Andrei Kaleshka, Developer in Warsaw, Poland
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Andrei Kaleshka

Bio

Andrei is a seasoned web development expert with over 15 years of experience. The open-source software he's developed has been downloaded more than 4 million times worldwide. Although he's worked across a wide range of business domains, billing, payment, and accounting systems remain his primary areas of interest and expertise. Andrei brings strong capabilities in project implementation, management, and long-term maintenance.

Portfolio

Palladium Group
Ruby, Ruby on Rails (RoR), React, PostgreSQL, SQL, Heroku, Heroku Postgres...
WideFix
Business Development, New Business Development, Branding, Personal Branding...
NovoEd
Ruby on Rails (RoR), Ruby, Ruby on Rails 5, REST, SQL...

Experience

  • Ruby - 15 years
  • Ruby on Rails (RoR) - 15 years
  • React - 10 years
  • PostgreSQL - 10 years
  • Accounting Systems - 10 years
  • Online Classes & MOOCs - 10 years
  • Fintech - 10 years
  • Billing Systems - 10 years

Preferred Environment

Ruby, PostgreSQL, Fintech, React, Accounting Software

The most amazing...

...fact is that a single open-source library I created has been downloaded nearly 3 million times.

Work Experience

Software Engineer

2025 - PRESENT
Palladium Group
  • Implemented an API gateway for a third-party team from scratch.
  • Improved code in the mission-critical part of the system that reduced bugs the team struggled with for ages, and spent a lot of time on debugging and fixing the data.
  • Upgraded stack (Ruby/Rails/PostgreSQL) to current versions.
  • Resolved several critical and tricky bugs around the login page and having stock inventory out of sync.
  • Designed the architecture for app customization and expansion in global markets.
Technologies: Ruby, Ruby on Rails (RoR), React, PostgreSQL, SQL, Heroku, Heroku Postgres, GraphQL

Founder

2015 - PRESENT
WideFix
  • Built a strong team of software engineers, capable of delivering high-quality results.
  • Created a business strategy and personal branding site from scratch.
  • Managed successfully a team of around five software engineers.
  • Developed a competitive and cost-efficient financial model.
  • Established an effective business model that consistently delivers results.
Technologies: Business Development, New Business Development, Branding, Personal Branding, Personal Finance Management, Web Marketing

Senior Back-end Ruby on Rails Engineer

2025 - 2026
NovoEd
  • Replaced a missing team member for the period when the team had a lack of free hands to complete several urgent projects.
  • Extended existing functionalities around notifications to students with advanced filters for whom and when to send them.
  • Collaborated effectively with the team in the project: QA, CTO, and PM.
  • Added two recurring report generators with automatic upload to AWS S3.
Technologies: Ruby on Rails (RoR), Ruby, Ruby on Rails 5, REST, SQL, Amazon Web Services (AWS), JavaScript, React

Technical Lead Consultant

2025 - 2026
GRAFO AI LLC
  • Analyzed the current state of the development process through interviews with all team members, code review, reading docs, testing the product.
  • Streamlined development processes that boost speed and product quality.
  • Consulted the business owner on architectural decisions, team performance outcomes, and product evaluation, helping identify a faster and more cost-effective path forward.
  • Helped to find the right people for the project who are cost-effective and provide high-quality results.
Technologies: Ruby on Rails (RoR), React, Next.js, Code Review, Source Code Review, Vercel, APIs, Artificial Intelligence (AI), Team Leadership, Node.js

RoR Developer

2024 - 2024
Platform 21 Limited
  • Unblocked a completely stalled background jobs queue that was holding jobs processing third-party API calls.
  • Optimized a DelayedJob queue by redesigning job handling and dispatching, fully eliminating daily performance bottlenecks and queue stalls.
  • Improved application performance, eliminating recurring H12 errors on Heroku that previously occurred multiple times per day.
  • Added third-party integrations to the system, including Etsy, TikTok, Mailchimp, Awin, and Smiffys.
  • Fixed bugs in existing integrations with the system, including Xero, Kashflow, Clearbooks, QuickBooks, and Lightspeed (formerly Vend).
  • Added more functionalities to the existing and new integrations.
Technologies: Ruby on Rails (RoR), Heroku, Integration, Ruby, APIs, Accounting Software, Accounting Systems, PostgreSQL, Monitoring, Problem Solving, Message Queues, Queue Management

