Publication
Responsive Web Design Media Query Examples Explained
https://www.toptal.com/developers/css/introduction-to-responsive-web-design-pseudo-elements-media-queries
Tomislav is available for hire
Hire TomislavTomislav Krnic
Verified Expert in Engineering
Startups Developer
Ghent, Belgium
Toptal member since October 12, 2012
Bio
Tomislav is an AI-driven product engineer, senior full-stack developer, and 8x founder with 20+ years of experience building SaaS, mobile, and web platforms. He has delivered 150+ products, from lean MVPs to enterprise-scale systems, with two successful exits and multiple awards. Combining hands-on engineering with product and architecture leadership, Tomislav helps teams turn AI-generated prototypes into scalable, production-ready software with measurable business impact.
Portfolio
Mealmate via Krnic CommV
AI Agents, AI Copilots, Artificial Intelligence (AI), AI Automation...
Roko via Krnic CommV
AI Automation, AI Copilots, AI Agents, Next.js, Firebase, Supabase, Stripe...
CityX via Krnic CommV
Firebase, React Native, iOS, Android, React, APIs, Card Payments, Payment APIs...
Experience
- Startups - 20 years
- User Interface (UI) - 20 years
- Full-stack - 15 years
- React - 9 years
- Firebase - 8 years
- React Native - 7 years
- Mobile Applications - 7 years
- ChatGPT - 2 years
Preferred Environment
React Native, Full-stack, React, Web Development, Node.js, APIs, AI Automation, AI Consulting, AI Copilots, AI Agents
The most amazing...
...thing was turning an idea into a production-ready, AI-native platform in two weeks, with real operations, payments, and scale-first architecture from day one.
Work Experience
Founder | CTO | Full-stack Product Engineer
2026 - PRESENT
Mealmate via Krnic CommV
- Built an AI-native food ordering platform from zero to a market-ready product in just two weeks, combining product strategy, architecture, and hands-on delivery.
- Architected the full ecosystem across consumer mobile app, business app, CMS, web surfaces, and Firebase back end as one coherent product platform.
- Implemented core commerce flows for restaurant discovery, menus, customization, ordering, payments, and operational workflows needed for real-world rollout.
- Used AI-assisted development workflows to compress build cycles dramatically while still maintaining production-grade structure, validation, and release discipline.
- Designed a multi-environment setup across mobile, web, CMS, and back-end services, enabling fast iteration on staging without compromising production safety.
- Led the product end-to-end as founder-CTO, translating business direction into shipped features, technical decisions, and a scalable execution model.
Technologies: AI Agents, AI Copilots, Artificial Intelligence (AI), AI Automation, React Native, TypeScript, Stripe API, Stripe, Node.js, Next.js, OpenAI API, Mapbox API, Redux Toolkit, MUI CSS, New Products, Mobile Development, User Interface (UI), User Experience (UX), CMS, Vercel, Analytics, Software Architecture, AI-assisted Development, AI-generated Code, Claude Code
Founder | Full-stack Engineer
2026 - PRESENT
Roko via Krnic CommV
- Architected an AI pipeline that auto-generates launch-ready websites in under 60 seconds from new business-registration signals.
- Built a multi-tenant SaaS platform with an automated acquisition engine, market intelligence, and partner/admin dashboards.
- Designed and shipped a full monorepo from zero to production as sole engineer using Next.js, Firebase, Supabase, and Stripe.
- Automated go-to-market workflows covering outreach, onboarding, and conversion without manual intervention.
- Integrated AI content generation pipelines producing localized, SEO-ready copy across all tenant sites automatically.
- Integrated a live database of nearly two million Belgian businesses, ingesting new daily registrations automatically as acquisition signals.
- Built an automated enrichment pipeline that researches each new company's competitors, market position, and industry context without manual input.
- Engineered a daily outreach system delivering personalized welcome emails with competitive intelligence to newly registered businesses at scale.
- Designed the full acquisition loop — from signal detection to site generation, enrichment, and outreach — as a zero-touch automated operation.
