Federico Pereiro, Open Source Developer in Leiden, Netherlands
Federico Pereiro

Open Source Developer in Leiden, Netherlands

Member since November 4, 2015
Federico is a full-stack JavaScript developer and open source contributor. He works remotely with international customers, specifying, implementing, and provisioning web applications. His focus is on developing radically simple systems for solving complex problems.
Federico is now available for hire




Leiden, Netherlands



Preferred Environment

Chrome, Redis, Node.js, Vim Text Editor, Linux

The most amazing...

...thing I've done is design a set of JavaScript DSLs to create the different parts of a web application.


  • Production Scheduler

    2020 - 2021
    Kirncroft Engineering Ltd
    • Developed a web-based system for production scheduling to replace an existing VBA/Excel system.
    • Designed and documented the scheduling logic to make it idempotent and consistent while maintaining utmost flexibility.
    • Designed and implemented the UI for the system, including Gantt charts.
    Technologies: Node.js, Agile Software Development, JavaScript
  • Senior Back-end Developer

    2019 - 2019
    • Added core functionality to the back end of an application.
    • Designed and implemented an integration test suite.
    Technologies: React, PostgreSQL, Sequelize, Redis, Node.js
  • Back-end Developer

    2018 - 2019
    • Created a suite of tests for existing software.
    • Developed a tool for managing EC2 instances and a UI for performing common tasks related to instance management.
    • Refactored and improved parts of the existing codebase.
    • Worked on provisioning scripts to streamline the development cycle.
    Technologies: CSS, HTML, MongoDB, Redis, Node.js
  • Senior Back-end Developer

    2017 - 2018
    • Designed and implemented a set of standalone servers to interact with physical entertainment attractions.
    • Created a set of functional web admins to manage data and configure the aforementioned servers.
    Technologies: API Design, HTML5, Redis, Node.js, APIs, Back-end
  • Lead Back-end Developer, DevOps

    2014 - 2016
    • Undertook a complete rewrite of the Node.js back end, which was completed successfully under significant time pressure.
    • Set up provisioning, monitoring, and automation for a successful worldwide launch of a new mobile game.
    • Rewrote the file system module of the application, solving most reliability and performance issues.
    • Maintained and expanded the code and infrastructure to support additional features and multiple games.
    Technologies: API Design, Docker, Elasticsearch, Redis, Node.js, MySQL
  • Programmer, DevOps

    2013 - 2013
    • Wrote development stories to help set priorities for the development team.
    • Developed large sections of the back-end logic (including a REST endpoint to support an autocomplete for geographical information).
    • Set up provisioning, monitoring, and automation for the infrastructure.
    Technologies: Amazon Web Services (AWS), AngularJS, MongoDB, Redis, Node.js
  • Programmer, DevOps

    2012 - 2013
    • Debugged and added features to Rails and Erlang applications.
    • Handled stress testing of existing applications using Node.js.
    • Deployed, automated, and monitored tasks for applications running on AWS.
    Technologies: Unix, Puppet, Redis, Node.js, Erlang, Ruby on Rails (RoR)
  • Technology Lead

    2011 - 2012
    • Handled functional analysis of the platform.
    • Organized the transition from the old version of the platform to a new one, helping find the team and organizing development.
    Technologies: Node.js, PHP
  • Financial Analyst, Developer

    2009 - 2010
    Darwin Inversiones
    • Designed tools for rapid information retrieval from diverse data sets with public company information.
    • Designed and implemented a macro for retrieving, organizing, and presenting financial information from Capital IQ.
    • Designed and implemented a macro for taking a set of internal spreadsheets and updating them with information from Capital IQ.
    Technologies: Visual Basic, Capital IQ


  • Ustack – A Web Application Stack Focused on Understanding

    Designed, developed, and maintained a stack of open-source JavaScript libraries for building web applications.

    The stack comprises front- and back-end features and is composed of ten libraries: dale (functional loops), teishi (validation), lith (HTML/CSS generation), recalc (event system), cocholate (DOM manipulation), gotoB (a front-end framework integrating the previous five libraries), cicek (a web server), giz (an authentication layer), astack (asynchronicity) and kaboot (devops toolset).

    The ustack has been forged through radically minimizing the lines of code of each of its libraries. The entire ustack actually cannot be more than 4096 lines (2048 front-end + 2048 back-end).

  • Backendlore

    A detailed technical document specifying how I write back ends for web applications. It covers server architecture, stack decisions, authentication, validation, code structure, provisioning, and maintenance.

  • OneMillionLoops

    An application for musicians of all ages and skill levels. Create bands with matching loops of multiple instruments and genres. Practice, jam, and compose with fresh music always!

    I am the CTO of the company and have implemented the front end and back end.

  • Declarative Programming: Is It A Real Thing? (Publication)
    In a nutshell, declarative programming consists of instructing a program on what needs to be done, instead of telling it how to do it. This approach involves providing a domain-specific language (DSL) for expressing what the user wants. This DSL shields users from messy low-level constructs while still achieving the desired end-state. While declarative programming offers advantages over the imperative approach it replaces, it’s not as straightforward as it may seem. In this comprehensive article, Toptal Freelance Software Engineer Federico Pereiro outlines his experience with declarative tools and explains how you can make declarative programming work for you.


  • Languages

    JavaScript, HTML5, HTML, CSS, Visual Basic, PHP, Erlang
  • Frameworks

    Vanilla JS, Chrome, AngularJS
  • Libraries/APIs

    Node.js, REST APIs, jQuery, React, Vue
  • Paradigms

    Web Architecture, Requirements Analysis, Functional Programming, Microservices, Agile Software Development
  • Storage

    Redis, Data Validation, Amazon S3 (AWS S3), Elasticsearch, PostgreSQL, MongoDB, MySQL
  • Other

    Open Source, APIs, Architecture, System Design, API Design, Software Architecture, Back-end, Full-stack, Data Architecture, CTO, Capital IQ
  • Tools

    Git, Vim Text Editor, BrowserStack, Puppet, Sequelize
  • Platforms

    Amazon EC2, Unix, Linux, Docker, Amazon Web Services (AWS)


  • B.A. Degree in Business Administration
    2003 - 2009
    Universidad Torcuato di Tella - Buenos Aires, Argentina
  • B.A. Degree in Political Science
    2003 - 2008
    Universidad Torcuato di Tella - Buenos Aires, Argentina

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