Denys S.

Helping startups and growing companies launch polished, scalable products - fast. ⚡️𝐒𝐞𝐫𝐯𝐢𝐜𝐞𝐬 𝐭𝐡𝐚𝐭 𝐈 𝐨𝐟𝐟𝐞𝐫 𝗦𝗮𝗮𝗦 𝗣𝗿𝗼𝗱𝘂𝗰𝘁 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗺𝗲𝗻𝘁 As a Full Stack Developer, I build complete SaaS platforms, not just features. I handle user authentication, subscription billing with Stripe, admin dashboards, usage tracking, multi-tenant architecture, and role-based access control - building clean systems that scale with your user base. 𝗙𝘂𝗹𝗹-𝗖𝘆𝗰𝗹𝗲 𝗦𝗼𝗳𝘁𝘄𝗮𝗿𝗲 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗺𝗲𝗻𝘁 As a Full Stack Developer and Mobile Developer, I handle the entire lifecycle of your React Native, React, or Next.js project from the first prototype to post-launch updates. I make sure the product stays stable, secure, and user-friendly across all web and mobile platforms. 𝗠𝗩𝗣 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗺𝗲𝗻𝘁 As a Full Stack Developer, I help startups ship fast but solid. I’ve launched multiple MVPs from scratch that helped founders validate their ideas, pitch investors, and scale on top of clean architecture, quick iterations, and strong technical foundations. 𝗠𝗼𝗯𝗶𝗹𝗲 & 𝗪𝗲𝗯 𝗨𝗜 𝗜𝗺𝗽𝗹𝗲𝗺𝗲𝗻𝘁𝗮𝘁𝗶𝗼𝗻 As a Mobile Developer and Full Stack Developer, I deliver pixel-perfect Figma-to-code implementation. I build sharp, responsive UIs with smooth animations and clean interactions, maintaining a strict mobile-first engineering approach. 𝗪𝗲𝗯𝘀𝗶𝘁𝗲𝘀 & 𝗟𝗮𝗻𝗱𝗶𝗻𝗴 𝗣𝗮𝗴𝗲𝘀 As a Full Stack Developer, I build high-converting landing pages, marketing websites, Shopify storefronts, and custom company pages. Using React, Next.js, Tailwind CSS, or simple static stacks, I deliver SEO-optimized, blazing-fast, and easy-to-manage web properties. 𝗕𝗮𝗰𝗸𝗲𝗻𝗱 & 𝗔𝗣𝗜 𝗗𝗲𝘃𝗲𝗹𝗼𝗽𝗺𝗲𝗻𝘁 As a Full Stack Developer, I engineer solid, scalable backends built with Node.js, NestJS, or Express, backed by PostgreSQL or MongoDB databases. I design clean REST/GraphQL APIs, implement robust authentication, and integrate third-party services like Stripe, Firebase, and OpenAI. 𝗔𝗜 𝗜𝗻𝘁𝗲𝗴𝗿𝗮𝘁𝗶𝗼𝗻 As a Full Stack Developer, I integrate OpenAI and other LLM APIs into real production products, not just demos. I build practical AI features, custom chatbots, smart recommendation engines, prompt engineering workflows, and RAG pipelines. 𝗢𝗻𝗴𝗼𝗶𝗻𝗴 𝗦𝘂𝗽𝗽𝗼𝗿𝘁 & 𝗠𝗮𝗶𝗻𝘁𝗲𝗻𝗮𝗻𝗰𝗲 As a Full Stack Developer, I stick around after launch to fix bugs, optimize performance, and scale your product as your business requirements evolve and user base grows. 🌟 𝐂𝐥𝐢𝐞𝐧𝐭 𝐒𝐮𝐜𝐜𝐞𝐬𝐬 𝐒𝐭𝐨𝐫𝐢𝐞𝐬: Denys is a great contractor - very capable and eager to get the job done properly. He communicates well and is knowledgeable - ⭐⭐⭐⭐⭐ I can honestly recommend Denys as developer and the most responsible, proactive freelancer I’ve ever met. Quick answers and responses, step by step demo calls, fair price, strong skillset, fluent English - ⭐⭐⭐⭐⭐ Denys is an absolutely phenomenal engineer. I say this as someone who worked with him project to project over many years as a supervisor and then eventually a co-worker. Hands down the best Upwork hire I've had!!! - ⭐⭐⭐⭐⭐ 𝗪𝗵𝘆 𝘄𝗼𝗿𝗸 𝘄𝗶𝘁𝗵 𝗺𝗲? I own projects - not just code tasks. I think like a founder - not just a dev. I deliver fast, communicate clearly, and stick to timelines. I’m in this for the long term, not one-off jobs. 📩 Send me a message or invite - happy to jump on a quick call and see if I'm a good fit for your project. SaaS Development, SaaS Product Development, B2B SaaS, B2C SaaS, Subscription Platform Development, Multi-Tenant Architecture, MVP Development, Startup Development, Rapid Prototyping, Product-Market Fit, Full-Cycle Software Development, End-to-End App Development, Mobile App Development, iOS App Development, Android App Development, React Native App Development, Flutter App Development, Cross-Platform App Development, Hybrid App Development, Mobile App Design, Mobile App UX/UI Design, App Performance Optimization, App Scalability, Web Development, React, Next.js, Tailwind CSS, Landing Page Development, Shopify Development, SEO Optimization, Backend Development, Node.js, Nest.js, Express.js, RESTful API, GraphQL API, PostgreSQL, MongoDB, Database Design, API Integration, Third-Party Integrations, Authentication & Authorization, Role-Based Access Control, Stripe Integration, Payment Integration, Subscription Billing, Firebase Integration, Firebase Cloud Firestore, Firebase Cloud Messaging, Push Notifications, AWS, AWS Mobile Services, Cloud Architecture, Serverless Architecture, AI Integration, OpenAI API, LLM Integration, Prompt Engineering, Conversational AI, Chatbot Development, Recommendation Systems, RAG (Retrieval-Augmented Generation), TypeScript, JavaScript, Feature Integration, App Maintenance, Ongoing Support, Bug Fixing, Software Development Life Cycle, Agile Development, Git, GitHub, CI/CD Updated November 2026