Senior full-stack developer building complete products — web, mobile, backend, and infrastructure. I've shipped production systems serving 10,000+ users at 99.9% uptime, APIs handling 10M+ requests/day, and real-time platforms with 1,000+ concurrent connections. What I build: 🔹 Marketplaces & on-demand platforms — booking, payments, GPS tracking, in-app messaging, admin dashboards 🔹 SaaS platforms — authentication, subscriptions, admin panels, analytics, role-based access, user management 🔹 Mobile apps (iOS / Android / React Native) — with backend APIs, push notifications, in-app purchases, offline sync, app store deployment 🔹 Real-time systems — WebRTC, video/voice calling, live chat, WebSocket infrastructure at scale Recent work: Duurs — on-demand services marketplace built from scratch (web + mobile). Real-time booking, GPS tracking, in-app messaging, secure payments, admin dashboards. I'm the lead full-stack developer. Enterprise VoIP platform — 1,000+ concurrent calls, HD video, AI-powered IVR, 99.9% uptime Small business platforms — Zomg The Handyman, Southbaypilatesandme, and others — full websites with booking, admin, and payment integration Stack: Node.js, Python, TypeScript, React, Next.js, React Native, Swift, Kotlin, PostgreSQL, Redis, MongoDB, Docker, Kubernetes, AWS, GCP, Firebase. How I work: ✅ Clear scope before we start — no surprises mid-project ✅ Honest timelines, with early flags if something turns out harder than estimated ✅ Clean, documented code you or your team can maintain ✅ Direct communication — I respond within a few hours during business hours Based in California (PST), flexible globally. Military veteran. Master's in Computer Science (CSUN). Message me with your project and I'll come back with a real scope — not a pitch.

Senior software developer with 8+ years of experience building real-world products across iOS, front end, back end, and automation, with a strong focus on using AI to deliver faster, higher-quality code. By combining a deep understanding of core programming concepts with advanced AI-assisted workflows, development time is reduced while keeping code maintainable and easy to hand off. What you get • Clean, well-structured code built by someone who understands architecture, not just syntax, and can work comfortably across multiple languages and stacks. • AI-accelerated implementation that still respects best practices, so you get the speed of rapid prototyping without sacrificing reliability or readability. • Clear, direct communication, with frequent check-ins, progress updates, and a focus on aligning technical decisions with your business goals. AI-accelerated development For every project, AI tools are used as force multipliers, not crutches. Because core concepts like object-oriented design, data structures, and modular architecture are well understood, prompts can be written in a precise, technical way that produces higher-quality code suggestions instead of generic boilerplate. This allows rapid switching between languages and frameworks while still keeping a consistent level of quality and performance. Tech background • 8+ years of professional programming experience, including shipping and maintaining production applications. • Hands-on work in iOS (Swift), scripting/automation, and general software development using tools like Git for collaborative workflows. • Experience acting as a “full-stack problem solver,” moving between front end, back end, and infrastructure to get things done instead of being blocked by rigid role boundaries. How projects are handled • Start by clarifying requirements, constraints, and success criteria so the solution fits your actual use case, not a generic template. • Use AI to explore options, generate scaffolding, and refactor code, then manually review, test, and refine to ensure correctness and maintainability. • Communicate in plain, non-jargony language while still being technically precise, making it easy for both technical and non-technical stakeholders to understand tradeoffs and next steps. If you need a developer who understands how to blend solid engineering fundamentals with modern AI tooling to ship faster without cutting corners, this is exactly the kind of work taken on.

