Leif Gensert, Developer in San Diego, CA, United States
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Leif Gensert

Verified Expert  in Engineering

Software Developer

San Diego, CA, United States
Toptal Member Since
February 14, 2018

For the past eleven years, Leif has worked as a full-time developer focusing on back-end development utilizing Ruby or Elixir. He's worked for giant consulting firms and newly founded startups. Through side projects and open source contributions, he makes sure he stays up to date on the latest tech. A healthy sense of pragmatism keeps him grounded to choose the technology that makes sense as opposed to going with whatever is hip right now.



Preferred Environment

Tmux, Git, Visual Studio Code (VS Code)

The most amazing...

...side project I've released is HN Vanity: an event-sourced application for getting basic hacker news statistics.

Work Experience


2018 - PRESENT
Tata Steel DV
  • Scoped, planned and implemented new features to an internal application.
  • Delivered a massive integration change with Zoho Books.
  • Integrated Hubspot CRM.
Technologies: PostgreSQL, Heroku, Ruby


2018 - 2018
Blend Media
  • Supported the development of new features.
  • Came up with a new concept for the publishing pipeline of 360° videos.
  • Successfully integrated the product with Salesforce Pardot.
Technologies: PostgreSQL, Elixir

Freelance Developer

2017 - 2017
QT Mobilitätsservice GmbH (Qixxit)
  • Introduced a new CI pipeline to improve deployment processes and regression tests.
  • Built an automated acceptance test suite to give product department a better overview of the state of development.
  • Implemented a proof of concept for a routing engine based on pgRouting.
Technologies: pgRouting, Docker, Neo4j, PostgreSQL, Elixir

Freelance Developer

2016 - 2017
solarisBank AG
  • Implemented a database anonymization program for efficiently creating test data.
  • Improved the existing continuous integration process.
  • Created a notifications feature in the core applications that sent out messages via WebHooks.
  • Worked on a prototype for a core banking system built in a CQRS way.
Technologies: Docker, PostgreSQL, Apache Kafka, Elixir, Ruby

Senior Developer

2013 - 2016
Propertybase GmbH
  • Designed and implemented a periodical import tool to fetch listing data in different formats (JRuby).
  • Implemented and maintained the lead generation tool while working closely together with customer success and sales teams to further adapt the tool to new inbound channels.
  • Handled and managed the technical onboarding of new clients (including data migration to Salesforce).
Technologies: Salesforce, Redis, MongoDB, PostgreSQL, JRuby, Ruby on Rails (RoR), Ruby

Senior Developer

2011 - 2013
stylefruits GmbH
  • Maintained and improved the main application (Ruby on Rails).
  • Developed a URL-shorting service (Sinatra on JRuby).
  • Designed and implemented a back-end to manage language translation tokens (Sinatra).
  • Managed and handled the weekly testing process—writing automated scripts and overseeing the manual testing sessions.
Technologies: MySQL, Redis, Ruby on Rails (RoR), Ruby

Senior Software Engineer

2008 - 2011
  • Improved and maintained a Java-based web application for Deutsche Telekom AG (OMS-IP).
  • Led workshop lessons regarding knowledge transfers for an offshore team in Kolkata, India.
  • Maintained an invoicing system for a satellite TV provider in Munich.
  • Improved an internal continuous integration workflow by dynamically dispatching test cases to concurrent processes.
Technologies: Oracle, Java


2005 - 2008
Process Innovation Ag
  • Developed for the web with Java and JSP.
  • Worked on IMB Lotus Notes and IBM DB2 development.
Technologies: Lotus Notes, JEE, Java

HN Vanity

An event-sourced application that monitors Hacker News and extracts basic statistics for every story.

The statistics include:
• Title change
• First hit of the front page
• The time it took to hit the front page
• The highest front-page position
• The total time spent on the front page

Implemented with Elixir and PostgreSQL as an event store.

Release Ping

An overview of the common programming languages and their latest versions (stable and unstable).

How Playing Around with Experimental Technologies Landed Me A 6-month Freelance Gig

An article about my experience building a side project; it has over 9,000 views.


A library that provides a DSL to transform data structures which is very valuable when working on data migrations.


A Microsoft Excel parser that was written in Elixir.


A Ruby gem to access the Salesforce Bulk API.


A Salesforce Formula parser that was implemented in pure JavaScript.


This backports newer functions to older versions of Elixir.

PostgreSQL S3 Backup Docker Container

A useful docker container that backups PostgreSQL databases to S3 and makes it possible to restore them.

So So Soccer

A comparison project between event sourcing and CRUD to solve the same problem: convert a soccer result table into an end-of-the-season standing table.

Elixir Docker Image

A minimal Elixir docker image.

Time Tracking

I wrote a script to synchronize Toggl time entries with FastBill.
2005 - 2008

Bachelor's Degree in Computer Science and Business Administration

DHBW Karlsruhe - Karlsruhe, Germany

2005 - 2008

Bachelor's Degree in Computer Science

The Open University - London, England


pgRouting, Salesforce API, Salesforce Bulk API, Salesforce REST API, React


Git, Tmux, Lotus Notes


Ruby on Rails (RoR), Phoenix


Ruby, Elixir, JavaScript, Elm, Java, JRuby


REST, CQRS, Event Sourcing


Salesforce, Visual Studio Code (VS Code), Oracle, Apache Kafka, Docker, Heroku, JEE


Redis, PostgreSQL, MySQL, MongoDB, Neo4j



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