Sergio is available for hire
Hire SergioSergio Antonio Milici
Verified Expert in Engineering
Full-stack Developer
Buenos Aires, Argentina
Toptal member since May 20, 2014
Bio
Sergio is a senior software engineer adept at architecting and delivering scalable, efficient solutions for complex challenges. He has proven expertise in full-cycle product development, from initial research and design through development, deployment, scaling, and rigorous testing.
Portfolio
StubHub - Engineering
Design Systems, React, TypeScript, UI Components...
Ofinno LLC
CSS, CI/CD Pipelines, Node.js, Next.js, Full-stack, Figma, Product Management...
Veza
React, CSS, JavaScript, HTML, APIs, REST APIs, CSS-in-JS, Cypress, Jest, Docker...
Experience
- UI Components - 15 years
- React - 10 years
- Front-end Development - 10 years
- Full-stack Development - 10 years
- Angular - 10 years
- TypeScript - 8 years
- Architecture - 5 years
- Node.js - 5 years
Preferred Environment
Angular, React, Node.js, JavaScript, HTML, TypeScript, Full-stack, UI Components, Front-end Architecture, Leadership, Communication, Complex Application User Interfaces (UI), Teamwork, ECMAScript (ES6), Large-scale Projects, HTTP, React Query, Minimum Viable Product (MVP), Startups, Refactoring, React Testing Library, Figma to React, Vercel, Claude, Third-party Integration, Integration, Workflows, Claude API, Large Language Models (LLMs), Cypress, Testing, NoSQL, NPM, Yarn
The most amazing...
...project I've created is a distributed system to control all software and hardware changes on every machine in a network.
Work Experience
Senior Front-end Engineer
2024 - 2025
StubHub - Engineering
- Researched and implemented a solution for displaying thousands of transactions in a table, with features for quick filtering, grouping, and summarization.
- Analyzed, debugged, and improved UI performance, reducing page load time by 200 ms and enabling faster user interaction.
- Designed and implemented a drag-and-drop interface for matching tickets to events, reducing user on-screen time by 10 minutes.
- Developed and enhanced reusable UI components for desktop and mobile applications, significantly reducing task implementation time for the development team.
Technologies: Design Systems, React, TypeScript, UI Components, Complex Application User Interfaces (UI), Teamwork, Platform as a Service (PaaS), ECMAScript (ES6), Large-scale Projects, HTTP, Webpack, React Query, Refactoring, React Testing Library, Figma to React, Third-party Integration, Integration, Testing
React/Full-stack Developer
2023 - 2023
Ofinno LLC
- Architected and implemented the complete project architecture, including the strategic selection of the core framework and key 3rd-party libraries, as well as the definition and management of the application state.
- Led the development and implementation of a comprehensive design system from the ground up using Storybook, ensuring consistency and reusability across the application.
- Collaborated with stakeholders to analyze project requirements and effectively managed the implementation process with other team members, ensuring alignment and efficient delivery.
- Developed and rigorously tested 100% of the project's user-facing pages and core features, guaranteeing high quality and functionality.
Technologies: CSS, CI/CD Pipelines, Node.js, Next.js, Full-stack, Figma, Product Management, Tailwind CSS, Docker, PostgreSQL, Python, Design Systems, Storybook, Third-party APIs, Redux, JavaScript, Google Analytics, Hybrid Apps, Object-oriented Design (OOD), Web Performance Optimization (WPO), Server-side Rendering (SSR), Responsiveness, Complex Application User Interfaces (UI), Teamwork, ECMAScript (ES6), HTTP, Webpack, React Query, Minimum Viable Product (MVP), Startups, Refactoring, React Testing Library, Figma to React, Third-party Integration, Integration, Testing
Front-end Architect
2020 - 2022
Veza
- Architected and implemented the foundational software framework and defined critical infrastructure requirements, enabling scalable and efficient product performance.
- Rapidly developed and delivered the initial minimum viable product (MVP) within two weeks, culminating in a successful investor presentation that secured the first funding round.
- Led and mentored a 5-engineer team to significantly accelerate product development cycles, achieving a 25% increase in feature deployment velocity.
- Implemented and maintained GitHub Actions for continuous integration (CI), automating the build process for each pull request. This included setting up a complete test environment with unit, E2E, and error reporting, as well as build generation.
