
Gabriel Siedler
Verified Expert in Engineering
Senior Full-stack Developer
Florianópolis - State of Santa Catarina, Brazil
Toptal member since October 5, 2016
Gabriel builds products on top of LLMs, and he gets called when the AI part has to be trusted, not just demoed. He is taking a multi-tenant PWA built with Vibe coding into production, where he found a tenant data isolation bug before writing any new code. On an AI coaching app with paying subscribers, deterministic rules generate the plan, a validator blocks unsafe output, and a suite of athlete profiles catches regressions. Before AI, he spent 15 years building with C++, React, and Node.js.
Portfolio
Experience
- Algorithms - 20 years
- Full-stack - 12 years
- Node.js - 11 years
- React - 11 years
- Software Architecture - 9 years
- TypeScript - 8 years
- Agentic AI - 2 years
- AI Agents - 2 years
Preferred Environment
Visual Studio Code (VS Code), MacOS, Claude Code, Git, Bash
The most amazing...
...thing I've built was a gigapixel microscopy viewer in C++ and React, streamed tile-by-tile like Google Maps. Now, I make LLM output predictable enough to ship.
Work Experience
Full-stack Engineer
StoryScape
- Identified a cross-tenant data isolation gap (RLS that did not actually isolate schools) before writing any new feature code.
- Replaced a hardcoded single-tenant app with configuration-driven onboarding, letting a new school launch via a config file instead of new code.
- Delivered the first phase of a tenant-management admin panel beyond the original scope, within the same budgeted hours.
- Found and fixed UX issues through hands-on testing and product experience.
- Added full mobile screen support and PWA capabilities.
- Set up a GitHub Projects board so the client could track tasks and requirements with full transparency.
Full-stack Engineer
Darrell Ventures LLC
- Designed a four-layer architecture (rules, LLM-selected parameters, a validator, and a 50-profile regression suite) replacing open-ended chat as the source of AI training prescriptions.
- Flagged missing medical disclaimers and gaps in the terms of service on an app already live.
- Benchmarked several current LLM models on cost and output quality to choose the one powering the coaching engine in production.
- Led implementation of a full React Native redesign from Figma specs, shipping numerous usability fixes from hands-on product use.
Advisory CTO
INPunto
- Built the first React Native prototype from scratch, validating the software MVP for a portable molecular diagnostics platform.
- Recruited the product designer and selected the software and hardware contractors, assembling the full delivery team from the ground up.
- Oversaw two external teams, software and hardware, that shipped a portable point-of-care diagnostics device now patent-pending in Brazil.
- Advised the founders on technology strategy and vendor decisions, keeping the software and hardware tracks aligned to the product roadmap.
- Guided delivery of a LAMP-based diagnostics platform that returns results in hours instead of days, at over 50% lower cost than lab testing.
Full-stack Developer
Araceli Biosciences Inc.
- Architected a real-time, viewport-driven image rendering pipeline across C++ back-end and TypeScript client, replacing full-image transfers with on-demand region streaming for fluid zoom and pan on gigapixel microscopy plates.
- Engineered a pixel-level inspection tool ("pixel spy") with sub-pixel coordinate mapping between rendered viewport and source image space, enabling scientists to interrogate raw intensity values at any zoom level.
- Rebuilt the intensity histogram subsystem end-to-end with thread-safe cancellation, per-FOV granularity, and channel-aware aggregation — eliminating a class of race conditions that previously corrupted analytics under concurrent load.
- Led a full-stack modernization of the application's state management layer, migrating 15+ feature domains to a typed, predictable architecture and authoring the data-flow rules now enforced across the codebase.
- Delivered end-to-end multi-depth (Z-slice) acquisition and analysis, from capture-time controls and state persistence through MIP defaults, downstream visualization, and per-slice pixel inspection across every workflow.
- Drove cross-stack support for a new high-throughput plate format, parameterizing region geometry, intensity analytics, histogramming, and thumbnails across the product - opening a new customer segment for the instrument.
- Cut perceived image-load latency dramatically by introducing thumbnail and full-image caching, hybrid memory-plus-disk loading, smart-debounced back-end calls, base64 and binary TCP transport, and parallel TIFF tile reads.
- Hardened the image-processing service for production scale: tightened mutex and thread-pool behavior, added robust cancellation propagation, and resolved long-standing zombie-state and race-condition bugs affecting end users.
- Re-architected channel-aware intensity and aggregation data flow so per-channel enablement, auto-min/max, and ratio metrics propagate cleanly from acquisition through analysis, visualization, and CSV export.