Top 1%; part of the UpWork's Expert-Vetted program. ✅More than 100 completed projects on UpWork 🇺🇸Available for calls during business hours 🎓4 AWS Certifications: Professional Solutions Architect (result is 945 out of 1000), Professional DevOps Engineer (915), Machine Learning Specialty, Cloud Practitioner In short, the solutions I created are used by millions of users every day. I could build a web, mobile or desktop application using Serverless Computing, conforming to the principle of the least privilege under version control for each function (Pay-per-use AWS or Google Cloud infrastructure that scales indefinitely). When I code either the Frontend or Backend solutions, the experience I have defined the prioritization of the characteristics for the product: 1. Simplicity (readability). ---- all frontend services I create are event-driven with the FaaS infrastructure or in rare cases BaaS. ---- I write in strict TypeScript (if you don't know TypeScript, it is the same JavaScript plus type safety to increase stability). 2. Technical scalability ---- Comparing to containerized microservices, where parts are connected to each other, FaaS development allows to create completely independent functions. It is easier to manage and to make changes as you split the functionality into much smaller blocks. ---- FaaS can scale indefinitely, so any load the cloud provider (such as AWS) could handle is supported. -------- If you have 0 customers today, your bill is $0, comparing to microservices, where you have to have at least one container running $25/month. A typical project is eight containers. -------- If you have a billion customers tomorrow, FaaS auto scales horizontally to handle the new load automatically, with the pricing of an optimized solution close to $2-5/million requests for ALL infrastructure combined. 3. Size ---- The size of the bundled assets needs to be small as it affects the operating costs (you are charged by millisecond). ---- I have created tens of different custom Webpack solutions for all types of possible cases to minimize and optimize the bundles, including code splitting, tree shaking, finding the most appropriate target for the JavaScript (or TypeScript transpilation), image minification and lazy-loading (PNG, JPEG, SVG, etc), service workers, manifest, etc. -------- and even the updating process of the objects in a file hosting (such as AWS S3) to upload only those assets that have changed. -------- I have worked on many projects, every time trying to find something else to improve, so the solutions are extremely well optimized. 4. Performance ---- when I had projects to optimize for performance, I have created a lot of custom solutions as public solutions are for everyone and, therefore, typically suboptimal for a particular case. I create SPAs, conforming to PWA standards, and frontend plugins using React.js. I follow Component Driven Development (CDD) together with Visual Test Driven Development. For that, I use PlayWright and Storybook. When writing styles, I use CSS-in-JS (primarily using Emotion library). The Desktop app development involves also Electron, but the overall process is the same. That is the reason why it is easy to convert my solutions to distribute as a desktop app. When creating mobile apps, I use either React Native or create hybrid web-based solutions with Capacitor.js. 🔒Backend: I am a strong proponent of Serverless Computing, who has extensive experience with FaaS and BaaS, automatically generating IAM rules and cloud services, and conforming to the principle of the least privilege for each function/service. In regards to HTTP APIs, I create: - RESTful APIs covering them in tests and preparing for adoption by frontend devs via password-protected documentation over web endpoints where the frontend devs are able to observe and interact with Swagger UI that conforms to the OpenAPI 3.0 specification. - GraphQL. Created in all possible ways: custom with plain GraphQL library (no Apollo or other wrappers), with Apollo; in Programmatic and Declarative ways I automate provisioning of infrastructure (IaC) using AWS CDK and Google Deployment Manager configs, so that it takes one CLI command to create the defined as code cloud infrastructure. Project management/Tracking I am used to daily reporting and knowing that communication is the key, I constantly try to improve clients' experience. I know best methods in version control and I conform to them, doing PRs, releases, keeping multiple branches, and using stashes. ---- I have automated branching & PR requests, as well as connected bots for notifying about changes in corporate chats.The code I write goes through automatic code-styling processing that improves readability and overall quality of the provided work. I use: ESLint and Prettier for all automated code formatting needs. Respectfully, Olzhas

