Career Profile

I’m a Senior Software Engineer with more than 10 years of experience in designing, developing, and maintaining software systems on various platforms. In my most recent role, I built scalable distributed services for a no-code SaaS platform where I technically led the development efforts of the product’s integrations platform. I’m a JVM expert and a self-appointed Kotlin enthusiast. I have been acting as a mentor in different roles to support other people get better at their craft. I have conducted a few hundred technical interviews throughout my career and taught dozens of people to do the same. I enjoy working on both end-user and developer-facing products and APIs and care a lot about software and team quality in general. Right now, I work as a contractor for Karat where I act as a technical interviewer, mentor and content creator.


Freelance Senior Software Engineer and Consultant

since 08/2022
Simon Wirtz

I work with multiple clients on a contract basis to help them accelerate their business. Most of my work is related to backend software engineering (specialized in Java, Kotlin, Spring, microservices and cloud based products). I have been a Kotlin expert since 2017 and helped multiple groups learn the language. In addition, I have been conducting technical interviews for my clients to provide a fair and objective experience to the candidates. As part of my involvement in interviewing, I have also been a content developer in this field and help my clients create new relevant technical tests and interview formats.

Senior Interview Engineer and Mentor (Freelance, Remote)

since 04/2018
Karat, Seattle (USA)

I work with Karat as a freelance Interview Engineer where I conduct technical interviews for well-known tech companies in the US, Europe and other parts of the world. This work involves designing and mastering algorithmic coding challenges to support our candidates during remote interviews. The candidate’s performance is evaluated and documented in each interview. I joined Karat’s mentoring team in 2019 where I onboard new interviewers to the platform and ensure continuous improvement and consistency by guiding and working closely with other interviewers. At Karat, I also act as a content creator who has worked on multiple question sets where I designed and tested new questions for our interviews.

Senior Software Engineer (Remote)

08/2019 - 08/2022
BRYTER GmbH, Berlin (Germany)

At BRYTER, I designed and implemented an integrations platform for the main product, a SaaS no-code platform. The integrations platform was based on a Serverless approach where we used tools like Kubernetes, Docker, OpenFaaS, Prometheus, DataDog, Kotlin and a few more. We maintained hundreds of different integrations, an SDK for developers to use and the API to talk to integrations from within the main product. I was on this team since the beginning and hired and onboarded multiple new team members. I actively contributed to creating and shaping OKRs for the team and helped create our product metrics that helped with tracking our objectives. At BRYTER, I contributed to company-wide technical alignment and improvement efforts from the start and saw the company grow from 30 to around 230 people.

Senior Software Engineer (Remote)

07/2018 - 07/2019
Exactag GmbH, Düsseldorf (Germany)

We developed a big data visualization tool for a multi-tenancy SaaS product. I built a generic SQL query framework with Kotlin, jOOQ and Spring that enabled sophisticated data fetching capabilities through a REST API. We consumed this API from multiple UIs written in React. One of the main challenges involved finding a good abstraction level and making the SQL querying as dynamic as possible. Part of my work was also mentoring the team on Kotlin. I worked in a distributed engineering group of 5 people.

Software Developer

08/2014 - 06/2018
n-design GmbH, Cologne (Germany)

Full stack development with Java, Kotlin, Spring, OSGi, AngularJS, REST, SOAP and more. I held the temporary role of a technical team lead. The product played an important role in a domestic e-health infrastructure rollout for which we provided the device that acted as an entry point to this secure private infrastructure. My work involved security topics, card reader communication, service orchestration and more. I was, among other things, also responsible for onboarding new team members, participating in software architecture discussions and improving our release management.

Apprentice and Junior Operations Internal Developer

09/2011 - 07/2014
TravelTainment GmbH, Aachen (Germany)

Full stack development with Java, OSGi, Spring, Hibernate, MySQL, MongoDB, JavaScript and other web technologies. We built a monitoring application that provided an overview of multiple internal systems of the company that served the operations team with an overview of the overall system’s health. The work to enable these monitoring capabilities involved integrating with a couple of other systems in the infrastructure, extracting data from it to transform it into reasonable metrics we could display in the application.

Tools and Languages

A summary of tools that I have learned to work with over the years:

Languages - Kotlin, Java, JavaScript/TypeScript, Go, Python, SQL, HTML, Bash
Containers and orchestration - Docker, Kubernetes, OpenFaaS
Tooling - Jetbrains IDEs, GitLab, GitHub, Jenkins, YouTrack, Travis
Engineering methodologies - Clean code, Agile, Empowered product teams, TDD, Scrum, CI/CD, DevOps
Engineering areas of interest - API design, SDK development, Performance tuning, Cloud-native applications, Distributed Systems, Serverless/FaaS architectures

Skills & Proficiency

Kotlin, Java, JVM

Kubernetes, Docker and ☁️

SQL and Databases

API and SDK Design


Technical Writing

Content Creation


Node.js and popular UI frameworks


Resources that I published or contributed to:

Medium blogging
I’m an active blogger on Medium, follow me here
StackOverflow contributor
I’m a contributor on StackOverflow, follow me here
Devoxx UK: Diving into advanced Kotlin features
A presenation on advanced Kotlin features, available on Youtube
Droidcon NYC: Diving into advanced Kotlin features
A presenation on advanced Kotlin features, available on
Getting Started With Kotlin - DZone RefCardz
A guide for beginners with the Kotlin programming language, available here
Using Kotlin with Ktor to create Web Apps - DZone Web Development Guide
A guide about Kotlin web development with Ktor, a popular web toolkit, available here
Null-Safe Programming: The Kotlin Way - DZone Java Guide 2018
A guide about Kotlin’s nullability features compared to Java, available here