Publication
Linux Best Practices and Tips by Toptal Developers
https://www.toptal.com/developers/linux/tips-and-practices
John is available for hire
Hire JohnJohn Kapolos
Verified Expert in Engineering
Full-stack Developer
Heraklion, Greece
Toptal member since September 9, 2015
Bio
John has been freelancing since the early 2000s, full-time remotely for US and UK companies as a senior software engineer. He specializes in React/TS and Node.js/Rust. John is an AI native—a super early AI adopter. In his spare time, he maintains his personal distributed infrastructure for fun.
Portfolio
Evinced
React, TypeScript, Cypress, React Testing Library, Webpack, Supabase...
Velo
TypeScript, Webpack 5, WebSockets, Design Systems, Software Architecture...
Toptal Project - Advanced Crypto Wallet
JavaScript, React, Web3.js, Ethers.js, Crypto, APIs, Blockchain, HTML, CSS...
Experience
- PHP - 16 years
- JavaScript - 16 years
- Node.js - 8 years
- React - 7 years
- TypeScript - 6 years
- Functional Programming - 5 years
- Serverless - 5 years
- Ember.js - 5 years
Work Experience
Senior Software Engineer
2025 - 2026
Evinced
- Implemented the new accessibility report dashboard, used by clients such as Amazon, Verizon, etc.
- Created a new component for the internal accessibility-first UI framework.
- Fixed bugs and added features in other client-facing web tools.
Technologies: React, TypeScript, Cypress, React Testing Library, Webpack, Supabase, Design Systems, Software Architecture, Artificial Intelligence (AI), Claude, AI Prompts, Agentic AI, ChatGPT, Harness, AI Workflow, ChatGPT Prompts
Senior Front-end Developer
2025 - 2025
Velo
- Re-wrote the whole front-end codebase from scratch in a modern and sustainable way, using best practices.
- Implemented performance optimizations in displaying large volumes of financial data.
- Removed tons of technical debt and enhanced features.
Technologies: TypeScript, Webpack 5, WebSockets, Design Systems, Software Architecture, Artificial Intelligence (AI), Claude, AI Prompts, Agentic AI, ChatGPT, Harness, AI Workflow, ChatGPT Prompts
Senior Full-stack Developer
2022 - 2022
Toptal Project - Advanced Crypto Wallet
- Created integrations with multiple blockchains, like Bitcoin, LTC, DOGE, Ethereum, Polygon, Solana, etc.
- Implemented full crypto token support (ERC-20, BEP-20, ERC-721).
- Implemented exchange and currency integrations.
Technologies: JavaScript, React, Web3.js, Ethers.js, Crypto, APIs, Blockchain, HTML, CSS, Front-end, HTML5, TypeScript, REST APIs, GraphQL, Apollo, Jest, Responsive UI, Full-stack, Electron, Amazon Web Services (AWS), Cryptocurrency Wallets, Full-stack Development, Third-party APIs, Responsive Design, UI Components, API/Services Architecture, API Design, ESLint, CI/CD Pipelines, API Integration, Test Automation, Web3, UI Libraries, GitHub, Figma, Single-page Applications (SPAs), Front-end Development, Ethereum, Solana, Startups, Cryptocurrency, Architecture, WebSockets, Cypress, React Testing Library, Webpack, Design Systems, Google Cloud, Software Architecture
Senior Full-stack Developer
2018 - 2022
Legacy Research Group
- Architected and developed the whole front-end React app from scratch to completely replace the previous technology (WordPress) for all the client's brands (highly modular and customizable for each brand).
- Created APIs (Node.js, AWS Serverless) to help with the back-end development.
- Built, maintained, and expanded the web app that powers a $200 million/year product fulfillment process across multiple brands.