Web3 Developer | Smart Contracts | dApps | Crypto | Tokenomics | Bots I’m Donatas, a 𝗕𝗹𝗼𝗰𝗸𝗰𝗵𝗮𝗶𝗻 𝗱𝗲𝘃𝗲𝗹𝗼𝗽𝗲𝗿 with expertise in 𝗯𝗹𝗼𝗰𝗸𝗰𝗵𝗮𝗶𝗻 𝗱𝗲𝘃𝗲𝗹𝗼𝗽𝗺𝗲𝗻𝘁, 𝘀𝗺𝗮𝗿𝘁 𝗰𝗼𝗻𝘁𝗿𝗮𝗰𝘁𝘀, 𝗱𝗔𝗽𝗽𝘀, 𝘁𝗼𝗸𝗲𝗻𝗼𝗺𝗶𝗰𝘀, etc.. I help businesses and startups design, build, and scale their Web3 projects from idea to launch. 🔹 What I Do Best: ✅ ICO/IDO/IEO/IZO ✅ NFT as well as Crypto Minting ✅Exchange Development ✅Crypto Wallet Development ✅NFT Auction/Store/Minting/Marketplace/Design Development ✅Cross-chain Development ✅Pure Blockchain Development ✅Blockchain Gamification Development Apart from that. I am an also Expert at: | Android | iOS | Angular | MEAN Stack | Python | Laravel | Codeigniter | NodeJS | ExpressJS | MongoDB | React JS | Objective C | SWIFT | IONIC | Xamarin | React Native | WordPress | 🔹 Why Work With me? ✔ 𝗭𝗲𝗿𝗼 𝗥𝗶𝘀𝗸 𝗚𝘂𝗮𝗿𝗮𝗻𝘁𝗲𝗲 - If you don’t love working with me after 2 weeks, no matter how much work I’ve done, I’ll walk away - no payment required. ✔ 𝗙𝗿𝗲𝗲 𝗦𝘂𝗽𝗽𝗼𝗿𝘁 - We will provide support for 2 months post contract for any questions for free ✔ Already proven results with actual names. My latest work: 🟢 Litas – All-in-one Web3 ecosystem: multi-chain CEX, wallet, tokenomics, and full-stack product design. 🟢 BotanixLabs – BTC-reward wallet platform with EVM & Bitcoin auth, fair games, NFT gating, and auto payouts. 🟢 Zuvu – Decentralized AI governance with staker voting, upgradeable ERC-20, and modular architecture. 🟢 Mothership Bots – Launchpad bot suite: escrow, token launch, airdrops, and treasury control across EVM & Solana. Let’s build the future of blockchain together! Reach out, and let’s discuss your project.

Expert-Vetted on Upwork (Top 1% of security professionals). If you're building on the cloud and want to find the security gaps attackers would exploit — before they do — I can help. I’m a cybersecurity consultant and founder of Exfiltra, helping startups and enterprises secure their applications, cloud infrastructure, and DevOps pipelines. I have worked with organizations generating $6B+ in annual revenue and helped companies strengthen security across cloud environments, applications, and compliance programs. I personally lead security engagements and, when needed, bring in specialists from my team at Exfiltra to support larger or complex projects. Most clients hire me when they want to: ✔ Secure Azure / AWS / GCP environments ✔ Perform professional penetration testing ✔ Implement DevSecOps and secure CI/CD pipelines ✔ Prepare for SOC 2, ISO 27001, HIPAA, FedRAMP, or CMMC ✔ Improve security posture using industry frameworks CORE EXPERTISE AZURE & CLOUD SECURITY • Azure security architecture reviews • Microsoft Defender for Cloud & Sentinel • Identity security (Entra ID / Conditional Access) • Cloud configuration reviews and CIS Benchmark hardening APPLICATION SECURITY & PENETRATION TESTING • Web application penetration testing • API security testing • Mobile application security testing • Network and cloud penetration testing • Assessments aligned with OWASP Top 10 and OWASP ASVS DEVSECOPS & SECURITY AUTOMATION • Secure CI/CD pipelines (Azure DevOps / GitHub Actions) • Infrastructure as Code security (Terraform / Bicep) • SAST and DAST integration in pipelines SECURITY TOOLS • Snyk • Semgrep • OWASP ZAP • Burp Suite • Wazuh • CrowdStrike • Microsoft Sentinel AI & LLM SECURITY • AI application threat modeling • Prompt injection and model abuse testing • Secure architecture for AI-powered applications WHY CLIENTS WORK WITH ME • Upwork Expert-Vetted (Top 1% of freelancers) • Founder of Exfiltra – a cybersecurity services company • Supported by a team of security specialists for larger engagements • Contributor to OWASP ZAP • Experience securing environments for organizations generating $6B+ in revenue • Background in both software engineering and cybersecurity • Security research involving organizations like the U.S. Department of Defense NOT A GOOD FIT IF • You want to hack or recover social media accounts • You want enterprise-grade security but are not willing to invest in it If your goal is to build secure systems instead of reacting to breaches later, feel free to invite me to your job or send a message describing your project.

