Andreas Geffen Lundahl, Developer in Växjö, Sweden
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Andreas Geffen Lundahl

Verified Expert  in Engineering

Software Developer

Växjö, Sweden
Toptal Member Since
January 20, 2016

Andreas is a product-minded software engineer with a passion for startups. Equally invested in the product as he is in the code, Andreas strives for robust contributions that make both users and fellow developers happy. As a team member, he's eager to share knowledge, improve processes, and learn from his peers.


Jun Group
Elixir, Ruby, Ruby on Rails (RoR), JavaScript, React, Phoenix, PostgreSQL...
Joint Academy
Ruby, Ruby on Rails (RoR), TypeScript, Python, Go, PostgreSQL, React Native...
React, JavaScript, Node.js, Slate, GraphQL, TypeScript, Redux




Preferred Environment

Git, Emacs, Linux, OS X

The most amazing...

...thing I've built is a trading application for executing predefined strategies on the Swedish stock market.

Work Experience

Software Engineer

2022 - PRESENT
Jun Group
  • Extracted the audience part of their Ruby on Rails ad server to a separate service built with Elixir and Phoenix.
  • Scaled the capabilities of their audience to hold billions of targets while vastly improving both read and write performance.
  • Built a user interface for managing audience and segment data in the audience service.
Technologies: Elixir, Ruby, Ruby on Rails (RoR), JavaScript, React, Phoenix, PostgreSQL, Amazon Web Services (AWS)

Software Engineer

2021 - 2022
Joint Academy
  • Built the back-end part of Groups, the company's initiative to offer online support groups for patients.
  • Led the development of treatment switching, offering a better service for returning patients and ultimately increasing revenue.
  • Worked on the company's introduction to the US market, adapting the application for US compliance and billing.
Technologies: Ruby, Ruby on Rails (RoR), TypeScript, Python, Go, PostgreSQL, React Native, React

Software Engineer

2019 - 2021
  • Laid the foundation for the front-end architecture.
  • Built the core word processor with a custom layout engine, similarly to how Google Docs is implemented.
  • Forked Slate and added a functionality that was not easily supported in the off-the-shelf version, such as pagination.
Technologies: React, JavaScript, Node.js, Slate, GraphQL, TypeScript, Redux


2019 - 2019
  • Architected and implemented an MVP for a specific touchscreen use case.
  • Set the foundation for multiple areas of the project, such as the test suite and the Redux store.
  • Wrote a DB abstraction layer between PouchDB and the application.
Technologies: Electron, Redux, React, TypeScript, PouchDB


2019 - 2019
  • Helped modernize the eCommerce platform for Outnorth, one of Northern Europe's leading sites for outdoor equipment. Besides working on the architecture and implementation of the new platform, Andreas also worked with the in-house development team to improve internal processes.
Technologies: Amazon Web Services (AWS), PostgreSQL, Ruby on Rails (RoR), Ruby

Acting CTO

2017 - 2018
  • Led the development and improved the long-term vision for the product.
Technologies: Amazon Web Services (AWS), JavaScript, Ruby on Rails (RoR), Ruby


2017 - 2017
Undisclosed Trading Application
  • Architected and led the implementation of an application for stock traders. The application was built to facilitate the execution of certain strategies on stock markets.
Technologies: Electron, Clojure


2016 - 2017
  • Led the implementation of checkout flows, from Articulate's website to integrations with Stripe and Salesforce, and everything in between.
Technologies: Redux, React, JavaScript, Ruby on Rails (RoR), Ruby


2015 - 2016
  • Designed, architected, and implemented a completely new product.
Technologies: React, JavaScript, Java


2013 - 2014
  • Played a key role in modernizing the front-end architecture and implementing React for Fortnox, one of the leading business software providers in Sweden.
Technologies: React, JavaScript

Team Lead

2013 - 2013
  • Led a team for healthtech startup Kryapp. The work mostly consisted of building more features, such as a medical record system which passed a rigorous certification process.
Technologies: MongoDB, JavaScript, Ruby on Rails (RoR), Ruby


2013 - 2013
Multiple Swedish Public Transport Companies
  • Helped architect and implement a combined CMS and CRM for Swedish public transport companies. The systems developed are still daily used by hundreds of thousands of people.
Technologies: PostgreSQL, JavaScript, Ruby on Rails (RoR), Ruby


2012 - 2013
  • Helped architect the initial MVP.
Technologies: PostgreSQL, JavaScript, Ruby on Rails (RoR), Ruby

Team Lead

2012 - 2012
  • Led a team to build an MVP for a startup in healthtech. Besides leading a team of developers and designers, I was also responsible for initial architecture.
Technologies: MongoDB, JavaScript, Ruby on Rails (RoR), Ruby


2011 - 2012
Boss Media
  • Contributed to the development of customizable administrative panels for players.
Technologies: JavaScript, Ruby on Rails (RoR), Ruby


2011 - 2011
  • Contributed to the development of geographical tracking and visualization of trucks, time management for drivers, and more.
Technologies: Java, JavaScript, Ruby on Rails (RoR), Ruby


2009 - 2010
  • Helped one of Europe's leading name tag manufacturers to digitalize and improve their workflows by building internal tools and systems.
Technologies: Backbone.js, JavaScript, Java


Mapery is a collection of luxury map prints. Using a unique design method, we offer the most elegant and timeless map prints.

Prints from Mapery have sold worldwide, directly to consumers through the website, wholesale to brick-and-mortar stores, and on platforms such as Etsy.

Mapery has received over 600 five-star reviews.


Shopify API, Node.js, Stripe, Underscore.js, Backbone.js, React, Sidekiq, Etsy API, Normalizr, GitHub API, Auth0 API


Git, RSpec, GitHub, Amazon Elastic Container Registry (ECR), Redux Thunk, Gulp, Subversion (SVN), Adobe Photoshop, Adobe Illustrator, Apache ZooKeeper, AWS ELB, AWS CLI, Amazon Elastic Container Service (Amazon ECS), AWS Fargate, Amazon Virtual Private Cloud (VPC), Emacs, GIS, Amazon ElastiCache


Redux, Selenium, ClojureScript, Ruby on Rails (RoR), Electron, Phoenix, Relay, React Native


ECMAScript (ES6), Less, CSS3, ES7, Sass, CoffeeScript, HTML, CSS, Clojure, SQL, JavaScript, Ruby, TypeScript, Elixir, PHP, GraphQL, Python, Java, Go


Agile, Test-driven Development (TDD), Functional Programming, Distributed Programming, Scrum, Data Science


Shopify, Amazon Web Services (AWS), Docker, Amazon EC2, AWS Lambda, Linux, OS X, Salesforce


PostgreSQL, Amazon S3 (AWS S3), RethinkDB, MongoDB, Redis, Elasticsearch, PouchDB, PostGIS


Shopify Customizations, Web App Development, Etsy, Consul, User Experience (UX), Datomic, Customer Development, Business Development, Slate, Graphics

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