Technologies: React, Serverless, Node.js, TypeScript, PureScript, Redux, HTML, CSS, JavaScript, Front-end, HTML5, Blockchain, REST APIs, GraphQL, Apollo, Jest, Responsive UI, Full-stack, PostgreSQL, Amazon Web Services (AWS), Payment APIs, Admin Panels, Analytics, Full-stack Development, Third-party APIs, Responsive Design, MongoDB, Next.js, UI Components, Amazon Cognito, Tailwind CSS, Express.js, Microservices, Redis, API/Services Architecture, API Design, ESLint, Kubernetes, CI/CD Pipelines, Sentry, API Integration, AWS Lambda, Test Automation, Single Sign-on (SSO), Web3, UI Libraries, GitHub, Hasura, Figma, Single-page Applications (SPAs), Python, Prompt Engineering, Large Language Models (LLMs), Front-end Development, UI Design, Rust, DevOps, APIs, Amazon DynamoDB, Material UI, Architecture, OpenAI API, Cryptocurrency, Stripe, WebSockets, Cypress, React Testing Library, Webpack, Vercel, Design Systems, Software Architecture
Back-end Node.js Developer
2018 - 2018
SPARK!
- Created a system to render arbitrary HTML into PDF.
- Implemented rendering to PDF via HTML templates/partials and integrated everything with their data back end.
- Exported reports to Google Sheets via templates, integrating the reports with the team drive and back end.
Technologies: Rendering, PDF, Browser Automation, Linux, Google APIs, Node.js, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, Jest, Back-end, PostgreSQL, Amazon Web Services (AWS), Payment APIs, Full-stack Development, Third-party APIs, Express.js, Microservices, Redis, API/Services Architecture, API Design, ESLint, Kubernetes, API Integration, UI Libraries, GitHub, Hasura, Single-page Applications (SPAs), Startups, APIs, Design Systems, Software Architecture
Front-end Developer
2018 - 2018
Terrashow
- Implemented streaming USB camera to browser (local).
- Implemented peer to peer video streaming via WebRTC (remote).
- Implemented channels—users can stream their own camera and also view other channels.
- Created the members' site.
Technologies: WebRTC, React, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, TypeScript, Responsive UI, Full-stack Development, Third-party APIs, Responsive Design, ESLint, API Integration, UI Libraries, GitHub, Hasura, Single-page Applications (SPAs), Front-end Development, UI Design, Startups, Software Architecture
Full-stack Node.js and React Developer
2017 - 2017
SBProject, LLC (via Toptal)
- Implemented a customized S3 file sharing on Lamda using serverless.
- Implemented the MVP for a calling-center SPA, using React (+MobX).
- Implemented the MVP for lead-reporting.
- Implemented deeply integrated authentication with AWS Cognito.
Technologies: Serverless, React, Node.js, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, GraphQL, Apollo, TypeScript, Jest, Back-end, Full-stack, PostgreSQL, Amazon Web Services (AWS), Payment APIs, Admin Panels, Full-stack Development, Third-party APIs, Responsive Design, UI Components, Microservices, API/Services Architecture, API Design, ESLint, Kubernetes, CI/CD Pipelines, API Integration, UI Libraries, GitHub, Hasura, Single-page Applications (SPAs), Front-end Development, Startups, APIs, Architecture, Software Architecture
Freelance Front-end Developer
2017 - 2017
QPID Health (via Toptal)
- Refactored the client's old Ember API to the newest and latest.
- Implemented a series of new features on the front-end as the corresponding endpoints from the back-end became available.
Technologies: Ember.js, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, Jest, Responsive UI, Admin Panels, Full-stack Development, Third-party APIs, Responsive Design, UI Components, API/Services Architecture, API Design, ESLint, Kubernetes, CI/CD Pipelines, API Integration, UI Libraries, GitHub, Hasura, Single-page Applications (SPAs), Front-end Development, Startups, Material UI, Software Architecture
Front-end Developer
2017 - 2017
Joinesty (via Toptal)
- Reviewed the existing extension and created a plan for the Safari implementation without rewriting/forking the app.
- Identified the Chrome extension API that had to be stubbed for Safari.
- Create a compatibility layer between Chrome/Safari for the previously identified API subset to be used as a drop-in addition for the extension to run on Safari.
Technologies: Safari, Chrome Extensions, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, Jest, Responsive UI, Full-stack Development, Third-party APIs, Responsive Design, UI Components, ESLint, API Integration, UI Libraries, GitHub, Single-page Applications (SPAs), Front-end Development, UI Design, Startups, Software Architecture
Freelance Front-end Developer
2016 - 2017
Funding Gates (via Toptal)
- Migrated an old hybrid Ember 1/Rails app to Ember 2 with proper API support.
- Implemented new features that helped brings the company offer to the mid-size market, netting hundreds of thousands in new sales in the first few months.