12+ years building software for JPMorgan Chase, Cisco, Avaya, and Ford. 12,400+ hours on Upwork alone. AI-augmented engineer running parallel agents with Claude Code and Codex. Production-grade output at a pace that would normally require a team. Built ML-powered palm biometrics kiosk apps for Keyo (Series A, $30M+ raised, thousands of devices deployed, backed by Netflix co-founder), deployed at JPMorgan Chase. Shipped AI-driven identity verification SDKs at Journey.ai (Gartner Cool Vendor, Zero Knowledge Network, multi-modal biometrics with 99.9999% accuracy) used by Cisco Webex and Avaya, and on prototypes for unreleased Ford partnerships. Worked on an AI teaching assistant active in 125+ UK classrooms, 40,000+ questions answered by AI. Led the development of the POV Disposable Camera Android app (3M+ users, 4.9 stars). AI feature integration (OpenAI, Anthropic, Azure), web applications (Next.js, TypeScript), full-stack products with Firebase, Supabase, and Cloud Functions, Kotlin Multiplatform apps, app refactoring and modernization, native Android and AndroidTV apps (Kotlin, Jetpack Compose), IoT and kiosk applications, and video streaming solutions (ExoPlayer, HLS). Software engineer building mobile apps, web apps, and backend systems. Engineering Manager and CTO experience. Delivering multiple times faster than traditional development without sacrificing code quality or architecture. "Excellent development manager. Writes clean code, good eye for design, successfully managing a team of mobile developers. A core manager in our organisation." - Chris Cooper, CEO at NeoMatrix "Takes initiative and drives the product forward, not only through technical skills but understanding the what and the why of what we're building." - Todd Zusman, Director of Engineering at Journey.ai "Strong technical skills, excellent communication, a true team player and great manager. Architect of a complex cross-platform project. We'd happily work with him again." - Cayetana Polanco, CPO at Keyo "A rare find and very dedicated engineer, team lead and manager. Thiago always delivers." - Al Calendario, Director of Integration at Keyo "Accomplished all tasks very well, sometimes beyond expectations. In command of the Android API, managed tasks with little supervision, keen interest in the business purposes of the app." - Stephen Hosking, CEO at NoPowerTXT "Communication is impeccable, incredibly reliable, very detail-oriented. The kind of leader who grows through adversity and never loses sight of the people." - Lynda Yang, SHRM-SCP at Untitled Shows Kotlin, Java, TypeScript, Python Jetpack Compose, MVVM/MVI, Hilt, Room, Retrofit, Coroutines, ExoPlayer Kotlin Multiplatform Firebase (Firestore, Cloud Functions, RTDB), Node.js, Next.js Claude Code, Codex, OpenAI API, Anthropic API, Azure AI GitHub Actions CI/CD, automated code review, multi-worktree workflows PostHog, Crashlytics, Sentry Check the portfolio below and send a message. Happy to discuss your project.

