David is available for hire
Hire DavidDavid Gero
Verified Expert in Engineering
Back-end Developer
Szeged, Hungary
Toptal member since March 10, 2023
Bio
David is an experienced, self-taught Ruby and Ruby on Rails developer who started his career in computational linguistics nearly a decade ago. Initially, he worked on different NLP projects but soon focused on web application development. David has worked across multiple industries, such as eCommerce, education, business technology, and procurement, and he has even created his own profitable app.
Portfolio
Kör Zrt
Ruby on Rails 6, Ruby on Rails 7
Fressnapf
Shopify, Shopify API, Shopify Plus, Shopify Payments
Toptal
Ruby, Ruby on Rails (RoR), Docker, GraphQL, Redis, PostgreSQL, Sidekiq
Experience
- Ruby on Rails (RoR) - 10 years
- Ruby - 10 years
- Python - 6 years
- Pandas - 5 years
- Linux - 5 years
- Shopify - 5 years
- Generative Pre-trained Transformers (GPT) - 4 years
- Computational Linguistics - 4 years
Preferred Environment
Linux, MacOS, Ruby, Python, Shopify
The most amazing...
...thing I've done was founding a startup following the customer development methodology. I've presented pitches and sold the app before building it.
Work Experience
Senior Ruby on Rails Developer
2024 - 2026
Kör Zrt
- Developed and maintained features of the company’s platform, focusing on stability and GTM.
- Collaborated closely with product and operations teams to translate business requirements into maintainable technical solutions.
- Took ownership of complex features and delivered them end-to-end in Ruby on Rails.
Technologies: Ruby on Rails 6, Ruby on Rails 7
Shopify Consultant & Developer
2023 - 2023
Fressnapf
- Acted as technical lead for two Shopify subscription stores. I was responsible for development, system design, and technical consulting.
- Built the subscription and billing infrastructure, connected external tools, and set up the operational workflows.
- Implemented automated email flows for onboarding, engagement, and customer retention.
Technologies: Shopify, Shopify API, Shopify Plus, Shopify Payments
Back-end Engineer
2022 - 2023
Toptal
- Worked as a core developer in the improvement of Toptal's recruiting processes using Ruby on Rails.
- Implemented new features and ran A/B tests to fine-tune the different business processes.
- Added new tasks and maintained older ones to smooth the overall recruiting experience.
Technologies: Ruby, Ruby on Rails (RoR), Docker, GraphQL, Redis, PostgreSQL, Sidekiq
Founder and Developer
2020 - 2022
Tezisto
- Launched the Product Passage App in the Shopify App Store to help companies increase sales through the major Hungarian product and price comparison site.
- Led the business development process following the customer development methodology. Conducted interviews, wrote and presented pitches, managed operations from start to finish, hired specialists, and led incremental improvements.
- Helped, as a Shopify expert, over 30 stores automate logistics and data synchronization processes to run their businesses as smoothly as possible.
Technologies: Ruby, Shopify, Ruby on Rails (RoR), React, Heroku, Shopify API, Shopify Theme, Shopify Payments, PostgreSQL, GraphQL
Ruby on Rails Developer
2020 - 2021
Fuse Universal
- Created a custom learning platform with Ruby on Rails for B2B clients, helping to share knowledge and expertise within their companies.
- Handled custom integration with Auth0, a fully managed authentication and authorization service to increase security and portability with the clients' systems.
- Added new features and maintained old ones while creating multiple microservices and running them on their own servers or as a serverless solution like AWS Lambda in Ruby and Node.js.
Technologies: Ruby, Ruby on Rails (RoR), Python, Pandas, Amazon EC2, Capistrano, MySQL, Auth0, RSpec, Docker
Ruby on Rails Developer
2019 - 2020
Purchasing Platform Inc
- Created a custom B2B procurement and eCommerce platform with Ruby on Rails and Go for the manufacturing housing industry.
- Provided data-driven suggestions that helped stakeholders make better decisions in defining resource requirements.
- Built multiple microservices from the monolith Ruby on Rails application in Ruby and Go.
Technologies: Ruby, Ruby on Rails (RoR), Linux, Go, Bash, Amazon EC2, Ansible, Capistrano, PostgreSQL, RSpec, Capybara
Search Engineer
2017 - 2018
Cookpad
- Testimonial: "There are 100 million people on average in more than 70 countries with over 30 languages using Cookpad every month."