Technologies: AI Automation, AI Copilots, AI Agents, Next.js, Firebase, Supabase, Stripe, Stripe API, TypeScript, Multi-tenant SaaS, React, React Flow, APIs, API Design, Software Architecture, AI-assisted Development, AI-generated Code, Claude Code
Founder | Product Architect | CTO
2019 - PRESENT
CityX via Krnic CommV
- Built CityX as a unified smart city platform that consolidates core municipal and citizen services into one scalable app ecosystem.
- Architected the product as a modular SaaS system, enabling cities to activate only the services they need and expand over time.
- Defined and shipped a multi-surface platform including a citizen mobile app, a city dashboard, a partner integration layer, and an analytics foundation.
- Positioned CityX for international rollout with multilingual support and deployment model optimized for go-live timelines measured in weeks.
- Developed the platform vision around open ecosystem principles, where service providers integrate once and scale across multiple city deployments.
- Led product direction and technical execution toward a long-term objective: becoming a core digital infrastructure layer for European smart cities.
Technologies: Firebase, React Native, iOS, Android, React, APIs, Card Payments, Payment APIs, Node.js, Mobile Design, User Interface (UI), User Experience (UX), Full-stack, UI Design, Google Cloud Platform (GCP), Mobile Development, Startups, Web & Mobile Applications, Cross-platform, Front-end Development, Mobile UI, Mobile UX, Mobile, Push Notifications, REST APIs, TypeScript, Live Chat, Mobile Applications, ChatGPT, Full-stack Development, Artificial Intelligence (AI), OpenAI, App UI, App UX, UX Design, Azure, API Design, GitHub, Apps, App Design, Technical Leadership, NoSQL, App Store, Google Play Store, Leadership, Architecture, Web Scraping, AI Automation, OpenAI API, Python, Maps, JSON, Redux, Express.js, Cloud Firestore, Google Maps API, Mobile Apps, AI Chatbots, Git, Large Language Models (LLMs), API Integration, Expo, Front-end, Next.js, Tailwind CSS, React-JSS, Canvas, Generative Artificial Intelligence (GenAI), WhatsApp API, RESTFul APIs, Web App Deployment, Pixel Perfect, Application State Management, Cross-platform App Development, Software Architecture, AI-assisted Development, AI-generated Code, Claude Code
Senior Full-stack Engineer
2026 - 2026
Attorney Client Connect
- Worked with Attorney Client Connect, a US legal marketplace connecting clients with bar-verified attorneys for paid phone/video consultations and retainers. Built end-to-end on Next.js, React, TypeScript, Supabase, and Vercel.
- Integrated multiple production systems: Stripe (Connect lead-billing + subscriptions), Confido Legal (trust/retainer payments), Twilio (masked click-to-call + SMS), and LLM/AI for content-blind reply drafting and case intake.
- Assured US-specific depth: 50-state + DC coverage, county-level (FIPS) search, state-bar verification, recipient-timezone-correct notifications, and idempotent payment billing verified end-to-end in real browsers before every release.
Technologies: JavaScript, Ionic, iOS, Node.js, Next.js, Vercel, TypeScript, PostgreSQL, Twilio API, Android, Video Calling, Payment APIs, Role-based Access Control (RBAC), Supabase, Live Chat, Authentication, Authorization, REST APIs, React, Dashboards, Software Architecture, AI-assisted Development, AI-generated Code, Claude Code
Full-stack/React Native Developer
2025 - 2026
Journey Rewards Inc.
- Led React Native mobile app delivery from product requirements to production-ready architecture in a venture-backed startup environment.
- Built core mobile flows and engineering foundations for a startup that secured an $8M seed round.
- Defined scalable front-end structure that supported rapid iteration, stable releases, and continuous product growth.
- Translated early-stage product ambiguity into shipped features, technical direction, and consistent execution cadence.
- Collaborated with leadership and product stakeholders to align engineering delivery with key business and funding milestones.
