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Stefan Kölle

Senior Software Developer & Software Architect

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Senior Software Developer / Senior Software Architect

TENHIL GmbH & Co. KG (2025 - present)

• MCP-Server for ChatGPT Integration (2026) Built an MCP server for a major platform integration using Claude Code, from concept to production in 6 half-days solo. Full spec, Confluence documentation, Jira epics and stories, and PO artifacts fully generated within the same workflow.
• AI-driven Project Documentation (2026) Using Claude Code to generate complete project documentation end-to-end, including Confluence pages, Jira epics and stories, covering the full PO process without manual overhead.
• AI-Tooling Repository (2026): Built a structured AI-assisted development framework for the .NET team, providing reusable workflows for plan-and-implement processes, QA testing, and code reviews. Presented at internal Demo Day with full documentation.
• Regular presenter at internal monthly Demo Days, sharing AI tooling advances and new project outcomes with the engineering organization.
• Kubernetes Migration: All microservices are now running on Kubernetes, migrated to self-hosted Kubernetes on AWS machines.
• AI-assisted Development Workflow: Established a production-ready Claude Code workflow for rapid delivery, reducing time-to-production for new services significantly.
• Infrastructure Cost Optimization (2025) Reduced monthly infrastructure costs by €1,850 through strategic decommissioning of legacy systems and cloud routing migration, delivering ~€22,000 in annual savings.
• QA Automation Framework Built a scalable integration test system enabling continuous, code-based QA coverage growth and cross-codebase bug detection across multiple services.
• AI Workshop Organized and led an internal team workshop on AI-assisted search query parsing and natural language processing for job search optimization.
• Active Services Migration to Kubernetes (2025) Planned migration of active production services from legacy hosting to Kubernetes, including documentation and architectural concepts.
• Consistently delivering full-time output while working part-time, recognized across multiple product teams for high productivity and reliable delivery.
• Technologiestack: .NET Core, Kubernetes, Docker, TypeScript, Claude Code, OpenAI, Terraform, Sentry, Loki/Grafana.

TENHIL GmbH & Co. KG (08/2022 - 2024)

• OpenAI Integration (2024) Integrated OpenAI-based salary data generation into a multi-tenant microservice, enabling automated, AI-driven content enrichment at scale.
• Solely responsible for designing and building multiple core backend microservices end-to-end, including application services, geo data, feed generation, salary data, and email delivery integrations.
• Collaborating closely with the Product Owner to create and implement new services.
• Technologies: .NET Core 10, Docker, Azure, Terraform, Uptrends, Sentry, Loki, Quartz.NET.

Senior Software Developer / Senior Software Architect

stellenanzeigen.de GmbH & Co. KG (11/2018 - 07/2022)

• Architecting hosting solutions and migrating services to Azure.
• Implementing a CMS based on Squidex and managing server infrastructure.

Managing Director

Regio-Jobanzeiger GmbH & Co. KG (10/2014 - 12/2017)

Managing Director, CTO

stellenanzeigen.de GmbH & Co. KG (01/2011 - 10/2018)

• Reorganized the company, focusing on performance marketing and core products.
• Implemented the "SmartReach" performance marketing product.
• Significant projects: Multi-brand strategy, founding "Yourfirm" and "Regio Jobanzeiger", integrating "Kalaydo".

CTO, Member of Executive Management

stellenanzeigen.de GmbH & Co. KG (01/2004 - 12/2010)

• Led product management, software development, IT, customer service, and HTML ad creation.
• Introduced agile software development and virtualized all physical servers.

Head of IT / Development

stellenanzeigen.de GmbH & Co. KG (06/2000 - 12/2003)

• Developed a multi-client web frontend and restructured the ad creation process.

Web Developer

IXOS AG (05/1999 - 05/2000)

• Managed web development environment and internal departmental websites.

Education

FH Augsburg - Computer Science (1996 - 1999)

Internships

IXOS AG - Working Student (10/1997 - 04/1999)

• Redesigned the Jukeman website and prepared training rooms for R/3 training.