- Completely rewrote the test suite using the latest best practices.
- Worked locally in the company's Manhattan office for ~40 days along with the rest of the team during the re-launch period.
Technologies: Ember.js, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, GraphQL, Apollo, Jest, Responsive UI, PostgreSQL, Admin Panels, Full-stack Development, Third-party APIs, Responsive Design, UI Components, API/Services Architecture, API Design, ESLint, CI/CD Pipelines, API Integration, UI Libraries, GitHub, Hasura, Single-page Applications (SPAs), Front-end Development, UI Design, DevOps, Startups
Freelance Web Developer
2016 - 2017
Techstars.com (via Toptal)
- Tasked to make changes to the company's main site in order to add new functionality and a new design to part of it.
- Converted from designer files to a WordPress theme.
- Implemented user features in the WordPress back-end.
- Implemented WordPress widgets.
- Created responsive design with extra mobile optimizations as per the designer's schemata.
- Retained for fixed/enhances after the bulk of the work completed.
Technologies: CSS, JavaScript, PHP, WordPress, HTML, Front-end, HTML5, REST APIs, Back-end, Responsive UI, Full-stack, Full-stack Development, Third-party APIs, Responsive Design, API/Services Architecture, API Design, ESLint, API Integration, UI Libraries, GitHub, Front-end Development, UI Design, DevOps, APIs
Freelance Ember.js Developer
2016 - 2016
100yea.rs (via Toptal)
- Handled the bulk of Ember development on a large project for one of the company's clients, totaling around forty non-trivial components, 250 "pages," and over 700 tests.
- Contributed to key architectural decisions early in the project, responsible for taking it in the way in was implemented.
Technologies: Ember.js, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, Responsive UI, Full-stack, Analytics, Full-stack Development, Third-party APIs, Responsive Design, UI Components, API/Services Architecture, API Design, ESLint, API Integration, UI Libraries, GitHub, Single-page Applications (SPAs), Front-end Development, UI Design
Freelance Full-stack Developer
2016 - 2016
Future Drone Cloud (via Toptal)
- Created the back-end as an OwnCloud app via its respective framework (code + DB).
- Created a JSON API service for the OwnCloud back-end to expose the functionality to the front-end.
- Created the front-end SPA for the job submissions and general client functionality (in Ember.js).
- Created the front-end SPA for the administrators/management and related functionality (in Ember.js).
- Created the system for contract generation from the job submission data and manual entries.
- Created the integrations with third-party systems such as RightSignature (document signing) and Google Maps.
Technologies: MySQL, PHP, OwnCloud, JSON API, Ember.js, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, Back-end, Responsive UI, Full-stack, PostgreSQL, Admin Panels, Analytics, Full-stack Development, Third-party APIs, Responsive Design, API Design, ESLint, API Integration, UI Libraries, GitHub, Single-page Applications (SPAs), Front-end Development, UI Design, DevOps, Startups, APIs, Architecture
Freelance Front-end Developer
2015 - 2015
100yea.rs (via Toptal)
- Developed for the TED Ed analytics back-end as a drop-in extra programmer under TED's Sam Selikoff.
- Fixed open issues (bugs and improvements).
- Created the front-end of the demographics section of the analytics platform.
- Created all the Ember components for the Demographics section.
- Refactored previous code to make it generic enough for reuse over different sections of the platform.
- Conducted unit tests and integration tests.
Technologies: Git, CSS, Emacs, JavaScript, Ember.js, HTML, HTML5, REST APIs, Responsive UI, Full-stack, Analytics, Full-stack Development, Third-party APIs, Responsive Design, API Design, ESLint, API Integration, UI Libraries, GitHub, Front-end Development, UI Design, APIs
Full-stack Web Developer
2014 - 2015
CarlsDesk
- Architected the design of the system in all its details for efficiency and scalability.
- Created the APIs (customer-facing, back-end-facing, and internal).
- Created the customer-facing front-end.
- Created the administrator back-end as an SPA (Single Page App) with Ember.js.
- Created the mobile native application in Appcelerator.
Technologies: Appcelerator, MySQL, ArangoDB, Ember.js, Node.js, PHP, HTML, CSS, JavaScript, Front-end, HTML5, REST APIs, Back-end, Responsive UI, Full-stack, PostgreSQL, Admin Panels, Analytics, Full-stack Development, Third-party APIs, API Integration, UI Libraries, Front-end Development, UI Design, DevOps, Startups, APIs, Architecture
Full-stack Developer
2014 - 2015
Crowdster (ex-Karma411)
- Developed fully customized WordPress features.