- Modernized cross-process image transport with multiple output formats and quality controls (PNG, AVIF, 16-to-8-bit conversion), batch generation endpoints, and extended-path file support for enterprise deployments.
Front-end JavaScript Developer
Doowii
- Refactored and modernized a large-scale educational platform from the ground up, transforming an unstable MVP into a production-ready product with improved architecture, maintainability, and scalability.
- Implemented pixel-perfect UI/UX based on design specifications, while fixing hundreds of bugs across the application to significantly improve reliability, performance, and overall user experience.
- Developed and optimized real-time data fetching flows and LLM-powered features, enabling responsive AI-driven educational interactions and seamless live updates throughout the platform.
Front-end Specialist
Bruker
- Built an app from the ground up to manage embedded analysis runs and visualize their results, which contain biomolecular information.
- Engineered sophisticated components and application states, facilitating the dynamic visualization and manipulation of DNA chains and traces.
- Developed the application's front end as the sole developer, collaborating seamlessly with a team of four back-end developers.
- Engaged actively with the scrum master, product owner, and team members, contributing to the successful fulfillment of intricate project requirements through effective communication and collaboration.
Content Creator
Toptal, LLC
- Innovated and developed new technical challenges to enhance the effectiveness of the screening process for prospective candidates.
- Conducted thorough reviews of front-end documentation, significantly improving recruiter awareness and ensuring precise matching of developers to engagements.
- Spearheaded various internal projects at Toptal, contributing to the overall efficiency and success of the team.
Developer Screener
Toptal, LLC
- Conducted screening interviews to evaluate candidates' skills, ensuring a rigorous selection process for entry into Toptal's esteemed developer team.
- Coordinated daily interviews efficiently with developers worldwide, fostering a diverse and dynamic talent pool.
- Contributed actively to weekly meetings to enhance and refine the overall screening and hiring process.
- Designed and implemented algorithmic challenges and tasks to evaluate candidates' programming skills effectively, ensuring a comprehensive assessment aligned with Toptal's standards.
Full-stack Engineer
Eran Balter
- Developed an app based on an existing codebase using React, TypeScript, and Redux. Created the server-side part from scratch using Socket.IO and PostgreSQL.
- Transformed a regular app into a multiplayer service with real-time interaction.
- Accomplished MVP requests before the deadline, allowing me to add more features.
- Created very complex features inside an existing codebase.
Senior Full-stack Developer
AE Studio
- Worked for great clients like Samsung for more than four years.
- Contributed to at least 15 projects—most of them with the JavaScript stack.
- Architected projects and managed developers on several projects.
Full-stack Developer
Shirt App (via AE Studio)
- Joined the team to help solve bugs due to the app's enormous complexity.
- Assisted in building the ionic logic that enabled editing HTML shapes on the fly.
- Helped manage the back-end state to replicate the front-end design, building the final art and shipping it to the selling platform.
Front-end Developer
DVN (via AE Studio)
- Created the front end from scratch using React, Redux, and the styled-components library.
- Followed Zeplin files to create the new pages and adapted them to Bootstrap for a fully responsive website.
- Collaborated with a back-end developer to accomplish tasks.
Full-stack Developer
Exceleri
- Enhanced code reliability by organizing and refactoring a significant amount of back-end code.
- Created complex workflows in React Redux, which were the application's core.
- Improved the UI/UX dramatically using themes and bundles.
- Corrected plenty of bugs in the entire application.
Full-stack Developer
Digital Dojo
- Played a pivotal role in orchestrating and managing the entire project, ensuring smooth coordination and successful execution.
- Designed and implemented intricate features innovatively using React/Redux, contributing to the project's growth and functionality.
- Addressed and resolved bugs proactively, demonstrating a keen eye for detail and a commitment to delivering a polished, error-free final product.
Full-stack Developer
SimsUshare
- Initiated and developed the entire project from inception, showcasing the ability to conceptualize and execute projects from the ground up.
- Established API and Socket.IO server components, ensuring seamless communication and robust back-end functionality.
- Crafted an intuitive and responsive front end using React/Redux, enhancing the overall user experience with modern and efficient design practices.
Front-end Developer
Enjoy
- Developed standalone components using React, contributing to the modular and scalable architecture of the application.
- Implemented new features within the admin platform, enhancing its capabilities and user functionality.
- Demonstrated proficiency in troubleshooting and resolving front-end bugs, ensuring a smooth and error-free user experience.
Full-stack Web Developer
Marmon
- Contributed to developing an analytics app focused on managing store shelf items, enhancing its functionality and user interface.
- Elevated the UI/UX by introducing a new theme—ensuring full responsiveness, down to 320 pixels, and providing enhanced user feedback.