Senior React/RoR Full-stack Developer

2023 - 2024
Kajabi, LLC
  • Improved page load speed by 80 times. Used SQL to get rid of N+1 issues.
  • Added the vendors' directory page from scratch. That improved the app revenue by 100%.
  • Resolved several show-stopper bugs within just 1 hour.
  • Fixed numerous bugs throughout and implemented pagination, advanced search filters, and full-text search. These enhancements significantly improved the user experience and made the app more user-friendly.
  • Implemented several API endpoints for the new pages.
  • Introduced an authorization system into the app using a Pundit gem for that.
Technologies: Ruby on Rails (RoR), React, Stripe Connect

Music Website Developer

2020 - 2022
Worship Online Inc.
  • Rewrote the entire web version of the application.
  • Implemented a custom audio mixer player for the new site.
  • Developed a solution that allows moving the clients from the old site to the new one with no risks for the business. New clients grew by 90%, and the business increased its year-over-year revenue by 5% despite the financial crisis.
Technologies: Ruby on Rails (RoR), Wistia API, Music Streaming, Music, Stripe API, Docker, Ansible, Knockout (Knockout.js), SCSS, Sass, Slim, Elasticsearch, Redis, PostgreSQL, Sidekiq, Ruby on Rails 5, Ruby, Heroku, Next.js, Amazon Web Services (AWS), SQL, HTML5, CSS3, Web Development, Full-stack, HTML, CSS, Bootstrap, Ruby on Rails API, Online Classes & MOOCs

Senior Software Engineer and Team Leader

2020 - 2022
Hubstaff
  • Led a team responsible for customer support. The team reduced customer support requests two times, and its health metrics (according to office vibe) were above 9.0.
  • Brought good habits to the development department that improved application stability and code review quality, and drove an initiative to improve documentation.
  • Introduced fundamental design patterns into the code (business action, query object, serializers, etc.) to expedite development and reduce number of defects in the system.
  • Implemented back end for events happening in real time used by a live map on the front end.
  • Integrated a push notifications system to send real-time messages if users are at an interesting location on time.
  • Integrated Zapier so that customers could build their own workflows.
Technologies: Ruby, Ruby on Rails (RoR), PostgreSQL, Zapier, REST APIs, Heroku, SQL, API Integration

Ruby Consultant

2019 - 2020
Molinelli Media Group Sl
  • Integrated and maintained Stripe payment system to generate invoices and automatically charge clients.
  • Changed a single dropdown to multiple dropdown for the main entity in the application.
  • Improved speed of page based on PosgreSQL Full Text Search for 99% so that page loads for 300 ms instead of 30 seconds.
  • Implemented subscriptions functionality so that clients see what for they pay for and automated money collection is possible.
  • Expanded the service location from Spain only to UK + Spain.
Technologies: React, PostgreSQL, Stripe, Ruby on Rails (RoR), Ruby, Heroku, SQL, Billing Systems

Back-end Developer

2016 - 2019
Toptal
  • Integrated and maintained Stripe and PayPal payment systems, Intacct with the billing system, the invoicing system, and the accounting system.
  • Refactored a monolithic application so that it's ready for microservice architecture.
  • Extracted the billing domain to a separate service.
  • Implemented the new API using GQL for the new UI. It was also used for back-to-back communication.
Technologies: Billing, Accounting, Intacct, PayPal, Stripe, PostgreSQL, Ruby on Rails (RoR), Ruby, TypeScript, REST APIs, Heroku, SQL, Banking & Finance, Finance, Billing Systems, Fintech, SOLID Principles, Design Patterns, Payment Gateways