- Worked as a search engineer at Cookpad, a recipe-sharing platform.
- Created and maintained the language pre- and post-processing in Ruby and Python, which was used for indexing millions of recipes in different languages on ElasticSearch.
- Implemented language model editors on Ruby on Rails to fine-tune language models and improve the search experience.
Technologies: Ruby, Ruby on Rails (RoR), Python, Elastic, Generative Pre-trained Transformers (GPT), Natural Language Processing (NLP), Docker, Amazon EC2, Bash, Pandas, PostgreSQL, Redis, Sidekiq
Software Developer
2016 - 2017
Analogy
- Created a semantic search engine and automated semantic graphs in English and Hungarian language for tax advisors to speed up the searching, finding, extracting, and comparing millions of tax documents.
- Built the web application in Ruby on Rails and the NLP data pipeline in Python and connected the different parts of the system with RabbitMQ (message bus).
- Handled machine learning with SciPy and Scikit, data analysis with NumPy and Pandas, and NLP with NLTK and spaCy.
Technologies: Ruby, Ruby on Rails (RoR), Python, Natural Language Toolkit (NLTK), SpaCy, Pandas, RabbitMQ, Natural Language Processing (NLP), Generative Pre-trained Transformers (GPT), Bash, Ansible, Docker, Amazon EC2, RSpec, Capybara, PostgreSQL, Redis, Neo4j
Ruby on Rails Developer
2013 - 2015
Red Steed Studios Kft
- Created a web application and API using Ruby on Rails for Bitcoin and Stellar cryptocurrency ATM and mobile application.
- Progressed from being the first developer to being part of a growing team of 10 people, including mobile app developers, testers, and back-end developers.
- Reported directly to the stakeholders as part of my role.
- Kept the design flexible due to the multiple changes in the base cryptocurrency.
Technologies: Ruby, Ruby on Rails (RoR), Heroku, Google Protocol Buffer, Stellar SDK, Bitcoin, Fintech, PostgreSQL, RSpec, Capybara
Experience
Product Passage
As a founder of the app, I conducted market research, pitched, copywrote, sold, built, developed, maintained, and supported the whole application. At the same time, I hired external experts to update different parts of the system.
Stocks in The Future – Education
https://github.com/rubyforgood/stocks-in-the-future• Acted as one of the main contributors to the Stocks in the Future Rails codebase, delivering key features and improvements used by volunteers and partner organizations.
• Implemented new application functionality and fixed bugs while maintaining a high standard of code quality and test coverage.
• Collaborated with community contributors across time zones to review pull requests, shape project direction, and refine the development roadmap.
• Implemented new application functionality and fixed bugs while maintaining a high standard of code quality and test coverage.
• Collaborated with community contributors across time zones to review pull requests, shape project direction, and refine the development roadmap.
Education
2008 - 2014
Bachelor's Degree in Hungarian Expert and Language Technolog
University of Szeged - Szeged, Hungary
Certifications
MARCH 2023 - PRESENT
Mastering Value Propositions
Strategyzer
OCTOBER 2020 - OCTOBER 2021
App Development Certification
Shopify Partner Academy
MAY 2016 - APRIL 2017
Inbound Sales Certification
HubSpot Academy
Skills
Libraries/APIs
Pandas, Natural Language Toolkit (NLTK), SpaCy, Sidekiq, React, Shopify API
Tools
Elastic, RabbitMQ, Stellar SDK, Ansible, Capistrano, RSpec, Auth0, Shopify Plus
Languages
Ruby, Python, Go, Bash, GraphQL
Frameworks
Ruby on Rails (RoR), Google Protocol Buffer, Capybara, Ruby on Rails 6, Ruby on Rails 7
Platforms
Shopify, Linux, Heroku, Docker, Amazon EC2
Storage
PostgreSQL, MySQL, Redis, Neo4j
Other
Computational Linguistics, Natural Language Processing (NLP), Web Marketing, Sales, Tech Sales, Bitcoin, Fintech, Shopify Theme, Shopify Payments, Value Proposition, Value Proposition Design, Generative Pre-trained Transformers (GPT), Ruby on Rails 8
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