Technologies: React Native, Mobile Development, REST APIs, SQL, Node.js, TypeScript, Amazon S3 (AWS S3), React, RESTFul APIs, Full-stack Development, Software Architecture, AI-assisted Development, AI-generated Code, Claude Code
Lead Full-stack Engineer
2025 - 2026
Loop Africa
- Took Loop Africa from a raw early-stage concept to a fully defined product, owning the translation of user intent into end-to-end architecture, platform design, and delivery execution.
- Led development of a multi-platform fitness ecosystem across a React Native mobile app, three Next.js web apps, and approximately 50 Firebase Cloud Functions.
- Designed and implemented core commercial and operational capabilities, including subscriptions, payments, QR check-ins, partner workflows, and admin tooling.
- Drove launch execution that achieved strong early traction, with 5,000+ fitness events processed and 80+ partner venues onboarded within the first 30 days.
- Built scalable technical foundations and release discipline that enabled rapid iteration, reliable operations, and continued product expansion after launch.
Technologies: React Native, JavaScript, React, Full-stack, AI Agents, AI Automation, AI Copilots, AI Consulting, TypeScript, Node.js, Next.js, Firebase, REST APIs, Software Architecture, Mobile Development, User Interface (UI), User Experience (UX), Full-stack Development, AI-generated Code
Lead Full-stack Product Engineer
2024 - 2025
OBVS, INC
- Built the product end-to-end from initial idea to launched mobile app, web store, CMS, and Firebase back end.
- Collaborated directly with the founder to turn product vision into shipped features, technical decisions, and launch-ready execution.
- Developed a commerce system covering store sales management, product operations, automated emails, location-based features, and multiple payment flows.
- Architected both the customer-facing app and web store as one connected product ecosystem backed by a shared admin and back-end platform.
- Supported rapid product growth by delivering a high-traffic eCommerce experience optimized for conversion and repeat customer usage.
- Helped scale the platform to thousands of active users and loyal customers through a polished buying experience and reliable product delivery.
- Built a curated digital commerce experience around certified products, contributing to strong customer feedback and sustained product traction.
Technologies: Mobile Development, Full-stack, Minimum Viable Product (MVP), Technical Leadership, iOS, React Native, Mapbox, NoSQL, Software Architecture
Senior Native React Developer | Mobile App Prototype Engineer
2023 - 2024
Bird Buddy, Inc.
- Built a mobile prototype for an AI-powered consumer product at a startup that raised $8.5M and scaled into a large global user community.
- Prototyped core app journeys for a platform with a 300,000-member community, focusing on intuitive onboarding and content-first engagement.
- Created reusable mobile UI patterns that enabled fast product iteration and quick validation of feature hypotheses with stakeholders.
- Aligned prototype decisions with the product’s public pillars: AI-assisted species recognition, educational profiles, and intuitive app navigation.
- Validated cross-platform behavior and interaction quality on iOS and Android to reduce implementation risk for later production phases.
- Collaborated directly with the founder on product direction, translating strategic goals into a mobile prototype and actionable implementation decisions.
Technologies: React Native, Figma, User Experience (UX), User Interface (UI), iOS, Android, Mobile, UI Design, UX Design, Cross-platform, Cross-platform App Development, APIs, UI Development, User Experience Design, Software Architecture
Full-stack Mobile Developer
2020 - 2022
Entrio
- Developed a mobile app from Entrio, the most prominent Croatian event-ticketing company with over 1,200 events per year and over 280,000 tickets.
- Built a React Native application from scratch that was intended as a ticket scanner connected to a few servers with non-SQL and SQL databases.
- Contributed to developing the React Native application that consisted of multiple solutions, including communication between scanners, offline mode, and tons of logs. Event organizers could hire Entrio to ensure a smooth process.
- Entrio ticketing for the 2025 Zagreb Hippodrome event, recognized as the world’s top ticketed concert, with 504,000 tickets sold.
