beauty Sync, I developed a CRM system for a beauty salon, optimized business processes, and created adaptive landing pages for a barbershop, integrating complex logic for managing staff, customers, services, and bookings. I migrated the code base to a modern stack (Next.js, TypeScript), ensured efficient real-time data exchange between the frontend and backend, and actively collaborated with business experts and designers in the beauty industry.

  Before that, I worked as a freelancer and successfully implemented more than 10 projects (4 of them full stack), including 6 landing pages and 8 web applications. In these projects, I developed adaptive and interactive interfaces, implemented complex functionality, including backend development and database integration.

  When working on projects, I actively use modern tools and frameworks (React.js, Next.js, TypeScript, Node.js, Nest.js, Tailwind CSS, Material-UI) to optimize performance, improve UX/UI and ensure high quality code. Collaborated with designers, backend developers, and testers to synchronize processes and achieve business goals.

• What are your main strengths?

  Technical expertise: I have in-depth knowledge of modern technologies, React, Redux, Next.js, Node.js, MongoDB, and Express. While working on the Mriya-CRM project, I developed the main functionality for managing employees, customers, services, and goods. He was responsible for designing key modules, performance optimization, and integration. As a result, he reduced page loading time by 35-55% and increased system performance by 25-45%. Also provided a user-friendly and intuitive interface that significantly improved the user experience.

  Adaptability and improvement: While working on Mriya-CRM, we modernized the technology stack, replacing React and JavaScript with Next.js, TypeScript, and Material-UI. This allowed him to increase frontend performance by 43% thanks to SSR, reduce the number of errors due to the use of typing, and speed up component creation by 25% thanks to Material-UI standards. Despite having no previous experience with these technologies, I quickly mastered them by adapting components and implementing optimizations.

  Teamwork: In the project, Mriya-CRM successfully coordinated the work of a team that included front- and back-end developers, designers, testers, and a project manager. He regularly held brainstorming sessions where the team discussed ideas and found optimal solutions. He also maintained constant communication with clients to clarify requirements and quickly adapt to changes. Thanks to this, he ensured clear synchronization between departments, high quality of the product and completion of tasks on time.

• Do you actually work with Web3 and blockchain, or are you mainly a traditional full‑stack developer?

  Yes — Web3 is a core part of what I do now, especially around privacy‑preserving dApps and Zama’s FHEVM (Fully Homomorphic Encryption for EVM), not just a side experiment. Over the last months I’ve been building a portfolio of 30+ decentralized applications on top of Zama’s FHEVM protocol as part of the C4 decentralized builders collective, within a developer bounty program focused on on‑chain privacy and confidential computing. These are not token launchpads or meme projects — they are confidential applications where smart contracts process encrypted data directly on‑chain.

  A few examples:

  • - Private Donor Match – a medical dApp for private matching of blood/organ donors and recipients. Blood type, Rh factor and HLA score are encrypted end‑to‑end; the smart contract still computes compatibility (match / no match) on‑chain without ever seeing those values in plaintext.

  • - Anonymous Review Analytics – an internal tool for engineering teams. Developers submit encrypted 1–5 scores for code reviews; managers only see aggregated quality levels (0 = excellent, 1 = ok, 2 = needs attention), never raw scores per person.

  • - Other prototypes – confidential subscriptions, private scoring, encrypted analytics, and gamified flows that all rely on operating over encrypted integers (euint*) using FHEVM operations such as FHE.eq, FHE.ge, FHE.and, FHE.select.

  In these projects, my role is full‑stack Web3 rather than a narrow “Solidity‑only” or “frontend‑only” position:

  • - On the smart contract side, I design and implement contracts on FHEVM using specialized encrypted types (euint8, euint16, ebool) and homomorphic operations, and I encode programmable privacy directly into the contract: what stays encrypted, what can be publicly decrypted, and who is allowed to trigger decryption via KMS flows. I work with patterns like FHE.allow, FHE.allowThis, encrypted access control, and bytes32 handles for public decryption.

  • - On the frontend side, I build lightweight UIs (React or vanilla HTML/JS) that connect via MetaMask and Ethers.js v6, and integrate Zama’s Relayer SDK so that all sensitive data is encrypted in the browser before it ever touches the blockchain. The contract only receives encrypted handles and attestations rather than raw user input.

  • - From an end‑to‑end perspective, I take projects from idea → data model and UX → smart contract implementation → FHEVM/Sepolia deployment → frontend integration → testing of the full encryption/decryption flow with the Zama KMS. This includes debugging edge cases, thinking about UX around cryptography, and documenting patterns so they can be reused across multiple dApps.

  To make this sustainable, I also designed a reusable FHEVM dApp template: a small architecture that combines a Solidity FHEVM contract, Relayer SDK wiring, and a minimal UI. This template became the foundation for more than 30 prototypes across different domains, which helped me focus on business logic and privacy models instead of re‑solving the same boilerplate every time.

  All of this builds on top of my traditional full‑stack background (React/Next.js, Node.js/NestJS, Python/PostgreSQL, MongoDB, REST APIs), so I don’t just ship isolated contracts — I ship complete applications: UI, wallet flows, contract logic, and integration with existing web tooling. That mix of Web2 and Web3 experience is especially important in the FHEVM space, where you need to care about performance, UX, and cryptography at the same time.

Portfolio