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in Croatia

I build React and Next.js products that make complex workflows easier to use. My work includes analytics dashboards, financial onboarding, chat interfaces and Everfur's mobile app, which I built solo through launch. I've worked professionally as a frontend developer since 2018. Some of the work I've owned: • Everfur: Built the React Native and Expo mobile app solo and took it through launch. I also built React and Shopify Hydrogen web interfaces and an embeddable chat SDK. • Hurree: Led frontend development of an analytics and reporting dashboard from scratch, including the dashboard UX, data visualization and component architecture. • Fulfilled Financial: Built multi-step onboarding and financial-planning flows, handling branching paths, validation and integration with backend services. • Siteline: Handled the complete website redesign and implementation, established a consistent visual theme across pages, and migrated the site to Astro with full server-side rendering and substantial SEO work. • Skriba: Sole frontend developer for a work-reference management product built with Next.js and Tailwind CSS. My core stack is React, Next.js, TypeScript and Tailwind CSS. I can take ownership of a product frontend, implement a redesign, or work with your team on a defined feature, including the product and design decisions needed to make it work well. I'm based in Croatia and available to start immediately.

I am a Software Developer with a Bachelor's degree in Business Informatics from the Faculty of Organization and Informatics, University of Zagreb. My primary focus is backend and application development for web, mobile, and software platforms. I have experience building applications using technologies such as Node.js, TypeScript, C#, .NET, Kotlin, SQL databases, and REST APIs. I develop web applications, backend systems, mobile applications, and software tools while focusing on clean architecture, maintainable code, and reliable application logic. My development background allows me to understand both the technical implementation and the user experience side of software products. In addition to development, I also provide manual QA testing and usability validation for web and mobile applications. Because of my technical background, I approach testing from a developer’s perspective and can identify not only visible UI bugs but also potential logic issues, backend problems, or API-related errors. My QA work includes: • Mobile app testing (Android / iOS) • Web application testing • AI conversational system testing • Functional and usability testing • Writing detailed bug reports with reproduction steps • Verifying bug fixes and validating application flows I regularly collaborate with development teams and create structured issues using tools such as GitHub Issues, Jira, Trello, Notion, and Slack. I am familiar with modern development workflows including GitFlow methodology, which allows me to communicate issues clearly and efficiently with engineers. Technical stack: • Node.js / Express • C# / .NET • Kotlin (Android development) • SQL databases • NoSQL databases (MongoDB) – schema design, querying and integration with backend APIs • REST APIs • Git / GitHub Alongside development and QA work, I am also open to smaller or quick tasks such as bug verification, app testing, usability testing, and technical support tasks. I am reliable, detail-oriented, and focused on delivering accurate and high-quality results. If you need a developer who understands both software development and quality assurance, I would be happy to help.

Hi, I'm Dario, a software engineer from Zagreb, Croatia, with an MSc in Software Engineering and almost a decade of experience working with software, data, testing, and digital products. My work sits at the intersection of technology, quality, language, and AI. I help clients evaluate whether software, content, translations, and AI-generated outputs are actually correct, usable, and consistent. ### What I currently do **QA & Software Testing** • Web and mobile application testing • Functional, regression, UI and cross-platform testing • Bug identification, reproduction and detailed reporting • API and integration testing • Test-case creation and quality review • Code and implementation review from a QA perspective **AI Evaluation & Data Work** • Evaluating AI-generated responses and technical content • Prompt and response review • Data annotation and labeling • Checking AI outputs for accuracy, consistency, relevance and instruction-following • Technical evaluation of software/code generated or assisted by AI tools **Translation & Localization** • Croatian / Bosnian / Serbian ↔ English • Technical and software-related translation • UI and product localization • Translation QA and proofreading • Terminology and consistency review • Checking whether translated content sounds natural and appropriate for its context **Technical Review & Software Engineering** • Code reviews and technical audits • Frontend and full-stack development • Vue.js, React.js, TypeScript and Python • FastAPI, Flask, Node.js and PostgreSQL • Understanding existing codebases and identifying practical improvements My software-engineering background is important because I don't approach these tasks only from a language or testing perspective. When I review a product, translation, AI response, or piece of code, I can also understand the technical context behind it. I regularly use modern AI-assisted development tools in my workflow, but I always verify the result myself. The goal is not simply to produce output faster, it's to make sure the final result is accurate, reliable and fit for the actual use case. I'm particularly interested in long-term or recurring work involving QA, AI evaluation, software testing, technical translation/localization, code review, and related technology projects. If you need someone who can understand both the technical details and the end-user context, I'd be happy to take a look at your project.