Personal Projects

Home Network Projects (2025-2026)

• Docker Host (Proxmox PVE)
  Virtualized Docker host with Debian 12.2 running containerized services including Portainer, Prometheus, Grafana, Gitea, monitoring exporters, and more. Full architecture documented on infra.moonweb.org.
• InfluxDB Time-Series Integration
  Deployed InfluxDB 2.x for sensor data collection from Tasmota smart plugs and HomematicIP thermostats, replacing older MySQL-based storage with modern time-series architecture.
• LED Matrix ESP32 InfluxDB Integration
  Data persistence layer for LED Matrix ESP32 sensor systems (DHT22 temperature/humidity) with InfluxDB 2.x backend. Automated collection at 60-second intervals for historical trend analysis.
• Air Quality Dashboard
  Dynamic HTML5 dashboard consuming real-time sensor data from InfluxDB via Flux query API. Displays temperature and humidity across all network locations, accessible via nginx reverse proxy.
• Tasmota Energy Monitoring
  Smart plug energy tracking with 8 Tasmota-enabled devices, integrating MQTT data collection and visualization. See also smarthome.moonweb.org.
• Network Hardware & Monitoring
  Four Zyxel GS1200-8HP managed switches in the server room, living room, and study, plus a Multi-WAN OpenWrt router for failover and VLAN segmentation. All switches feed into Prometheus monitoring via SNMP exporters, and IoT devices are isolated in VLAN 189.

Retro Computing (2022/2023)

• MiSTer and MiST FPGA Systems for preservation (see also retro.moonweb.org).
• DOS System, Amiga System, and Atari ST System with the environment from the early 90s.

Upgrade of old Atari Mega 4 (2021)

• Gotek Drive
• More RAM
• Alternative TOS ROMs
• SD HDD Adapter

Home Automation (since 2018)

• LED Matrix ESP32 for date, time, weather, and status messages via Web API, with a display in every room.
• MQTT for message transfer and remote control via Tasmota RF modules (433MHz).
• Power meter monitoring for washing machine and tumbler with info messages on LED matrices when finished.
• MP3 player with automated playback (e.g., bathroom radio when light is on).
• Raspberry Pi with pilight and RF433 module for remote control power plugs.

Various Docker Systems (since 2016)

• Monitoring: Prometheus, Grafana, InfluxDB, cAdvisor, Node Exporter, SNMP exporters
• Smart Home: Mosquitto MQTT broker, Home Assistant
• Infrastructure: Portainer, Nginx Proxy Manager, Authelia (SSO), Watchtower, Healthchecks
• Applications: Gitea (GitHub mirror), Stirling PDF, TubeArchivist, TubeSync, SearXNG

Walk-on Song (2019)

• When someone enters the office, their jingle is played.
• ESP32 scans WiFi, if a known device is found for the first time per day, the jingle is played.
• MP3 Module for playback on attached speaker.

Kids RFID MP3 Player (2018)

• Interactive audio playback system utilizing RFID technology.
• Powered by an Arduino Nano for compact and efficient operation.
• Plays specific audio files when RFID-tagged objects or cards are placed on the device.
• Customizable: users can upload and assign personalized audio content to RFID tags.

.NET Community Activity (2009 - 2011)

• Attended multiple .NET Open Spaces, including Ulm 2009 and Leipzig 2009.
• Developed a schema-less object storage system named StupidDB.
• Contributed to a developer blog with colleagues.
• Actively participated in Coding Dojos at AutoScout24.

Owner & Developer, inseco.de (2003 - 2008)

• Managed approximately 20 clients, primarily from the gastronomy and club sectors.
• Developed a CMS system for maintaining their websites, programmed in PHP and MySQL.
• Included modules for photo galleries, menus, and events.

Home Network Projects during IT Manager Phase (2000 - 2006)

• Set up a home network with various Linux servers and Windows NT 4.0.
• Implemented a predecessor to the pfSense firewall.
• Managed a FreeBSD server with Apache, Sendmail, and Perl scripts.
• Maintained an NT 4.0 file server.
• Administered Windows 98 and Windows 2000 hosts.
• More info at moonweb.org/network/

Mailbox/Fidonet (1994 - 2000)

• Operated a BBS and Fidonet Node (see also Networking & BBS on retro.moonweb.org).
• Managed a node in Augsburg with an uplink directly to the NC in Munich.
• Software was running on an OS/2 computer.
• Utilized 2x ISDN and 1x MODEM connections.
• Had about 20 subnodes and points.
• Served as the Bavaria HUB/HOST for various old networks.
• Developed several small software tools in Turbo Pascal for DOS.