- Created front-end responsive designs.
- Did AWS DevOps.
- Integrated with legacy systems.
- Created speed/SEO optimizations on the existing platforms.
Technologies: Front-end, Node.js, PHP, WordPress, HTML, CSS, JavaScript, HTML5, REST APIs, Back-end, Full-stack, Admin Panels, Full-stack Development, Front-end Development, DevOps, APIs
Full-stack Developer
2012 - 2013
EventNow
- Merged their three different back ends into one system.
- Implemented the design and features of "version 2" of the site.
- Performed DevOps on multiple platforms and their respective systems.
- Created automation systems for backups/emails, etc.
- Created data-based insights via statistical analysis.
Technologies: Front-end, MySQL, PHP, HTML, CSS, JavaScript, HTML5, REST APIs, Back-end, Full-stack, Analytics, Full-stack Development, Front-end Development, DevOps, APIs, Architecture
Loan Officer
2008 - 2011
Cooperative Bank of Chania
- Started as a teller, worked my way up to main teller and customer service and ultimately into loans.
- Attended various off-time seminars in the sector.
Technologies: Finance
Developer
2002 - 2011
Freelance
- Created a desktop application that monitors users' installed applications and automatically upgrades them to the latest version on the background. Also created the required administration back-end in PHP.
- Built an SEO checking tool that examines around 30 factors of a site and then gave it a rank along with explanations of what is great and what is lacking.
- Developed an eCommerce website for a local company in Magento, syncing catalog data from their legacy database system.
- Programmed a phone application for two-factor authentication.
- Developed a system that processed gigabytes of structured data and allowed the user to query via a web page for drilled down information in near real-time (max ten seconds' response time).
- Built various aggregation/integration systems based on third-party APIs (Amazon, Facebook, Twitter, etc).
Technologies: Front-end, Appcelerator, .NET, ArangoDB, Ember.js, Node.js, PHP, HTML, CSS, JavaScript, HTML5, REST APIs, Back-end, Auth0, Payment APIs, Admin Panels, Full-stack Development, Front-end Development
Mathematics Instructor
2007 - 2008
Private and Public Schools
- Taught basic algebra to middle school kids.
- Taught calculus, geometry, and statistics to high school kids.
- Taught advanced statistics, linear optimization, and graph theory to university students.
Technologies: Optimization, Geometry, Algebra, Calculus, Graph Theory, Statistics
Project History
Pramda: Practical Functional Programming in PHP
https://github.com/kapolos/pramdaA library to make functional programming in PHP practical, effective, and easy to use. Features automatically curried functions and baked-in lazy evaluation with a ton of functions for easy and practical use. Fully tested, with a lot of documentation (and much more docs coming up soon).
React-Godfather
https://github.com/kapolos/react-godfatherReact-Godfather aims to explore an alternative mental model for function components. It adds a thin layer between your shiny components and React, quietly instrumenting things behind the scenes - and it wants to make you an offer you can't refuse.
Here is what you get:
• A very natural, top-down local state management which does not feel like a DSL.
• Plays great with your existing code - you can progressively adopt it in your code-bases.
• Fully Asynchronous components to await all you want, even within the render function.
• Supports Async generators, for all your yielding extravaganzas.
Code-splitting without wrapping.
• Wings for your junior team colleagues.
Here is what you get:
• A very natural, top-down local state management which does not feel like a DSL.
• Plays great with your existing code - you can progressively adopt it in your code-bases.
• Fully Asynchronous components to await all you want, even within the render function.
• Supports Async generators, for all your yielding extravaganzas.
Code-splitting without wrapping.
• Wings for your junior team colleagues.
Crete | Ergonomic, Thread-safe and Flexible State Management
Crete is a procedural macro that simplifies state management in Rust in a flexible way.
It generates code for atomic access to a struct's fields using an RwLock and a static store, making it easier to work with shared state in both synchronous and asynchronous contexts. Because users can implement practically anything on the struct, Crete allows for a flexible store that can be tailored to a variety of needs. Perhaps you'd like to use it to build a Redux-style store. Maybe you enjoy having a billion custom setters. Perhaps you just enjoy mutating everything directly. Or maybe you even have your own homemade style of setters and getters that you love best?