Technologies: React, CSS, JavaScript, HTML, APIs, REST APIs, CSS-in-JS, Cypress, Jest, Docker, TypeScript, Next.js, AWS Lambda, GitHub, Amazon Web Services (AWS), Styled-components, Web Development, Responsive Web Apps, Storybook, API Integration, Front-end Development, Ant Design, Git, Web Applications, Unit Testing, REST, Single Sign-on (SSO), Responsive Layout, SCSS, UI Components, UI Testing, SQL, JSON Web Tokens (JWT), OAuth 2, UI Libraries, Component Libraries, Front-end Architecture, Software Engineering, Web API, JavaScript 6, Leadership, Agile, Consulting, MobX, User Interface (UI), User Experience (UX), Web Design, Web, Figma, JSON, Algorithms, CI/CD Pipelines, Design, Websites, Forms, Third-party APIs, Third-party Libraries, Design Systems, Google Analytics, Hybrid Apps, Object-oriented Design (OOD), Web Performance Optimization (WPO), Responsiveness, Complex Application User Interfaces (UI), Teamwork, ECMAScript (ES6), Large-scale Projects, HTTP, React Query, Minimum Viable Product (MVP), Startups, Refactoring, React Testing Library, Figma to React, Third-party Integration, Integration, Testing
Senior Front-end Software Engineer
2020 - 2021
TalentWall
- Developed an intuitive drag-and-drop grid system for customizable dashboards, empowering users to arrange and resize charts dynamically.
- Enhanced user navigation significantly by optimizing algorithms to efficiently process over 5,000 jobs, resulting in a 40% improvement in user experience.
- Improved app responsiveness by fixing internal algorithms to handle over 5,000 jobs in the UI.
- Engineered a suite of reusable UI filters, promoting consistency and efficiency across the application.
Technologies: Sass, TypeScript, Angular, CSS, JavaScript, HTML, NgRx, NgRx/store, Redux, RxJS, Functional Reactive Programming, APIs, Mobile Apps, Test-driven Development (TDD), GitHub, Web Development, Responsive Web Apps, AG Grid, API Integration, Front-end Development, Git, Web Applications, Unit Testing, CSV, REST, Single Sign-on (SSO), Responsive Layout, SCSS, UI Components, UI Testing, SQL, JSON Web Tokens (JWT), OAuth 2, UI Libraries, Front-end Architecture, Software Engineering, Web API, JavaScript 6, Firebase Realtime Database, Leadership, Agile, Consulting, User Interface (UI), User Experience (UX), Web, Figma, JSON, Algorithms, Design, WebSockets, Forms, Third-party APIs, Third-party Libraries, Design Systems, Google Analytics, Hybrid Apps, Object-oriented Design (OOD), Web Performance Optimization (WPO), Responsiveness, Complex Application User Interfaces (UI), Teamwork, ECMAScript (ES6), HTTP, Minimum Viable Product (MVP), Refactoring, Nx, Third-party Integration
Senior Full-stack Software Engineer
2019 - 2019
Social Camping
- Set up the back end with Node.js, Express, and Firestore to manage the user's assets.
- Integrated Firebase Auth to allow users to log in with Google, Facebook, and email and password.
- Created the front-end project with Angular and Bootstrap for implementing a CRUD to allow users to manage their camping assets.
- Implemented Figma design to create reusable UI system components.
Technologies: Bootstrap, Firebase, Angular, Express.js, Node.js, CSS, JavaScript, HTML, TypeScript, Redux, Full-stack, APIs, Full-stack Development, Ionic, GitHub, Progressive Web Applications (PWAs), Web Development, Responsive Web Apps, Storybook, API Integration, Front-end Development, Next.js, Tailwind CSS, Git, Web Applications, Unit Testing, CSV, Electron, REST, Single Sign-on (SSO), Responsive Layout, SCSS, Material UI, UI Components, GraphQL, UI Testing, SQL, JSON Web Tokens (JWT), Auth0, OAuth 2, UI Libraries, Front-end Architecture, PWA, Software Engineering, Web API, JavaScript 6, Firebase Realtime Database, Agile, User Experience (UX), Web, Figma, JSON, Design, Websites, WebSockets, Forms, Canvas, Third-party APIs, Third-party Libraries, Design Systems, Google Analytics, Hybrid Apps, Object-oriented Design (OOD), Mobile Applications, Mapbox API, Responsiveness, Complex Application User Interfaces (UI), Teamwork, ECMAScript (ES6), HTTP, MongoDB, Minimum Viable Product (MVP), Startups, Refactoring, React Testing Library, Figma to React, Third-party Integration
Front-end Engineer
2016 - 2018
Qwil
- Architected and delivered the v1.0 of Qwil's web application leveraging AngularJS.