Ruby Developer

2016 - 2016
GobGob
  • Reduced bugs and failures around sophisticated booking rules in a hotel booking project.
  • Implemented custom packaging offers for bookings. That feature made the app more price-attractive for end users.
  • Made code 10x faster on one project by using SQL techniques instead of Ruby/Rails approaches.
  • Prepared the site for users working on the app in parallel by addressing race-condition issues that could corrupt the database.
Technologies: PostgreSQL, Elasticsearch, JavaScript, Ruby on Rails (RoR), Ruby, Heroku, Amazon DynamoDB, SQL

Team Leader

2014 - 2016
Mezuka, LLC
  • Created a very big application with complex business logic from scratch.
  • Built a team of software engineers capable of doing their job efficiently.
  • Made decisions on suitable technologies to implement a successful product and to achieve comfortable work for the developers and the product owner.
  • Integrated applications with numerous third-party services such as Authorize.net, Twilio, TaxCloud, eFax, and many others.
  • Implemented a complex system for displaying zip code areas on a map, enabling full-text search with filters by zip areas, calculating distance between coordinates, and performing other custom matchings and smart geolocation.
  • Implemented a single-page application with fully separated back-end and front-end parts.
  • Established development processes needed by the company.
  • Hiring and overseeing software developers for this project.
Technologies: NGINX, Jasmine, RSpec, Watir, Cucumber, Server Sent Events (SSE), RabbitMQ, Ansible, Elasticsearch, PostgreSQL, CoffeeScript, AngularJS, GrapesJS, Ruby, Heroku, SQL

Author

2013 - 2014
Packt
  • Wrote a book about Rake, which currently holds an average rating of 5.0 stars on Amazon.
  • Wrote the first and only book on Rake, establishing myself as a recognized advocate and evangelist for the tool.
  • Created a practical, step-by-step project featured as an example in the book.
Technologies: Rake, Ruby, Publishing, Ebook Writing, Technical Writing, Content Writing, Writing & Editing

Web Developer

2013 - 2014
Active Cloud
  • Built the architecture of a billing system that allowed it to scale the business by adapting to any client with minimum effort.
  • Built an RMS system from scratch for cloud resources and related entities.
  • Implemented APS package parsing and integrated it with the corresponding resources in the RMS.
  • Refactored nearly the entire application, eliminating a large amount of legacy code.
  • Improved project architecture by splitting models and controllers into modules (a.k.a. Rails Engines).
Technologies: JavaScript, Ruby, Ruby on Rails (RoR), PostgreSQL

Web Developer

2010 - 2013
Altoros Development
  • Supported numerous projects for this company, including Keenprint, AllProShipping, and CrossArts.
  • Learned English by taking free English courses provided by the company.
  • Took numerous business trips to the US, Norway, and England to meet with customers and project owners.
  • Improved the architecture of numerous Altoros projects, allowing for the removal of large amounts of legacy code.
  • Integrated a variety of payment systems into projects, including Authorize.Net, PayPal, and more.
  • Learned to implement multi-tenancy applications while working on the development of Keenprint.
  • Taught students. Read lectures and reviewed code using Gerrit.
Technologies: JavaScript, Ruby, Ruby on Rails (RoR), PostgreSQL

Web Developer

2009 - 2010
Synesis
  • Learned the Ext JS framework while creating a project module.
  • Learned the SOAP web service protocol while creating a project module.
  • Gained direct experience with code reviewing practices.
Technologies: JavaScript, Java

Network Administrator

2008 - 2010
BNTU University Dorm #4
  • Administrated a server running Debian OS for local network.
  • Learned and configured iptables in so way it allowed admins to ban network users on demand.
  • Created a local billing system using Rails, which allowed us to track user balance and ban them when it's zero.
  • Acquired an extensive understanding of network systems, including DNS, firewalls, and Unix systems.
Technologies: Shell, Ruby on Rails (RoR), Ruby

Software Engineer

2008 - 2009
BelHard
  • Dealt with billing systems and banking system formats.
  • Learned Python to be able to edit one of the project modules.
  • Extended the current functionality for processing bank transactions via FTP.
Technologies: Python

Web Developer

2008 - 2009
360 Media Group
  • Worked on 360.by, a project that was already part-way into the production process.
  • Observed how poor architecture can negatively impact a project.
  • Gained experience with using version control systems.
Technologies: Java

Experience

WorshipOnline

https://app.worshiponline.com/
This is a website that teaches playing musical instruments. Alone, I've managed to apply a new design to the site with a completely different stack of technologies on the front end. During the transition, the old UI and new UI worked in parallel. The transition has been made gradually to prove the new site works as expected with no business risks.

