Yannik Köllmann · Jena, Germany

Backend developer,
IDE plugin builder.

I build backend systems and developer tools — from scalable APIs in C# and ASP.NET Core to JetBrains IDE plugins that remove friction from daily workflows. Currently studying Computer Science at FSU Jena.

View Projects Resume Contact
C#ASP.NET CoreKotlinTypeScriptReactAstroUnitySQLJetBrains Plugin SDKGitHub Actions
Work

Products

All on GitHub →
cteXecutor ctexecutor.koellmann.dev
Execute and manage SQL Common Table Expressions step by step in IntelliJ IDEA and DataGrip. Automatic detection, visual highlighting, and keyboard-first workflow.
KotlinJetBrains SDKSQLDataGripIntelliJ
Sonarwhale sonarwhale.koellmann.dev
Test API endpoints without leaving your IDE. Discovers endpoints automatically from OpenAPI specs — supports ASP.NET Core, FastAPI, Spring Boot, and Express.
KotlinJetBrains SDKOpenAPIASP.NET CoreRider
Other Projects
SatTrak
Real-time 3D visualization of 12,000+ active satellites using Unity and Cesium. SGP4 orbit propagation via CelesTrak TLE data, GPU heatmaps, orbit rendering, day/night cycle. University project at FSU Jena — team of four.
UnityC#CesiumSGP4Unity Job System
Cryptborne
Top-down dungeon crawler in a medieval fantasy setting. Procedurally generated dungeons, diverse weapons with unique firing patterns, dynamic enemy AI, and low-poly KayKit assets. Built with Unity 6.
Unity 6C#Procedural Generation
Homepage / Portfolio
Portfolio site with a JetBrains Rider-inspired IDE interface — file explorer, tab system with drag-and-drop, fuzzy global search, configurable keybindings, dual view modes, and full i18n (DE/EN). Built with React 18 and Vite.
React 18TypeScriptViteTailwind CSSreact-i18next
more coming soon...
About
YK
Yannik Köllmann
Backend Developer & CS Student

I'm a software developer focused on backend systems and developer tooling. I trained as an IT specialist at monari GmbH — graduating as best trainee in Kreis Borken — and worked there as a full-time developer before starting my Computer Science degree at Friedrich Schiller University Jena in October 2024. I currently work remotely at monari GmbH alongside my studies.

My main stack is C# and ASP.NET Core for backend, TypeScript and Angular for frontend, and Kotlin for JetBrains IDE plugins. I also build things with Unity and occasionally work in Java and C++.

github.com/ykoellmann contact@koellmann.dev yannikkoellmann Jena, Germany
Tech Stack
C#ASP.NET CoreKotlinJavaTypeScriptAngularReactAstroTailwind CSSUnitySQLJetBrains SDKGitHub ActionsGitDockerC++

Most of my projects are open source. I enjoy building in public and sharing what I learn — whether that's a JetBrains plugin, a backend service, or a Unity game.

Resume

Resume

Experience
Working Student — IT Support
monari GmbH
Oct 2024 – Present
  • · Remote IT support alongside CS studies at FSU Jena
  • · Building cteXecutor (2.0.1, 300+ downloads) and Sonarwhale — JetBrains IDE plugins
  • · Building koellmann.dev as an Astro + Tailwind pnpm monorepo
IT Developer
monari GmbH
Jan 2024 – Oct 2024
  • · Full-time backend development with C# and ASP.NET Core
  • · Frontend development with TypeScript and Angular
  • · SQL database design and query optimisation
IT Specialist — Application Development
monari GmbH (Apprenticeship)
Aug 2021 – Jan 2024
  • · Graduated as best trainee in Kreis Borken (IHK Nord Westfalen, 2024)
  • · 1st Place IT Project Days 2023 — Project "PawPal" (web app for pet adoption)
  • · Backend development with C# and ASP.NET Core
Awards
Best Trainee — IHK Nord Westfalen
Kreis Borken · 2024
1st Place — IT Project Days 2023
Project "PawPal" · BKW Ahaus
Education
B.Sc. Computer Science
Friedrich Schiller University Jena
Oct 2024 – Sept 2027
IT Specialist — Application Development
Berufskolleg Wirtschaft und Verwaltung Ahaus
Aug 2021 – Jan 2024
Skills
Backend
C#ASP.NET CoreKotlinSQL
Frontend
TypeScriptReactAstroTailwind CSS
Tools & Platforms
JetBrains SDKUnityGitHub ActionsDocker
Activity

GitHub

github.com/ykoellmann
Contact

Let's talk.

Have a project in mind, a question about one of my plugins, or just want to say hi? I'm happy to hear from you.

Send a message Open an issue
Email
contact@koellmann.dev
GitHub
github.com/ykoellmann
LinkedIn
yannikkoellmann
Location
Jena, Germany