Technologies: React Native, UI Design, UX Design, Firebase, Firebase Realtime Database, APIs, Scanning, Ticketing, Ticket Systems, Events, Event Ticketing, SQL, SQLite, Amazon Web Services (AWS), Google Cloud Platform (GCP), Figma, Mobile Development, Front-end Development, Mobile App Development, Mobile UI, Mobile UX, Mobile, Push Notifications, REST APIs, TypeScript, Cross-platform, Mobile Applications, Full-stack Development, PostgreSQL, API Design, GitHub, Apps, App Design, Technical Leadership, NoSQL, App Store, Google Play Store, Leadership, Architecture, JSON, Redux, Cloud Firestore, Mobile Apps, Git, API Integration, Front-end, Next.js, RESTFul APIs, Web App Deployment, Pixel Perfect, Application State Management, Cross-platform App Development, Software Architecture
Co-founder | CTO and Full-stack Mobile Developer
2018 - 2020
Grga
- Worked on Grga, a mobile application for payment and ordering processes related to restaurants and bars. The app provides a solution for connecting to more than 50,000 cash registers. One solution enables users to make orders and pay with a QR code.
- Designed a system, created a mobile app and the UI/UX and connected with the payment gateway. Worked on it for a little over two years; millions were paid without any mistakes or wrong orders, and I have a reason to be satisfied with the project.
- Completed the project and after a successful exit, Grga still exists within a large multinational company.
Technologies: Firebase, React Native, CSS, iOS, Android, Payment APIs, Credit Card Processing, User Interface (UI), User Experience (UX), Full-stack, UI Design, Amazon Web Services (AWS), Google Cloud Platform (GCP), Mobile Development, Startups, Front-end Development, Mobile App Development, Mobile UI, Mobile UX, Mobile, Push Notifications, REST APIs, TypeScript, Cross-platform, Mobile Applications, Full-stack Development, PostgreSQL, API Design, GitHub, Apps, App Design, Technical Leadership, NoSQL, App Store, Google Play Store, Leadership, Architecture, JSON, Redux, Cloud Firestore, Mobile Apps, Git, API Integration, Front-end, Next.js, RESTFul APIs, Web App Deployment, Pixel Perfect, Application State Management, Cross-platform App Development, Software Architecture
Experience
Daydeck - AI-first macOS App
https://daydeck.krnic.beI conceived, designed, and built Daydeck end-to-end as the sole developer: a native macOS app that turns the desktop wallpaper into a live timeline of the user's projects. I ran development AI-first. I set the architecture, wrote the specs, and reviewed every change, while several Claude Code agents worked in parallel on the Swift, JavaScript, and Node.js code. This let me take the product from idea to the Mac App Store on my own and ship four releases in three months, localized into seven languages.
I built the app as a Swift/AppKit shell hosting a WKWebView interface, with StoreKit in-app purchases, sandboxing, and a hardened runtime. I also made the product AI-native: I wrote an MCP server, a Claude Code plugin, and a custom URL scheme so that AI assistants can read and edit a user's plan while the app reloads it live. Finally, I automated releases through the App Store Connect API and set up AI agents that handle growth research and directory submissions.
I built the app as a Swift/AppKit shell hosting a WKWebView interface, with StoreKit in-app purchases, sandboxing, and a hardened runtime. I also made the product AI-native: I wrote an MCP server, a Claude Code plugin, and a custom URL scheme so that AI assistants can read and edit a user's plan while the app reloads it live. Finally, I automated releases through the App Store Connect API and set up AI agents that handle growth research and directory submissions.
QuizMonster - Kids' Learning App Run as an AI Self-driving Company
https://www.krnic.be/projects/quizmonsterQuizMonster is a kids' learning app (ages 6–12, web, iOS, and Android) that turns a photographed book page into a spoken quiz hosted by animated monster characters, with every question grounded in a verbatim quote from the source. I founded it as an "AI Self-Driving Company": not only is the code written with AI, every function of the business is designed to be carried out by AI agents, with one person setting direction and approving what ships.
Build: I act as architect, specifying and verifying while coding agents implement the Expo/React Native app, the design system, and a Python pipeline that generates character animation (models, alpha matting, HEVC/VP9 encoding).