No restrictions.
It generates code for atomic access to a struct's fields using an RwLock and a static store, making it easier to work with shared state in both synchronous and asynchronous contexts. Because users can implement practically anything on the struct, Crete allows for a flexible store that can be tailored to a variety of needs. Perhaps you'd like to use it to build a Redux-style store. Maybe you enjoy having a billion custom setters. Perhaps you just enjoy mutating everything directly. Or maybe you even have your own homemade style of setters and getters that you love best?
No restrictions.
Pancha AI
https://preview.pancha.aiA cross-platform coding assistant app (full GUI, not an IDE fork). Think Aider with a GUI.
Stack used: Rust/React/Tauri.
Privacy first: heavily optimized for configuration and built to be IDE agnostic before it was cool.
Stack used: Rust/React/Tauri.
Privacy first: heavily optimized for configuration and built to be IDE agnostic before it was cool.
Education
2018 - 2022
Master's Degree in Software Engineering
Harvard Extension School - Cambridge, MA, USA
2005 - 2007
Master of Science Degree in Economic Theory and Policy
University of Crete - Crete
2000 - 2004
University Degree in Applied Mathematics
University of Crete - Crete
Skills
Libraries/APIs
React, Ember Data, jQuery, Node.js, REST APIs, OpenAI API, React Testing Library, MobX, Stripe, JSON API, WebRTC, Google APIs, Google API, Amazon EC2 API, X (formerly Twitter) API, Facebook API, Amazon API, Web3.js, React Redux, TensorFlow
Tools
PHP-FPM, Apache, NGINX, Stylus, Figma, Claude, Webpack, AI Prompts, ChatGPT, Varnish, GitHub, Git, PhpStorm, Brunch, Gulp, Grunt, Sequelize, Vagrant, Auth0, Amazon Cognito, Sentry, WebStorm, Appcelerator, Emacs, SaltStack, Ansible, MATLAB, Adobe Photoshop, Appcelerator Titanium, Webpack 5
Languages
CSS, PHP, HTML5, JavaScript, ECMAScript (ES6), TypeScript, HTML, GraphQL, Rust, SQL, Less, Haml, Visual Basic .NET (VB.NET), ES7, Sass, Python, Bash Script, PureScript, Java
Frameworks
Express.js, Ember.js, Bootstrap 3, Jest, Cypress, React Native, Redux, Next.js, Electron, Tailwind CSS, Material UI, .NET, NestJS, Tauri
Paradigms
Asynchronous Programming, Promise, Responsive, Responsive Web Design (RWD), API/Services Architecture, Test Automation, DevOps, Functional Programming, Object-oriented Programming (OOP), Microservices, UI Design
Platforms
Linux, Amazon Web Services (AWS), Kubernetes, AWS Lambda, Harness, Blockchain, Ethereum, Vercel, Docker, WordPress, Safari, Windows, Amazon Linux, Azure
Storage
PostgreSQL, Hasura, Amazon S3 (AWS S3), NoSQL, Memcached, Redis, MongoDB, Amazon DynamoDB, Google Cloud, MySQL, ArangoDB, OwnCloud
Other
Ember CLI, APIs, Apollo, Back-end, Responsive UI, Full-stack, Admin Panels, Analytics, Full-stack Development, Third-party APIs, Responsive Design, UI Components, API Design, ESLint, API Integration, Web3, Artificial Intelligence (AI), Single-page Applications (SPAs), Front-end Development, Architecture, Code Generators, Cursor AI, WebSockets, Design Systems, Software Architecture, Agentic AI, AI Workflow, ChatGPT Prompts, Serverless, Ubuntu Server, GNU, Cryptocurrency Wallets, Payment APIs, CI/CD Pipelines, Single Sign-on (SSO), UI Libraries, Prompt Engineering, Large Language Models (LLMs), Solana, Startups, Cryptocurrency, Supabase, Front-end, Finance, Statistics, Graph Theory, Calculus, Algebra, Geometry, Optimization, Chrome Extensions, Browser Automation, PDF, Rendering, Windows Subsystem for Linux (WSL), HAProxy, Ethers.js, Crypto, PWA
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