- Drove the technical strategy and execution for migrating the entire web application to the React ecosystem, ensuring a seamless transition and future-proofing the platform.
- Pioneered the development of reusable UI components in partnership with the lead product designer, establishing Qwil's design system for consistent and efficient UI development.
- Designed and deployed a standardized E2E testing infrastructure with Docker and Nightwatch, enabling automated testing across various environments to guarantee release quality.
- Instituted and enforced unit testing best practices across the engineering team, leading to a demonstrable 50% decrease in reported software bugs and improving overall code quality.
Technologies: AngularJS, JavaScript, Django, Python, User Experience (UX), React, Redux, Large-scale Projects, HTTP, Startups, Refactoring, React Testing Library, Figma to React
Mobile Engineer
2015 - 2015
Hollaback!
- Created a hybrid HTML5 mobile app from scratch for Android and iOS using Ionic.
- Designed and implemented business logic in JavaScript following design patterns and best practices.
- Deployed builds to production for Android and iOS using TestFlight and Google Play.
- Integrated native plugins like geolocation, contacts, and keyboard.
- Integrated Facebook native login and Google Maps API.
Technologies: JavaScript, Sass, Ionic, AngularJS, CSS, HTML, Angular, Redux, Full-stack, APIs, Mobile, Cross-platform, Full-stack Development, Mobile Apps, Minimum Viable Product (MVP), GitHub, API Integration, Front-end Development, Git, Web Applications, Unit Testing, REST, Single Sign-on (SSO), Responsive Layout, SCSS, UI Components, UI Testing, JSON Web Tokens (JWT), Auth0, OAuth 2, UI Libraries, Software Engineering, Web API, JavaScript 6, Firebase Realtime Database, Web, JSON, Websites, Forms, Third-party APIs, Third-party Libraries, Google Maps, Design Systems, Object-oriented Design (OOD), Mobile Applications, App Store, Web Performance Optimization (WPO), Responsiveness, ECMAScript (ES6), HTTP, Startups
Front-end Software Engineer
2015 - 2015
Kimono (via Topta)
- Redesigned chat workflow for sending and receiving messages.
- Created the mobile version of the app using the Ionic Framework.
- Refactored and designed the OOP model to be maintainable.
- Implemented Algolia search API to show custom and fast results.
- Improved performance of startup of the mobile version and UX.
Technologies: JavaScript, CSS3, HTML5, iOS, Android, Cordova, Ionic, AngularJS, Node.js, HTML, TypeScript, Angular, CSS, APIs, Minimum Viable Product (MVP), GitHub, Web Development, API Integration, Front-end Development, Git, Web Applications, Unit Testing, Single Sign-on (SSO), Responsive Layout, UI Components, SQL, Software Engineering, Web API, Web, JSON, Forms, Third-party APIs, Google Maps, Design Systems, Hybrid Apps, Object-oriented Design (OOD), Mobile Applications, Responsiveness, Teamwork, ECMAScript (ES6), HTTP, Startups
Java DevOps Consultant
2014 - 2014
L2
- Converted five existing Java projects to Maven projects.
- Designed and implemented a configuration module to support multiple environments using Typesafe Config.
- Set up automatic builds on Jenkins and integrate it with GitHub.
Technologies: Jenkins, Apache Maven, Java, HTML, JavaScript, CSS, APIs, GitHub, Web Development, API Integration, Front-end Development, Git, Web Applications, Unit Testing, REST, SQL, OAuth 2, Software Engineering, JavaScript 6, Web, JSON, Forms, Third-party APIs, Third-party Libraries, Design Systems, Hybrid Apps, Object-oriented Design (OOD), Teamwork, Startups, Third-party Integration
Software Engineer
2012 - 2014
50Cubes
- Created back-end server for an ad-targeting system for Facebook games.