Market: agents produce and iterate landing pages, store listings, videos, and campaigns.
Sell: pricing, funnels, and conversion loops run as agent experiments, with me owning the numbers.
Care and Run: an assistant supports parents and teachers; monitoring, content, and releases run through agents behind human approval. QuizMonster is the live template for the AI-native operating model I help companies adopt. Launching November 2026.
Build: I act as architect, specifying and verifying while coding agents implement the Expo/React Native app, the design system, and a Python pipeline that generates character animation (models, alpha matting, HEVC/VP9 encoding).
Market: agents produce and iterate landing pages, store listings, videos, and campaigns.
Sell: pricing, funnels, and conversion loops run as agent experiments, with me owning the numbers.
Care and Run: an assistant supports parents and teachers; monitoring, content, and releases run through agents behind human approval. QuizMonster is the live template for the AI-native operating model I help companies adopt. Launching November 2026.
Education
2001 - 2005
Bachelor's Degree in IT Engineering
Polytechnic University of Zagreb - Zagreb, Croatia
Skills
Libraries/APIs
Google Maps API, jQuery, API Development, React, Node.js, REST APIs, Mapbox API, Stripe, Stripe API, OpenAI API, React-JSS, React Flow, Google Maps, Facebook API, X (formerly Twitter) API, Amazon FPS, CanvasJS, WhatsApp API, Telegram Messenger API, Recombee API, Twilio API
Tools
Adobe Photoshop, ChatGPT, GitHub, Expo, Claude Code, Adobe Illustrator, Figma, Git, Canvas, Slack, Redux Toolkit
Languages
PHP, HTML5, Sass, CSS, JavaScript, TypeScript, HTML, SQL, CSS3, Python, Swift
Frameworks
React Native, Redux, Next.js, Express.js, Tailwind CSS, Smarty, Genkit, MUI CSS, Ionic, AppKit, StoreKit
Paradigms
UX Design, Mobile Design, UI Design, Mobile Development, Cross-platform, Role-based Access Control (RBAC)
Platforms
Firebase, Google Cloud Platform (GCP), Mobile, Mapbox, iOS, Android, Amazon Web Services (AWS), Azure, Vercel, MacOS
Industry Expertise
Web Design
Storage
JSON, MySQL, Firebase Realtime Database, PostgreSQL, NoSQL, Cloud Firestore, SQLite, Amazon S3 (AWS S3)
Other
Pixel Perfect, Graphic Design, Ajax, User Interface (UI), Icon Design, APIs, Web Development, Front-end, Front-end Development, User Experience (UX), Software Development, Full-stack, Startups, Card Payments, Payment APIs, Credit Card Processing, Design, Development, Scanning, Ticketing, Ticket Systems, Events, Event Ticketing, Minimum Viable Product (MVP), Web & Mobile Applications, Mobile App Development, Mobile UI, Mobile UX, Push Notifications, Mobile Applications, Startup Consulting, OpenAI, App UI, App UX, Full-stack Development, UI Development, Mobile/Web Project Management, API Design, Apps, App Design, Technical Leadership, App Store, Google Play Store, Leadership, Architecture, Firebase Cloud Functions, Figma to React, Web Scraping, AI Automation, Mobile Apps, AI Chatbots, Large Language Models (LLMs), API Integration, Generative Artificial Intelligence (GenAI), RESTFul APIs, Web App Deployment, Application State Management, Cross-platform App Development, AI Copilots, OpenAI SDK, Anthropic, AI Agents, Software Architecture, AI-assisted Development, AI-generated Code, Live Chat, Artificial Intelligence (AI), Maps, Big Data, Location Services, Scraping, Unique Business Ideas, Paystack, PayPal, AI Consulting, Recommendation Systems, Supabase, Multi-tenant SaaS, New Products, CMS, Analytics, User Experience Design, Video Calling, Authentication, Authorization, Dashboards, LLM Agents, Prompt Engineering, AI-generated Video, Product Strategy
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