Compare the new site - https://app.worshiponline.com/ and the old site - https://classic.worshiponline.com/.

Toptal Clients

• Integrated and maintained Stripe and PayPal payment systems, the Intacct accounting system with the existing billing system, an invoicing system, and an accounting system
• Refactored a monolithic application so that it's ready for microservices architecture
• Extracted the billing domain to a separate service

Mezuka

SaaS application (B2C) for fast food stores and everyone.

Stack: Ruby, Grape, RESTful API, AngularJS, Cucumber, Rspec, Jasmine, RabbitMQ, PostgreSQL, Design Patterns, Twilio, Rails, Wkhtmltopdf, ImageMagick, Omni Auth, Elasticsearch, E Fax, Merchant Services, Delayed Job, TaxCloud, Amazon S3, Ansible, SSE (Server Sent Events), Google Maps API

ActivePlatform

https://activeplatform.com/
ActivePlatform is a full-service automated cloud brokerage platform that helps cloud providers, resellers, and distributors sell, provision, bill, and manage multi-vendor cloud services (SaaS, PaaS, IaaS) through a unified system with white-label stores and automation tools. It simplifies cloud delivery, billing, subscription lifecycle, and partner networks to boost efficiency and profitability.

Stack: Rails, XML, XPath, PostgreSQL, RSpec, TDD, Scrum, APS.

Blogging

https://widefix.com/blog
A personal blog where I share my experience and unusual solutions I've invented while working on my projects. This blog helped me become an author, and I wrote a book called "Rake Task Management Essentials."

Rake Task Management Essentials

The book I wrote, Rake Task Management Essentials, is a practical guide that covers the latest techniques in building, testing, and debugging Rake tasks to solve real-world automation challenges. The book starts with a basic knowledge of Rake, allowing you to solve repetitive tasks. Then it provides information on processes performed on files, which is crucial for understanding the tool's application.

Keenprint

http://keenprint.com
SaaS eCommerce application and order management system for commercial printers. This is a B2B2C platform developed from scratch. The clients of the app could order printing products from suppliers. The suppliers could manage the orders via the system and send using delivery services such as FedEx/UPS/USPS.

Stack: Ruby, Rails, Active Merchant, FedEx/UPS/USPS, jQuery, Ajax, RSpec, MySQL.

Fisikal

http://fisikal.com
Fisikal is a smart fitness and wellness platform focused on physical health, movement tracking, and performance improvement, helping users stay active, strong, and balanced through data-driven insights.

Stack: Ruby, Rails, jQuery, Ajax, SMS gateway, RSpec, MySQL.

Ruby Enums Gem

https://github.com/mezuka/enum
This is a very basic implementation of enums in Ruby. The cornerstone of the library is safety. The library was extracted out of Mezuka project I've been worked on before. We faced tech limitations while developing Mezuka and that make us to implement this Ruby extension on our own.

Migration Data Gem

https://github.com/ka8725/migration_data
This gem extends Ruby on Rails to make the development environment more comfortable. It allows you to safely write data migration code alongside standard Rails schema migrations in the same file, in a maintainable way.

I designed and developed this gem on my own to improve our team productivity when we had constant failures during database migrations. It allowed us to save tens of hours in total as a team weekly by preventing the issues with migrations.

As of now, the gem has been downloaded around 3,000,000 times.