- Developed a JavaScript library to serve ads based on game states.
- Designed a real-time metric system on HTML5 for showing user conversions.
- Created a Java back-end server for a Space Pirates game. Integrated it with Android and Facebook.
- Managed AWS to support all systems, including handling databases, fail-over, and performance.
Technologies: Redis, MySQL, JavaScript, Spring, Jasmine, PHPUnit, JUnit, PHP, Python, Java, Node.js, HTML, Angular, React, Redux, Architecture, CSS, Full-stack, APIs, Full-stack Development, Mobile Apps, GitHub, Amazon Web Services (AWS), Web Development, API Integration, Front-end Development, Git, Web Applications, Unit Testing, REST, Single Sign-on (SSO), SQL, JSON Web Tokens (JWT), OAuth 2, Software Engineering, Web API, JavaScript 6, Web, JSON, WebSockets, Forms, Third-party APIs, Third-party Libraries, Design Systems, Hybrid Apps, Object-oriented Design (OOD), Web Performance Optimization (WPO), Responsiveness, Teamwork, ECMAScript (ES6), HTTP, MongoDB, Startups
Software Engineering Tech Lead
2009 - 2012
InvGate
- Created a multi-platform client-server application to control hardware and software changes over the whole network.
- Developed a multi-platform client application in C++.
- Implemented high concurrency to handle all changes on thousands of computers.
- Managed the team and development to deliver new features.
- Made the back-end to scale and processed vast amounts of data.
Technologies: Java, PHPUnit, Jenkins, Memcached, MySQL, HTML5, PHP, C++, HTML, CSS, Full-stack, APIs, Cross-platform, Full-stack Development, Minimum Viable Product (MVP), Test-driven Development (TDD), GitHub, Web Development, API Integration, Front-end Development, Git, Web Applications, Unit Testing, REST, SCSS, SQL, JSON Web Tokens (JWT), OAuth 2, Software Engineering, Web API, JavaScript 6, Web, JSON, Forms, Third-party Libraries, Design Systems, JavaScript, Hybrid Apps, Object-oriented Design (OOD), Responsiveness, Startups
C++ Developer
2006 - 2009
JDB
- Designed a stock system to control all company assets.
- Designed and implemented an MFC UI application from scratch.
- Analyzed and designed MySQL schema for handling store and sales.
- Created an installer and deployment tool for control updates.
- Designed and implemented the migration of the store system to a web platform.
Technologies: Web, Microsoft Foundation Classes (MFC), Microsoft Foundation Class (MFC) Library, MySQL, C++, HTML, CSS, Full-stack, APIs, Full-stack Development, Test-driven Development (TDD), GitHub, Web Development, API Integration, Git, Web Applications, Unit Testing, REST, SQL, Software Engineering, Web API, Third-party APIs, Third-party Libraries, Object-oriented Design (OOD), Startups
Experience
InvGate Assets
http://www.invgate.com/es/assets/Oversaw the end-to-end delivery of "Assets," an intelligent IT solution suite comprising critical metering, inventory, and change management modules. This encompassed the complete design, software engineering, and deployment, resulting in a platform enabling proactive change management and significant resource optimization for informed IT strategies.
Space Pirates
Architected and developed the robust back-end server for "Space Pirates," a mobile game on Android and iOS (Unity3D), engineered to efficiently handle thousands of concurrent users leveraging Netty and Spring frameworks
BEE Ad Server
Engineered BEE, a custom-built advertising server tailored specifically for 50Cubes' game portfolio. This solution enabled flexible and granular ad optimization for up to 100,000 concurrent users, with advanced filtering capabilities based on country, age, user settings, and specific game information.
Hollaback!
Developed and deployed the entire Hollaback mobile application (iOS and Android) using Ionic and Cordova. This included implementing all features for users to report and view instances of street sexual harassment, empowering communities to identify and avoid unsafe areas.
Restaurant Credits
Developed "Restaurant Credits," a custom web application designed to streamline the management of external vendor credits and visitor tracking for a restaurant. Key features include a dynamic dashboard providing monthly performance reports and a comprehensive history of visitor counts and credit utilization.