26 years in engineering. 15 years in Enterprise Architecture. 10+ years in Fintech. My clients: Revolut, Experian, Baird & Co, London Fish Exchange, and the Church of England. You can partner with me for: FINTECH GENERAL: Digital Banking | Payments | Wallets & Ledgers | Crypto-Fiat | OTC & Institutional Crypto | Core Banking Engine | Personal Finance | Card Management | Payment Gateways. OPERATIONS & ERP: Custom ERP | Internal Platforms | Inventory Management | Back Office | Admin Portals | Excel-to-Platform Transformation | Vault Management. TRADING: Trading Platforms | FIX API | Transaction Engine. BACKEND: Backend-heavy Fintech | Complex Logic | RBAC | High-load Systems | Performance Optimization. COMPLIANCE: KYC / KYB | AML | FinCrime | Compliance | Technical Due Diligence | SEC Data Analysis | LegalTech. AI: AI Agents | RAG Pipelines. STRATEGY & ARCHITECTURE: Fractional CTO | Solution Architecture | Technical Roadmap | Legacy System Rebuilt | MVP Development | Technology Assessment. TECH STACK: C# / .Net | JavaScript | Node.js | Python | Angular | Next.js | React | React Native | AWS/Azure/GCP | MSSQL / PostgreSQL / Aurora. I'm always up for new challenges! Let's build something amazing together!

High expertise in iOS development, specially on tackling complex problems. Focus on "done is better than perfect", always making the best tradeoffs between effort and value. With my management experience, I can either coordinate long-term projects with larger teams or take on short-term tasks to achieve quick wins. I'm also strong in troubleshooting and navigating unknown codebases, which is helpful to figure out issues with existing apps or simply adding new features.

5+ Years Building Production-Grade Apps Real Startup Experience & Have worked with 30+ Startups Cloud-Deployed, Scalable, AI-Powered Invite me to your project or message me. Accepting new projects. Senior Full Stack Developer | Next.js, React Expert | AI Integration | Production Apps | Full Stack Development --- What I Deliver: 1️⃣ Full-Stack Applications - Next.js, Supabase, Firebase, React, TypeScript, PostgreSQL. Production apps with real users, cloud-deployed and scaling. 2️⃣ Backend Architecture - NodeJS, ExpressJS, NestJS, PostgreSQL, Supabase, Firebase, Microservices, RESTful APIs, GraphQL, real-time systems. Serverless and serverfull. 3️⃣ AI Integration - AI-accelerated development with Claude, Cursor, Gemini. LLM integration, chatbots. 4️⃣ SaaS Platforms - Cloud-native apps with auth, Stripe payments, LemonSqueezy Payments, Mollie Payments, Posthog - Google analytics, monitoring. AWS, Vercel, Railway, Firebase, AWS Lighthouse, hetzner deployments. --- I build production-ready applications that handle real users, real traffic, and real business constraints.
 I’ve built and scaled high-traffic event websites handling 200,000+ monthly visitors and 4,000+ transactions per month, as well as fully-functional SaaS products for startups that are actively generating MRR today. As a founder, I take products from zero to hero; owning architecture, infrastructure, and execution end-to-end. I combine enterprise-level engineering discipline with startup execution speed, delivering battle-tested systems designed to scale. --- Why Work With Me: ✨ AI-Accelerated Development - Claude, Cursor, Gemini workflows delivering 4-5x faster without sacrificing quality 🎯 Production-First - Error handling, monitoring, security, scaling from day one ⚡ Full-Stack Mastery - Database to APIs to UI/UX—complete ownership 🔧 Cloud-Native - Serverless or serverfull, architected for 99.9% uptime 📊 Real World Experience - Systems handling thousands of concurrent users in production --- Tech Stack: Frontend: React, Next.js 14+, 15+, 16+ React Native, TypeScript, Tailwind CSS, shadcn/ui Backend: NestJS, Node.js, Express, WebSocket Database: PostgreSQL, Supabase, Firebase, Prisma, Redis, MySQL, Vector DBs Infrastructure: AWS, Vercel, Netlifty, Railway, Docker, Serverless, CI/CD AI: Claude API, OpenAI, Gemini, LangChain, Claude