- Conducted comprehensive code refactoring, incorporating linters with distinct JavaScript versions for the back and front ends, modularizing code, transitioning to Sass, and optimizing folder structure for improved organization.
- Expanded browser compatibility by adding support for older versions, ensuring a broader reach and accessibility for users.
- Integrated the application seamlessly with a data science report service, enhancing its analytical capabilities.
- Implemented a robust authentication layer, fortifying the app's security measures and ensuring a safer user experience.
Full-stack Developer
Bloomz
- Addressed and resolved platform-wide bugs, ensuring the overall stability and reliability of the system.
- Collaborated in developing standalone React components, contributing to a more modular and maintainable codebase.
- Implemented comprehensive unit tests for the back end, enhancing code quality and facilitating a more robust and reliable system.
Full-stack Developer
Yazabi Predictive, Inc.
- Completed assigned tasks successfully, ensuring the timely execution of outgoing deliverables.
- Enhanced the project's overall reliability and performance by systematically identifying and resolving bugs.
- Prepared the project for release, ensuring it met quality standards and was ready for deployment.
Front-end Developer
Modsy
- Collaborated in developing intricate React components, contributing to the project's sophistication and functionality.
- Translated design concepts from PSD to HTML, ensuring pixel-perfect and responsive implementations.
- Enhanced overall stability and user experience by systematically addressing and resolving platform-wide bugs.
Full-stack Web Developer
Blueshift
- Developed a soccer statistics app for a local client, showcasing proficiency in creating tailored solutions.
- Coordinated and led front- and back-end colleagues effectively—ensuring seamless collaboration and project synergy.
- Engineered the core company manager using the Kohana PHP framework, demonstrating expertise in building robust and scalable web applications.
Full-stack Web Developer
Bravi
- Contributed to developing one of the world's biggest educational systems, EBS.
- Created apps for clients like Qualcomm and Tribal.
- Led the Brazilian team's technical operations for local clients.
Full-stack Web Developer | Partner
Dauphin
- Identified prospective customers and negotiated based on the project's complexity.
- Managed contacts and sales directly with customers.
- Developed several projects for local customers and small companies.
- Designed a database using schema tools and implemented it using MySQL.
Experience
Cabritos Groceries
http://cabritos.kreakodo.comI designed and built the entire stack: the schema (lists, items, members, invites, presence), the REST API, optimistic UI client hooks with setTimeout-based polling, an in-flight mutation guard to prevent race conditions, and a duplicate-prevention layer using normalized names and a partial unique index. Other highlights include invite-link sharing with role-based authorization (owner and guest), a 30-second presence heartbeat with online indicators, autocomplete suggestions, an installable PWA with service worker, rate limiting for public launch, and a polished emerald and slate design system tuned for one-handed in-store use.
Die Das
http://diedas.kreakodo.comThe app ships with 150 curated nouns, native German pronunciations generated via edge-tts (Conrad Neural voice), accuracy-tiered completion cheers, and a themed learning path with hand-crafted island worlds for each unit. State is persisted locally, so progress survives reloads and offline use. The UI supports English and Portuguese, light and dark themes, and a configurable sound volume. The project demonstrates strong attention to micro-interactions, accessibility, and a polished feel typical of native apps, while remaining a fully installable web app.
Seriesly
http://seriesly.kreakodo.comI designed and built the project end-to-end. The stack is Next.js 16 with the App Router, React 19, TypeScript, and Tailwind CSS v4. Authentication is handled by Clerk (including Google SSO), data is persisted in PostgreSQL through Drizzle ORM, and series metadata plus regional watch providers are pulled from the TMDB API, with a server-side cache that keeps results available even when upstream calls fail.
A daily Vercel Cron job signs Web Push messages with VAPID and delivers personalized release alerts to each subscriber. The codebase includes unit tests with Vitest and React Testing Library, automated patch versioning via a git hook, and a production deployment on Vercel with environment-driven configuration.
Corre AI
http://corre.aiTibia 3D
http://tibia3d.kreakodo.comA personal side project I'd wanted to build for years: reimagining Tibia, the classic MMORPG, as a top-view 3D action-RPG. I'm not a game developer by trade—my goal was to prove that a strong web and TypeScript foundation is enough to ship (in the AI era) a complete, playable game with a large world, real-time combat, an in-game economy, and a leveling system.
Built entirely by me in React Three Fiber (Three.js, TypeScript, and Vite), running on both desktop and mobile directly in the browser.
