Juan Pablo Carzolio, PHP Developer in Benavidez, Buenos Aires Province, Argentina
Juan Pablo Carzolio

PHP Developer in Benavidez, Buenos Aires Province, Argentina

Member since November 8, 2015
Juan is a versatile and dependable full-stack engineer with twelve years of professional experience and a computer science degree. With a strong math and computer science background, he loves to apply reasoning and creativity to understand and solve challenging problems, regardless of the technologies used. He is proficient in several languages, including JavaScript and PHP, and communicates extremely well.
Juan is now available for hire


  • Grid AI
    JavaScript, HTML5, CSS3, Styled-components, GraphQL, WebSockets, React, Figma
  • MobiStream Solutions
    HTML, Cordova, Git, CSS3, JavaScript, CSS, Cypress.io, Blueprint...
  • TeselaGen
    HTML, Git, CSS3, JavaScript, CSS, Cypress.io, PostgreSQL, Enzyme, Jest...



Benavidez, Buenos Aires Province, Argentina



Preferred Environment

Git, MySQL, Tmux, Vim Text Editor, Eclipse, VS Code, MacOS

The most amazing...

...software I've written is an old-school, "2.5D" raycasting game engine, similar to Doom and Duke3D, written 100% in Java using low-level pixel calculations.


  • Lead Front-end Engineer

    2020 - 2021
    Grid AI
    • Created the front end from scratch using React, as one of the first few hires of the company.
    • Interviewed candidates in order to build the front-end team, which I then led, ticketing and assigning work to other members, and providing guidance and help to them as needed.
    • Worked in a very dynamic and fast-paced startup environment, collaborating with the back end, design, and product, as well as with my own team.
    Technologies: JavaScript, HTML5, CSS3, Styled-components, GraphQL, WebSockets, React, Figma
  • Lead Front-end Developer

    2018 - 2020
    MobiStream Solutions
    • Took over the development of an existing AngularJS application and greatly extended it, developing most of the "micro-apps" it currently consists of.
    • Introduced some React parts, aiming to eventually migrate the whole app to it. Also made some contributions and suggestions for the app's back end written in Java (Spring Boot).
    • Developed a React application for a cybersecurity company, including several CRUD sections as well as a dashboard with animated data visualizations I wrote from scratch using D3.js.
    • Created an advanced tool builder application, which allows easily creating web front ends by dragging and dropping components onto a canvas and visually configuring their properties, and wiring them together and to back ends with no/low code needed.
    • Created an "object editor" component that, given an object definition/schema, dynamically renders the appropriate forms to edit the object, including nested objects and lists (supporting drag-n-drop item reordering, removal, and more.).
    • Used Apache Cordova to create hybrid mobile apps reusing the web codebase.
    • Wrote end-to-end tests using Cypress as well as unit tests with Jest and Enzyme.
    Technologies: HTML, Cordova, Git, CSS3, JavaScript, CSS, Cypress.io, Blueprint, Styled-components, Enzyme, Jest, Lodash, YARN, ESLint, Webpack, SCSS, Bootstrap, D3.js, AngularJS, ECMAScript (ES6), React
  • Senior Full-stack Developer

    2018 - 2019
    • Worked on several related SPAs using React, Redux, GraphQL, and Node.js, among other technologies.
    • Unified the UI look and feel of multiple related applications.
    • Refactored and unified similar components across applications, extracting them into a common library.
    • Wrote unit tests using Jest and Enzyme, and functional/integration tests using Cypress.
    • Wrote scripts and configuration to get Cypress tests running in a Heroku CI environment.
    • Worked on misc features, bug fixing, code reviews, and more.
    Technologies: HTML, Git, CSS3, JavaScript, CSS, Cypress.io, PostgreSQL, Enzyme, Jest, Lodash, YARN, ESLint, Webpack, Blueprint, Node.js, ECMAScript (ES6), Redux, React
  • Full-stack Web Developer

    2018 - 2018
    Meridix (via Toptal)
    • Fixed and implemented a website redesign based on a designer's mockups.
    Technologies: HTML, Git, CSS3, SQL, PHP, JavaScript, CSS, jQuery, HTML5
  • Senior Full-stack Developer

    2017 - 2018
    Priceline (via Toptal)
    • Worked in an agile team environment, having daily standup meetings, tracking tasks using Jira, etc.
    • Designed and implemented most of the API-facing and Redux logic of the SPA.
    • Designed and implemented the overall visual structure of the app as well as many of the views and components.
    • Worked together with another front-end developer, reviewing each other's code and discussing important topics together to find the best solutions.
    • Wrote unit tests and test helpers for most major functions and React components, using Jest and Enzyme.
    • Made smaller contributions and suggestions for the app back end too, written in Java (Spring Boot).
    • Designed the overall app authorization system based on permissions and roles.
    Technologies: HTML, Git, CSS3, JavaScript, CSS, Enzyme, Jest, Lodash, YARN, ESLint, Webpack, Bootstrap, ECMAScript (ES6), Redux, React
  • Full-stack Web Developer