Payment: Stripe, LemonSqueezy, Mollie integrations --- Results: ✅ Apps with 99.9% uptime handling thousands of users ✅ 60-80% faster delivery via AI-accelerated development ✅ Scalable cloud architectures (serverless/serverfull) ✅ AI features creating competitive advantages ✅ Production code with tests, docs, monitoring --- Best For: ✔️ Startups building scalable production MVPs ✔️ Founders needing technical co-founder expertise ✔️ AI integration into existing products ✔️ Real-time, cloud-native applications ✔️ Teams valuing quality and speed ✔️ Integrating payment solutions --- 𝗜𝗻𝘃𝗶𝘁𝗲 𝗺𝗲 𝗼𝗿 𝗺𝗲𝘀𝘀𝗮𝗴𝗲 𝗺𝗲. 𝗥𝗲𝗮𝗱𝘆 𝘁𝗼 𝗯𝘂𝗶𝗹𝗱. Uğur Kellecioğlu | Full-Stack Developer | AI Integration | Production Apps | SaaS | AI --- *Keywords:* 🔸 Full Stack Developer - Next.js Developer - NestJS Developer - TypeScript Developer - Node.js Developer - React Developer - JavaScript Developer - Frontend Developer - Backend Developer 🔸 React Native Developer - Mobile App Development - iOS Developer - Android Developer - Cross-Platform Development 🔸 API Development - REST API - GraphQL API - Microservices - Backend Architecture - Server-Side Development 🔸 PostgreSQL Developer - Database Developer - Supabase Developer - Firebase Developer - Database Design - SQL - Prisma - TypeORM 🔸 AI Developer - AI Integration - LLM Integration - Claude API - ChatGPT Integration - OpenAI Developer - Gemini Integration - Machine Learning Developer 🔸 Chatbot Developer - Chatbot Development - AI Chatbot - Conversational AI - Customer Service Bot - Chat Application 🔸 Cloud Developer - AWS Developer - Serverless Developer - Lambda Developer - Cloud Architecture - DevOps Engineer - CI/CD 🔸 SaaS Developer - SaaS Development - Web Application Developer - Stripe Integration - Mollie Integration - LemonSqueezy Integration - Payment Gateway - Subscription Platform 🔸 Real-Time Developer - WebSocket Developer - Socket io - Live Chat - Real-Time Application - Event-Driven Architecture 🔸 Startup CTO - Technical Co-Founder - MVP Development - Product Development - Tech Lead - Engineering Manager 🔸 tRPC - Zustand - React Query - TanStack - Tailwind CSS - shadcn/ui - Fastify - Docker - Kubernetes

From Idea to Scalable Startup – Fast! Bringing a startup to life requires speed, flexibility, and the right technology. As a Certified Bubble.io Developer, I specialize in turning startup ideas into fully functional web and mobile apps—without the high costs and delays of traditional development. 🔹 Why Work with Me? Startups need more than just an app—they need a scalable product that grows with their business. I’ve helped founders build, launch, and iterate fast using Bubble.io, ensuring they validate their ideas, attract investors, and scale seamlessly. ✔ MVP Development – Get your Minimum Viable Product built in weeks, not months. ✔ Scalable Architectures – Design apps that handle thousands of users without breaking. ✔ No-Code Meets AI & APIs – Integrate OpenAI, Stripe, Zapier, Google, and more. ✔ Investor-Ready Dashboards – Track metrics, automate workflows, and impress stakeholders. ✔ Growth-Focused UI/UX – Optimize for engagement, conversions, and retention. ✔ Lean & Agile Process – Iterate quickly based on real user feedback. 📈 Startups I’ve Helped: SaaS Platforms – Subscription-based web apps built for growth. Marketplaces – Connecting buyers & sellers with frictionless transactions. Social & Community Apps – Scalable social platforms with real-time engagement. Internal Business Tools – Custom solutions for businesses & entrepreneurs. 💡 My Process: 1️⃣ Idea Validation & Planning – Clarifying features, defining user flows, and setting up a roadmap. 2️⃣ MVP Development – Building a functional prototype for user & investor feedback. 3️⃣ Scalability Optimization – Structuring databases, workflows & APIs for long-term growth. 4️⃣ Testing & Launch – Ensuring a smooth, bug-free user experience. 📌 Ready to turn your startup vision into reality? Send me a message so we can schedule a time to meet!