Daniil

Daniil Sapielkin
Team Lead / Software Developer / Front-End Developer
Links: [відкрити контакти](див. вище в блоці «контактна інформація») · LinkedIn · GitHub · Medium · @qwe1rtyy

S U M M A RY

Software Developer with 6+ years building production-grade, product-driven applications within cross-functional teams. Strong in scalable frontend
architectures, complex business logic, and large-scale state management, with deep experience in Web3 and smart-contract integrations. Own features
end-to-end — from technical design and risk assessment through production and long-term support — with a focus on performance, reliability, and predictable
UX. Combines hands-on execution with team-lead qualities — mentoring engineers, driving architectural decisions, and coordinating team priorities with
analysts, product, and project managers.

CORE SKILLS

Languages TypeScript, JavaScript (ES5, ES6+)

Frontend React (Hooks, Class Components), Next.js (SSG/ISR), Redux (Thunk/Saga), Zustand, Sanity (Headless CMS), Telegram
Mini Apps, react-hook-form, zod

Web3 wagmi, viem, ethers.js, web3.js, WalletConnect, MetaMask SDK, Web3Modal, wallet integration, multichain (ERC-20 / ERC-
721), smart-contract interaction

API & Real-time GraphQL, REST, WebSocket

Testing Jest, React Testing Library

UI & Data Grids Material UI, Ant Design (AntD), Radix UI, AG Grid, Storybook, styled-components, SASS/SCSS, CSS Modules, StyleX, Lit

Architecture Feature-Sliced Design, OOP, SOLID, DRY/KISS, domain-driven design, large-scale state modeling

Performance & Delivery Lighthouse, CI/CD (Vercel), preview environments, release flow management, Agile (Scrum/Kanban)

AI-assisted dev Cursor, Claude, GitHub Copilot

EXPERIENCE

Software Engineer (Contract) — Ivy Tech · Apr 2026 – Jul 2026 · Remote
▸ Designed the content architecture (Sanity headless CMS + Next.js SSG/ISR), letting non-devs ship content changes safely without redeploys.
▸ Built and shipped production front-end features in React, Next.js, and TypeScript within a cross-functional team.
▸ Collaborated with backend and design on reliable API integration and consistent UX.

Front-End Developer — TheOne · Jan 2025 – Feb 2026 · Remote
▸ Built and shipped the frontend of a Telegram Mini App and a companion web app that extended its functionality, within a cross-functional team.
▸ Developed and maintained a scalable Feature-Sliced Design (FSD) frontend architecture.
▸ Engineered domain-level custom React hooks and reusable UI components to encapsulate business logic.
▸ Took part in technical planning, identifying architectural risks early, and partnered with backend and design on stable API integration.
▸ Participated in architectural decision-making, collaborating with analysts, product managers, and project managers on requirements and roadmap.
▸ Contributed to sprint planning and retrospectives, helping prioritize upcoming tasks within the team.

Front-End Developer — Boosty Labs · Mar 2024 – Jan 2025 · Remote
WalletConnect
▸ Integrated Solana support into WalletConnect, enabling secure cross-chain wallet interactions, and optimized core frontend modules.
▸ Built and published a Sign-In With Solana (SIWS) npm package to a private registry.
SafeLite
▸ Engineered the frontend of a decentralized asset management app (Safe{wallet}-style) in Next.js, with client-side smart-contract interaction.
▸ Hardened ERC-20 transaction flows for security and reliability; validated contract behavior on a BuildBear forked-mainnet sandbox and public testnets.
▸ Collaborated with blockchain engineers on correct handling of contract calls, signatures, and edge cases.
Front-End Developer — CODY · Mar 2023 – Feb 2024 · Remote
▸ Designed and built from scratch a cross-platform Web3 authentication npm library (Lit + JavaScript with a React-based architecture for shared logic),
usable from React, Angular, Vue, and vanilla JS.
▸ Architected a reusable wallet-abstraction layer (single global class) integrating MetaMask, WalletConnect, Ledger, and seed-phrase wallets, so support
for any new wallet could be added with minimal code.
▸ Owned technical architecture, semantic versioning, documentation, and public npm distribution end-to-end.
▸ Implemented interaction with multiple smart contracts and optimized multi-contract on-chain calls (batching reads to cut RPC round-trips) for token-
exchange functionality; aligned with a Solidity developer on contract behavior.

Front-End Developer — 3PLCRM (CRM) · Jul 2022 – Mar 2023 · Remote
Credit Card CRM System
▸ Built CRM features for monitoring customer credit-card activity: balance tracking, plan-based access control, and automated card-blocking.
▸ Developed multi-channel top-up flows (cash, card, internal transfers) and plan-driven adaptive UI.
▸ Structured scalable frontend components and documented them in Storybook.

Warehouse Management CRM
▸ Extended a warehouse management system with new modules: goods receipt, shipment scheduling, invoice correction, and document printing.
▸ Built reporting dashboards for inventory, shipments, and operational KPIs, improving reusable component design.

Front-End Developer — MeGaDev OÜ · Jan 2022 – Jul 2022 · Remote
▸ Built internal HR and performance-management systems: performance tracking, automated time-off accrual, and payroll calculation.
▸ Developed analytics dashboards for team performance and operational insight.
▸ Integrated Web3 functionality (smart-contract interaction via viem) into a Next.js app.
▸ Reviewed Solidity contract logic from the frontend side and collaborated on system design and delivery.

Front-End Developer — CustomerCRM (Upwork client) · Nov 2020 – Dec 2021 · Remote
▸ Built an internal management system for team leadership and customer oversight, within a cross-functional team.
▸ Developed a custom platform combining Jira-like task management, Excel-style data tables, and team performance tracking.
▸ Implemented complex, data-driven UIs for monitoring team progress, workloads, and operational metrics.
▸ Developed features in React with Ant Design, extended with a large set of custom reusable components, and contributed to code reviews.

OPEN SOURCE & WRITING

Hexora — Open-source Web3 Security SDK · Jan 2026 – Present
hexora.site · github.com/DaniilSapielkin01/Hexora · npmjs.com/package/hexora
▸ Solo-built and published a Web3 security SDK for wallets and dApps that detects address poisoning, phishing domains, and malicious transactions
locally and offline, in three function calls.
▸ Shipped as a TypeScript monorepo across 6 EVM chains (Ethereum, BNB Chain, Polygon, Avalanche, Arbitrum, Optimism); live on npm (v2.0.0, MIT).
▸ Technical writing on Medium — Web3 frontend & architecture.

SOFT SKILLS

Mentored team members · Designed scalable frontend architecture · Worked directly with clients · Estimated project timelines & resources · Participated
in Agile (planning, grooming, demos) · Presented results through demos · Collaborated with designers & backend teams · Led architectural decision-making ·
Coordinated with analysts, product & project managers · Prioritized team tasks & backlog · Facilitated retrospectives

LANGUAGES

English — Upper-Intermediate (B2) · proficiency working