Need a full-stack product built fast without sacrificing scalability? With 15 years as a Full-Stack Developer and AI Engineer, I’ve delivered 16k+ hours and $1M+ earnings across web and mobile products. For startups and SaaS teams, I build React, Next.js, Node.js, and Flutter solutions that launch cleanly and scale confidently. 🎯 HOW I CAN HELP YOU FULL-STACK WEB APPLICATION DEVELOPMENT Launch scalable web products that convert users faster and support long-term growth. I build React, Next.js, Node.js, and TypeScript applications with architecture choices that have supported $1M+ in Upwork earnings and 100% Job Success. AI AGENT AND OPENAI INTEGRATION Add intelligent features that automate work, reduce manual effort, and create new product value. I integrate OpenAI APIs and AI workflows into existing platforms to accelerate delivery and turn ideas into usable AI-powered products. MOBILE APP DEVELOPMENT Ship iOS and Android apps that give users a smooth experience across devices and help you reach more customers. I develop with Flutter, React Native, Swift, and Kotlin, with proven experience delivering apps published to both Apple and Google app stores. SAAS PLATFORM DEVELOPMENT Turn complex ideas into secure, scalable SaaS products that are ready to monetize. I have built multi-tenant platforms with authentication, billing, APIs, and dashboards for startups and enterprise teams in as little as MVP timelines. API AND BACKEND ENGINEERING Increase system stability, speed up integrations, and support growth with robust backend foundations. I design Node.js, NestJS, Express, PostgreSQL, and cloud-based systems that handle real-world product demands across web, mobile, and AI features. 🏆 RESULTS "Thanks to Cinnamon's efforts, the app's server response times were excellent, and the end client was thrilled with the results. The team was responsive and pragmatic in responding to needs, communicating via virtual meetings, emails, and messages. Their talented engineering team was impressive." – Gregory W., Founder, Mojave Interactive LLC "Thanks to Cinnamon's work, the client has seen a 25% higher completion rate and 40% less completion time. The pricing calculators have reduced the error rates by 50%. The team delivers timely items, responds quickly to messages, and addresses requests effectively. Their support is unique." – Premnath M., Head of Software Development Digital Bank, BAWAG AG "The Android app has thousands of downloads and impressive online ratings, which reflects Cinnamon Agency's technical expertise. The team is willing to work long hours to meet deadlines. They excel at project management and have a robust reporting system in place." – Garin Toren., Founder, Ping 🎖 JavaScript Algorithms and Data Structures Certification 🎖 React Developer Certification 🎖 AI Engineering and LLM Integration Certification See full case studies in my portfolio below. 🤝 𝗚𝗘𝗧 𝗜𝗡 𝗧𝗢𝗨𝗖𝗛 Have an app idea or product to launch? Message me on Upwork today for a free consultation and a clear plan to move forward. I typically respond within 4 hours and can offer quick turnaround for urgent projects. 𝗛𝗼𝘄 𝗜 𝗪𝗼𝗿𝗸 I build in React, Next.js, and TypeScript to ship fast, maintainable web apps, then use Node.js, PostgreSQL, and AWS to keep the backend reliable and scalable. For AI features, I integrate OpenAI APIs and Cursor into workflows that automate tasks and add real product value. I also use Flutter when a project needs a polished cross-platform mobile app. I build full-stack web applications with React and Next.js, integrate Node.js APIs, and deliver mobile app development with Flutter and AI development that scales.