    2017 - 2017
    Meridix (via Toptal)
    • Migrated a messy old-style PHP codebase to Laravel 5.
    • Redesigned and migrated the UI using Bootstrap, custom CSS, Less, jQuery and "vanilla" JS.
    • Implemented various charts in the dashboard using Chart.js.
    • Fixed bugs and solved migration issues.
    • Rewrote many hardcoded SQL queries using Eloquent and/or parameter binding.
    Technologies: HTML, Git, CSS3, SQL, PHP, JavaScript, CSS, Redis, Chart.js, jQuery, Less, Bootstrap 3, Laravel 5
  • Architect and Lead Developer

    2016 - 2017
    Vistrata (via Toptal)
    • Took over an existing base project, which I improved and extended.
    • Designed and Implemented a lightweight data access layer to replace a slow custom ORM layer.
    • Designed and implemented a JavaScript component to efficiently render Gantt-like bars from input row data of unlimited size.
    • Implemented Ag-Grid throughout the app to display grids, using custom code to integrate with my Gantt component, add unsupported features, etc.
    • Designed and implemented a technique to batch CRUD operations on the front end and process them asynchronously on the back end, allowing for seamless editing with autosave (Google Docs style) and enabling offline editing.
    • Designed the basics of an advanced data revision control system to be implemented in the DB, which is efficient in both space and time.
    Technologies: Amazon Web Services (AWS), HTML, Git, Amazon EC2, CSS3, SQL, PHP, JavaScript, CSS, AWS, Vagrant, JSON, REST, MySQL, Gulp, Ag-Grid
  • Developer

    2015 - 2016
    CertaPet (via Toptal)
    • Worked with the founders to design and build a platform MVP that would allow their existing business concept to scale.
    • Suggested a split architecture consisting of a PHP back end with a REST API and a SPA front end.
    • Designed the DB schema and implemented all of the back end and API, working together with a front-end developer that got hired later.
    • Integrated Stripe payments trying out different flows, including "auth and capture."
    • Integrated several other third-party services, including Mandrill, Wufoo, WebMerge, and HelloSign.
    • Designed and built the back-end infrastructure in AWS, using RDS, EC2, S3, and IAM.
    Technologies: Amazon Web Services (AWS), Git, Amazon EC2, SQL, PHP, hellosign, Jira, Trello, AWS, WebMerge, Wufoo, Mandrill, Stripe, JSON, REST, MySQL
  • Freelance Software Developer

    2011 - 2015
    6v Soft
    • Joined and led a small remote team that worked on feature development, maintenance, bug fixes, optimization, and testing of a high-traffic (2+ million daily active users) application on the Facebook platform.
    • Helped maintain, optimize, and migrate the app’s cloud infrastructure based on AWS and Rightscale, including load balancing (ELB), web server arrays, Memcached servers, Cron servers, RDS, S3, Route53, and CloudFront.
    • Developed for an advanced in-house statistics system that allowed real-time monitoring of various traffic metrics.
    • Led the development of mobile web and hybrid (Cordova) versions of the application.
    • Performed A/B testing and experiments to guide feature and design decisions.
    Technologies: Amazon Web Services (AWS), HTML, Cordova, Amazon EC2, SQL, PHP, JavaScript, CSS, PhoneGap, AWS, Apache, MySQL, Memcached, Facebook API
  • Freelance Web Developer

    2007 - 2014
    Estudio F
    • Developed small and medium websites using HTML, JavaScript, PHP, and Flash.
    • Acquired knowledge of and experience in base web technologies.
    Technologies: HTML, PHP, JavaScript, CSS, Flash ActionScript, Flash
  • App Developer/Owner

    2009 - 2011
    • Owned and developed several applications on the Facebook platform (including two games) reaching a total traffic of 70,000 daily active users at their peak.
    • Developed an ad network mixing system that maximized revenue by optimizing each network’s traffic share based on their performance (eCPM).
    • Developed a custom analytics system to track app signals (events) based on users’ countries, languages, genders and dates, allowing for A/B testing of certain features and UI choices.
    • Developed the front-end using HTML, CSS, JavaScript, and ActionScript/Flash, the back-end with PHP, Facebook API, and MySQL, and configured Apache on CentOS and Amazon Linux servers.
    • Created and edited all original and derived artwork with Photoshop.
    Technologies: HTML, Amazon EC2, CSS3, SQL, PHP, JavaScript, CSS, Apache, MySQL, Facebook API, Flash, Flash ActionScript
  • Developer

