Hendrik Wermser, Developer in Brunswick, Lower Saxony, Germany
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Hendrik Wermser

Verified Expert  in Engineering

Ruby on Rails Developer

Brunswick, Lower Saxony, Germany
Toptal Member Since
February 22, 2022

Hendrik was the main Ruby on Rails engineer in two different startups for 7+ years, in charge of all technology, including front end, back end, databases, CI/CD, cloud deployment, error and performance monitoring, logging, analytics, and A/B testing. In the past two years, Hendrik was a remote freelance team member for a SaaS startup, developing a proof-of-concept of a Flask, Python, and Vue.js application for use in hospitals. He has also taught a coding boot camp for the past two years.


Ironhack (Part-time)
JavaScript, Node.js, MongoDB, Express.js, React, Heroku, Netlify, Bootstrap
Ruby, Ruby on Rails (RoR), APIs, Docker, Vagrant, Ansible, Heroku, RSpec...
Ruby on Rails (RoR), Ruby, JavaScript, Backbone.js, Elasticsearch, Heroku...




Preferred Environment

MacOS, RubyMine, Slack, Git

The most amazing...

...project I've developed and deployed was a widget and the respective back end for a suite of web pages with 200 million weekly page impressions.

Work Experience

Lead Teacher, Web Development

2019 - 2021
Ironhack (Part-time)
  • Taught web development principles, tools, and best practices to aspiring web developers with the help of two teaching assistants.
  • Debugged students' projects and deployed each of them on Netlify and/or Heroku.
  • Kept teaching materials up to date and continuously improved their comprehensibility.
Technologies: JavaScript, Node.js, MongoDB, Express.js, React, Heroku, Netlify, Bootstrap

Principal Full-stack Developer

2015 - 2018
  • Developed a technology platform for shoppable content and smart home integrations as the principal engineer on the team. The application made recipe content shoppable at different online grocery shops. Avocando became part of Samsung Whisk in 2018.
  • Developed and maintained JavaScript snippets and widgets for integration with many third-party web applications and websites.
  • Set up and maintained all API integrations and ETL/data pipelines.
Technologies: Ruby, Ruby on Rails (RoR), APIs, Docker, Vagrant, Ansible, Heroku, RSpec, BrowserStack, Optimizely, A/B Testing, Let's Encrypt, JavaScript, Webpack, Capybara, Cucumber, Elasticsearch, SQL, Sidekiq, Redis, Fastly, ETL, Data Pipelines, APM, REST APIs, Web App Security, NoSQL, Ruby on Rails 5, Amazon Web Services (AWS), Amazon S3 (AWS S3), Google Analytics

Senior Full-stack Developer

2012 - 2015
  • Developed a price comparison application for grocery shopping as the main engineer on the team. Used linear optimization to compare prices across entire shopping carts, not just individual products. It had a RoR back end and JavaScript SPA front end.
  • Set up and optimized multiple Elasticsearch instances with language-specific customization.
  • Oversaw the entire deployment, performance and error monitoring, and continuous maintenance of the application.
Technologies: Ruby on Rails (RoR), Ruby, JavaScript, Backbone.js, Elasticsearch, Heroku, Vagrant, Ansible, New Relic, Sentry, SQL, PostgreSQL, Fastly, Varnish, Sidekiq, Redis, CI/CD Pipelines, Travis CI, Honeybadger.io, Git, GitHub, APIs, RSpec, Selenium, Agile, Kanban, Pivotal Tracker, REST APIs, Web App Security, Postman, NoSQL, Ruby on Rails 5, Amazon Web Services (AWS), Amazon S3 (AWS S3), Google Analytics

Junior Web Developer

2008 - 2011
i-sense Software GmbH
  • Developed customizations of the company's SaaS solution for different customers using mainly jQuery, PHP, and MySQL.
  • Developed and maintained custom XML helper libraries to help scale the customization process.
  • Monitored customers' installations and provided support and ad-hoc solutions during incidents.
Technologies: JavaScript, MooTools, jQuery, SQL, PHP, XML, XPath, CSS, HTML, MySQL

SaaS Prototype for Hospitals

A SaaS prototype for use in hospitals, based on Flask (Python), Vue.js, Docker, and Google Cloud Platform. Serving as a part-time developer, I collaborated with a front-end developer and a machine learning expert to research different options and setups for a future production application with cloud GPUs, deep learning, and 3D (VTK) capabilities.

Linear Optimization Library for Grocery Shopping

A Ruby implementation of a gem library to optimize grocery shopping using GNU Linear Programming Kit (GLPK). I was the sole developer on the project and defined and implemented an API for grocery shopping, specifically to optimize shopping carts using linear programming.

JavaScript Cross-origin Communication Library

A library to facilitate cross-origin communication for use in third-party widgets and snippets. As the sole developer, I built an easy-to-use API for this library to allow cross-origin remote procedure calls and websites to configure and control integrated third-party JavaScript snippets.

Simple Metadata Web Crawler Using Mitmproxy

A proxy-based app/CLI that allows simple crawling of websites and "recording" of the crawled metadata information. I was the primary developer and collaborated with another back-end developer to maintain the project and add features to expand the scope to more JavaScript-heavy target websites.
2010 - 2012

Master's Degree in Computer Science

Technical University Munich - Munich, Germany

2007 - 2010

Bachelor's Degree in Computer Science

Technical University Munich - Munich, Germany


Node.js, REST APIs, React, Backbone.js, Sidekiq, Vue, Puppeteer, Mechanize, Nokogiri, MooTools, jQuery


RubyMine, Slack, Git, Docker Compose, Postman, Google Analytics, Vagrant, Ansible, Sentry, Fastly, Varnish, Travis CI, Honeybadger.io, GitHub, RSpec, BrowserStack, Optimizely, Let's Encrypt, Webpack, Cucumber, Pivotal Tracker


Ruby on Rails (RoR), Ruby on Rails 5, Bootstrap, Selenium, Flask, Capybara, Express.js


Ruby, JavaScript, SQL, CSS, HTML, Python, PHP, XML, XPath, XQuery


MacOS, Heroku, Docker, Amazon Web Services (AWS), New Relic, Google Cloud Platform (GCP), Netlify


PostgreSQL, Elasticsearch, MongoDB, MySQL, NoSQL, Amazon S3 (AWS S3), Redis, Data Pipelines


ETL, Linear Programming, CSRF Protection, Agile, Kanban


APIs, CI/CD Pipelines, Computer Science, WebSockets, Web Security, Web App Security, APM, 3D, A/B Testing, Ruby Gems, CORS, Third-party Integration, Proxy Servers

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