Funler
Here are a few options to enhance that description of your leadership on the learning platform, focusing on even stronger action verbs, highlighting the impact, and your specific contributions:
Option 1 (emphasis on strategic leadership and technical vision):
Spearheaded a team of five engineers through the complete lifecycle of a high-concurrency learning platform, providing strategic direction and mentorship across UI/UX design, component development, responsive implementation, and a scalable back-end architecture on AWS. This included architecting a database solution optimized to support thousands of concurrent users.
Option 1 (emphasis on strategic leadership and technical vision):
Spearheaded a team of five engineers through the complete lifecycle of a high-concurrency learning platform, providing strategic direction and mentorship across UI/UX design, component development, responsive implementation, and a scalable back-end architecture on AWS. This included architecting a database solution optimized to support thousands of concurrent users.
Education
2005 - 2012
Master of Engineering Degree in Information Systems Engineering
National Technological University - Buenos Aires, Argentina
Skills
Libraries/APIs
React, RxJS, NgRx, Google Maps, Node.js, Facebook API, REST APIs, Web API, MobX, Mapbox API, React Query, React Testing Library, Microsoft Foundation Class (MFC) Library, Socket.IO, X (formerly Twitter) API, YouTube API, jQuery, NgRx/store, Firebase Web SDK, AG Grid, Backbone.js, Microsoft Foundation Classes (MFC), Claude API
Tools
Capacitor, Apache Maven, Webpack 4, SAP Hybris, GitHub, Webpack, Babel, Grunt, Karma, NPM, Google Analytics, Git, Flow, Auth0, GitLab, Canvas, Apple Push Notifications, Claude, Jenkins, Amazon CloudFront CDN, Subversion (SVN), Figma, Microsoft Teams, Nx
Languages
HTML, CSS3, TypeScript, ES7, Sass, ECMAScript (ES6), HTML5, JavaScript, SQL, GraphQL, CSS, SCSS, JavaScript 6, PHP, Xtend, Java, C++, Less, Python, C
Frameworks
Next.js, Angular, Redux, Jasmine, Ionic, AngularJS, Cypress, Tailwind CSS, Ant Design, JSON Web Tokens (JWT), Yarn, Selenium, Bootstrap, Express.js, Jest, Electron, Material UI, OAuth 2, PHPUnit, JUnit, Spring, Django
Paradigms
Test-driven Development (TDD), Object-oriented Design (OOD), Cross-platform, Unit Testing, REST, Refactoring, Testing, Functional Reactive Programming, Model View ViewModel (MVVM), Model View Controller (MVC), Web Performance Optimization (WPO), Responsive Layout, Agile, Reactive Programming
Platforms
Web, Mobile, MacOS, Firebase, Windows, Linux, Amazon Web Services (AWS), Android, iOS, Docker, AWS Lambda, Vercel
Storage
NoSQL, Firebase Realtime Database, JSON, MongoDB, Redis, MySQL, Memcached, Microsoft SQL Server, Amazon DynamoDB, PostgreSQL
Industry Expertise
Web Design
Other
Freelancing, Single-page Applications (SPAs), Cordova, Hybrid Apps, Front-end Development, Progressive Web Applications (PWAs), Front-end, Full-stack, APIs, Mobile Apps, Minimum Viable Product (MVP), Styled-components, Web Development, API Integration, Web Applications, CSV, Single Sign-on (SSO), UI Components, UI Testing, UI Libraries, Component Libraries, Front-end Architecture, Software Engineering, Websites, Forms, Third-party APIs, Third-party Libraries, Design Systems, Mobile Applications, Responsiveness, Communication, Complex Application User Interfaces (UI), Teamwork, Large-scale Projects, HTTP, Startups, Figma to React, Third-party Integration, Integration, SaaS, System Administration, Open Source, Architecture, Apps, Web Components, Enzyme, Full-stack Development, Responsive Web Apps, Storybook, MERN Stack, Chrome Extensions, Vite, PWA, Leadership, Consulting, Slack App, Algorithms, CI/CD Pipelines, WebSockets, App Store, Google Play Console, Server-side Rendering (SSR), Platform as a Service (PaaS), Large Language Models (LLMs), Financial APIs, CSS-in-JS, Firebase Hosting, Web UX, User Interface (UI), User Experience (UX), Design, Product Management, Facebook Games, Ionic Appflow, Workflows
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