    2008 - 2009
    • Designed and implemented a system to transfer large files over HTTP from within web applications, with advanced features like pause, resumption, and recovery of uploads and downloads.
    • Designed and implemented a system to transcode media files (images and video) for client applications that featured media previews.
    • Gained deeper understanding and experience in the JavaScript language.
    • Wrote standalone documentation for systems I built.
    • Gained experience in Java web development, learning various frameworks and tools along the process.
    Technologies: HTML, JavaScript, CSS, Oracle, Apache Tomcat, Apache, Maven, Hibernate, Spring, Servlet, Applets, Java
  • Developer

    2006 - 2006
    • Designed and implemented an algorithm for classroom assignment based in heuristics.
    • Implemented a reservation service and DAO within a Hibernate/Spring architecture.
    Technologies: SQL, Apache Tomcat, Maven, Hibernate, Spring, Java


  • MegaSlots

    A themed "artisanal" slot machine game I built from scratch, implemented as an app for the Facebook platform. It features a rich front-end written both in ActionScript and JavaScript, and a PHP/MySQL back-end. It reached 5k daily users.

  • Solitarium 35

    A card solitaire game I built from scratch, implemented as an app for the Facebook platform. It features a rich front-end written mainly in ActionScript, and a PHP/MySQL back-end.

  • Blog

    My personal website and blog. You can find a portfolio section there, as well my CV.

  • A Guide to Consistent Hashing (Publication)
    Consistent Hashing is a distributed hashing scheme that operates independently of the number of servers or objects in a distributed hash table. It powers many high-traffic dynamic websites and web applications. In this tutorial, Toptal Freelance Software Engineer Juan Pablo Carzolio will walk us through what it is and how hashing, distributed hashing and consistent hashing work.


  • Languages

    CSS, ECMAScript (ES6), HTML, PHP, JavaScript, CSS3, HTML5, Java, SQL, C, Flash ActionScript, SCSS, GraphQL, Sass, Less, Pug, Visual Basic 6 (VB6), Perl, Assembly, ActionScript 2, Lisp, Google Apps Script
  • Libraries/APIs

    React, React Router, jQuery, Ag-Grid, HTML5 Canvas, Facebook API, Stripe API, Lodash, Stripe, Chart.js, Node.js, jQuery UI, Java 2D, Wufoo API, Mandrill API, D3.js
  • Other

    Freelance, Enzyme, Data Structures, Algorithms, HTTP, HTTPS, Image Processing, Ajax, Relational Database Services (RDS), Styled-components, Cordova, AWS, hellosign, ESLint, WebSockets, PHP/Java Bridge, HTML Email, WordPress Plugins, Blade, TCP/IP, Mobile Web, Computer Graphics, Multithreading, Neural Networks, Genetic Algorithms, AI Programming, Audio, Applets, Unix Shell Scripting, Cryptography
  • Frameworks

    Redux, React-Bootstrap, Jest, Eloquent, Bootstrap, Bootstrap 3, Blueprint, AngularJS, Cypress.io, Spring, Hibernate, YARN, Lumen, Laravel 5, Laravel, Swing, PhoneGap, PHPUnit
  • Tools

    Atom, Vim Text Editor, Cron, Amazon CloudFront CDN, Git, Adobe Photoshop, Apache, Eclipse IDE, Microsoft Excel, VS Code, Tmux, Flash, Servlet, Wufoo, WebMerge, Figma, Redux Thunk, Webpack, Apache Tomcat, Xdebug, Vagrant, Gulp, Composer, Subversion (SVN), Maven, Firebug, Wireshark, FlashDevelop, DataTables, LaTeX, Jira, Trello, Basecamp
  • Paradigms

    REST, Functional Programming, Object-oriented Programming (OOP), Imperative Programming, Prototype-based OOP, Agile Software Development, Concurrent Programming
  • Platforms

    CentOS 6, Linux, Amazon EC2, Amazon Web Services (AWS), Ubuntu, Visual Studio Code, MacOS, Eclipse, Mandrill, PDF.js, WordPress, Oracle
  • Storage

    MySQL, AWS S3, Memcached, JSON, Redis, NoSQL, PostgreSQL


  • Engineer's Degree in Computer Science
    2003 - 2007
    Instituto Tecnológico de Buenos Aires (ITBA) - Buenos Aires

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