Open Source Activity

https://github.com/ka8725
Contributed to a variety of open-source projects across the Ruby and Rails ecosystem, including GetOrBuild, Redmine S3, LocomotiveCMS, Twitter Bootstrap Rails, Devise, InheritedResources, Rails, MultiXML, DataGrid, couchbase-ruby-model, and others. Contributions included bug fixes, feature enhancements, documentation improvements, and community support, helping to advance the functionality, stability, and adoption of these widely used libraries and frameworks.

ActualDbSchema

https://widefix.com/db
I originally created this gem to boost my own productivity, and it now saves me up to 5 hours per week when working on Rails applications.

actual_db_schema is a Ruby gem for Rails that ensures your database schema remains consistent when switching between branches during development. It automatically detects and rolls back “phantom” migrations - those that were run in another branch but don’t belong to the current one - preventing errors and eliminating irrelevant diffs in schema.rb or structure.sql. I developed this gem entirely on my own as a unique solution with no analogues.

To date, it has been downloaded around 500,000 times.

Education

2018 - 2019

Certification in Computer Science

University of California San Diego - San Diego, CA

2005 - 2010

Bachelor's Degree in Automobile Engineer

Belarussian National Technical University - Minsk, Belarus

Certifications

DECEMBER 2026 - PRESENT

Microeconomics Principles Specialization

University of Illinois Urbana-Champaign | via Coursera

MARCH 2024 - PRESENT

Basic Statistics

University of Amsterdam | via Coursera

AUGUST 2019 - PRESENT

Mathematical Thinking in Computer Science

University of California | via Coursera

MARCH 2019 - PRESENT

Data Structures and Algorithms Specialization

University of California | via Coursera

Skills

Libraries/APIs

Stripe, REST APIs, Stripe API, Stripe Connect, Ruby on Rails API, React, Wistia API, Sidekiq, Node.js

Tools

Shell, Rake, Ansible, RabbitMQ, Cucumber, Watir, RSpec, NGINX, Sublime Text, Zsh, Git, Intacct, Zapier

Languages

JavaScript, Ruby, TypeScript, GraphQL, SQL, HTML, HTML5, CSS3, CSS, Java, Python, CoffeeScript, SCSS, Sass

Frameworks

Ruby on Rails (RoR), Ruby on Rails 5, Next.js, Bootstrap, GrapesJS, Jasmine, Ember.js, AngularJS, Knockout (Knockout.js), Slim

Paradigms

Object-oriented Programming (OOP), Design Patterns, Test-driven Development (TDD), Behavior-driven Development (BDD), Interactive Design, Software Testing, REST

Platforms

Heroku, Amazon Web Services (AWS), Docker, OS X, Music Streaming, Visual Studio Code (VS Code), Vercel

Storage

Elasticsearch, PostgreSQL, Redis, Amazon DynamoDB, Databases

Industry Expertise

Banking & Finance, Accounting, Bioinformatics

Other

SOLID Principles, Payment Gateways, Billing, Billing Software, Billing Systems, Full-stack, API Integration, Fintech, Domain-driven Design (DDD), Accounting Systems, Accounting Software, Web Development, Finance, Online Classes & MOOCs, Server Sent Events (SSE), PayPal, Content Writing, Technical Writing, Music, IT Automation, Problem Solving, Computational Logic, Computer Science, Algorithms, Critical Thinking, Data Structures, Graph Theory, Probability Theory, Data Visualization, Statistics, Market Research, Correlational Analysis, Business Psychology, Cost Accounting, Process Analysis, Behavioral Economics, Heroku Postgres, Programming, Theoretical Computer Science, Computer Programming, Network Analysis, Analysis, Engineering, Mechanics, Printing, Logistics, Exercise & Fitness, Fitness Trackers, Fitness Website Design, Sports, Cloud Computing, Digital Resources, Technical Reviews, Technical Research, Business Development, New Business Development, Branding, Personal Branding, Personal Finance Management, Web Marketing, Publishing, Ebook Writing, Writing & Editing, Integration, APIs, Monitoring, Message Queues, Queue Management, Cars, Code Review, Source Code Review, Artificial Intelligence (AI), Team Leadership

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