KEY WORK
• A zero-dependency asset pipeline built with Node.js that imports the real Rookgaard map tile-by-tile from the original client and renders it in 3D—temple, village, premium west, and a 6-level underground cave—scaled to around 50,000 tiles via instanced meshes for smooth mobile performance.
• Faithful pre-8.0 systems on the original formulas: XP, leveling, melee combat, trainable skills, armor/defense, loot and gold, food regeneration, fuel-burning torches.
• NPCs, minimap with fog-of-war, i18n, local save, and a standalone 2D map editor.
Education
Bachelor's Degree in Computer Science
Federal University of Pelotas - Pelotas, Rio Grande do Sul, Brazil
Skills
Libraries/APIs
React Redux, Node.js, React, REST APIs, Socket.IO, D3.js, Three.js, Backbone.js, MobX, API Development, Stripe API, Web Audio API, LocalStorage, Context API, React Testing Library, React Hook Form, Zod, Playwright, OpenAI API, Redux Persist, React Router, Winsock API, OpenCV, Highcharts, Google Calendar API
Tools
Claude Code, Claude, NPM, GitLab, GitHub, Expo, Jenkins, Adobe Fireworks, Subversion (SVN), Git, Canvas, Drizzle ORM, Cron, Vitest, Shadcn UI, Prettier, BigQuery, Figma, Redux Toolkit, Webpack
Languages
TypeScript, JavaScript, HTML, CSS, SQL, Python, Sass, CSS3, HTML5, C++, PHP, GraphQL, SCSS, ES5, C, C++17, Bash
Frameworks
React Native, Next.js, Redux, Express.js, AngularJS, Bootstrap, Ionic 3, Angular, Tailwind CSS, CodeIgniter, Kohana, Ionic, JSON Web Tokens (JWT), Jest, Electron, Fluent UI
Paradigms
Responsive, Responsive Web Design (RWD), Unit Testing, Agile Software Development, REST, UI Design, UX Design, Mobile Development, Search Engine Optimization (SEO), Event-driven Architecture, Refactoring
Platforms
Web, Windows, Linux, Visual Studio Code (VS Code), MacOS, Vercel, Oracle, Heroku, Docker, Shopify, Android, iOS, Mobile, Clerk, Google Cloud Platform (GCP), Firebase, Amazon Web Services (AWS), Netlify
Industry Expertise
Web Design
Storage
Relational Databases, MySQL, MongoDB, PostgreSQL, JSON, Database Management, Microsoft SQL Server, NoSQL, Google Cloud
Other
User Experience (UX), Styled-components, Full-stack, Full-stack Development, APIs, Web Development, Front-end, Algorithms, Minimum Viable Product (MVP), Technical Leadership, Front-end Development, Problem Solving, User Interface (UI), Dashboards, Data Visualization, RESTFul APIs, API Integration, Real-time Data, WebSockets, Medical Imaging, AI Tools, Vibe Coding, Anthropic, Software Architecture, Website Design, Website Redesign, Websites, Troubleshooting, AI-assisted Development, Figma to React, Startups, OAuth, LLM Integration, Monorepos, Artificial Intelligence (AI), Charts, Audio, Data Structures, AI Agents, Cloud, Agentic AI, Large Language Models (LLMs), Architecture, SaaS, Mobile App Development, AI Integration, Server-side Rendering (SSR), Multi-tenant Architecture, Early-stage Startups, Analytics, Product Development, Website Performance, Back-end, React Hooks, Machine Learning, Video Compression, Visx, Axios, Back-end Development, Tailwind UI, Progressive Web Applications (PWAs), Service Workers, Optimistic UI, Pooling Architecture, Database Schema Design, Responsive UI, Access Control, Mobile-first Design, i18n, SVG Animation, CSS Animations, Text-to-Speech (TTS), Scripting, Git Hooks, Accessibility, Single Sign-on (SSO), TMDB, Web Push Notifications, Server Components, Server Actions, ESLint, Mobile First, Mastra, Radix UI, Zustand, Web Scraping, Prompt Engineering, Provider Abstraction, Edtech Design, Griffel, IPC, contextBridge, Multithreading, Concurrency, Mutexes, Atomics, Thread Pools, TCP Sockets, Binary Protocols, RAII, Smart Pointers, Exception Handling, TIFF, PNG, AVIF, Base64, RLE, Tile-based Rendering, Image Caching, Flat-field Correction, Histogram Analysis, Pixel-level Inspection, Application State Management, Performance Optimization, Memory Management, Scientific Data Analysis, Microscopy, Life Science, DocuSign, Course Development, DNS, Team Building, Product Strategy, Supabase, Push Notifications, Training, Chatbots, Fitness
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