PC Intro / Game / Software Development (1992 - 1994)

• Released Phobia Welcome Intro (Sourcecode/Picture/Video) for 486 PC in 1994.
• Released Tr@anceMission Intros (Sourcecode/Pictures/Videos) in 1992 and 1993.
• Developed Turbo Pascal Graphics Library X-Lib Unit (Sourcecode).
• Used Turbo Pascal and inline assembler for development.

Atari ST Software Development (1990 - 1992)

• Completed game 'Atom oh no' in 1992 (GFA Basic)

Programming Languages

AI-Assisted Development

I've fully embraced the AI-assisted development paradigm since early 2025. At work, I've taught Claude Code a workflow for handling Jira stories end-to-end: it evaluates requirements, provides feedback to the PO, and creates a detailed implementation plan. From there, it's mostly about supervising the plan while the code generation runs largely autonomously. For code review, we use a second AI (e.g., Codex) as a quality gate to catch issues that might slip through. In migration projects, I define the exact plan upfront and Claude Code executes it with increasing independence. The output gain is massive, delivering in a fraction of the time.

Privately, I work with OpenCode paired with OpenCode Zen, Merge Gateway, and OpenRouter, mostly for Python-based home lab and automation projects. See my GitHub projects for examples and the Dev VM setup for the infrastructure behind this workflow.

.NET Core

• Working with .NET Core since 2018 at stellenanzeigen.de GmbH & Co. KG, which became TENHIL GmbH & Co. KG in 2022, where I migrated the old VB and ASP-Classic applications to modern .NET Core.
• Built around a dozen microservices, including Jobs Per Mail, JobApply, GeoService, Feedexporter, and Salary Data Service, first hosted on Azure and built with Docker, Terraform, Azure Tables, Azure Blobs, S3 buckets, and PostgreSQL.
• Since this year, all of these microservices run in our self-hosted Kubernetes cluster on AWS machines.
• Introduced Squidex as a headless CMS for the microservice backend, with Sentry and Loki for monitoring and logging, and Quartz.NET, later Hangfire.NET, for scheduled jobs.

TypeScript

• Using Node.js privately for over a decade, TypeScript since its early days, and professionally at TENHIL since 2024.
• Since this year, TypeScript is my go-to for AI-built microservices.
• Built an MCP (Model Context Protocol) server for ChatGPT integration in 6 half-days using Claude Code.
• Implemented a TypeScript widget renderer for AI-driven applications with the OpenAI Chat Kit.

Python

• Working with Python since 2020 on private projects, home lab tooling, and automation scripts.
• Since this year, increasingly using Python for home network projects, with development accelerated by AI-assisted workflows in OpenCode.

.NET Framework

• As CTO at stellenanzeigen.de GmbH & Co. KG (2004-2010), drove the move from ASP Classic to the .NET Framework, replacing the monolithic setup with a layered architecture of SOAP web services.
• Hosted applications on Windows IIS with MSSQL as the database.
• Introduced TDD and DDD practices and shared that knowledge with the .NET community at OpenSpaces and CodingDojos.

PHP

• Developed a website CMS system (activetool.de) for multiple clients from 2003 to 2008.
• Created a PHP Ticketing System and worked with MySQL databases.

ASP-Classic

• Started with ASP-Classic on PC (Windows) in 1999 while working as a web developer at IXOS AG: managed the web development environment and built internal departmental websites, introduced search functions, request systems, and link checkers to optimize web servers, developed a Visual Basic application for generating static web pages, and designed a workflow for maintaining the website using ASP scripts and SQL databases.
• Led the IT and development department at stellenanzeigen.de GmbH & Co. KG from 2000 to 2003, migrating applications from idc/htx to ASP-Classic and developing a multi-client web frontend for newspaper publishers.

Java

• Began using Java on PC (Windows) in 1998.
• Participated in a Security Hash Team Project at iXOS Software AG, developing the Java frontend.
• Utilized development environments such as Kawa and IBM Visual Age.

C++

• First used C++ on PC (Windows) in 1997.
• Worked on an R/3 Integration Project during practical work at iXOS Software AG.
• Completed one semester of C++ on UNIX (Solaris) during studies in 1998.

PASCAL

• Started with PASCAL on PC in 1993, using TurboPascal 6.0, 7.0, and Borland Pascal 7.0.
• Developed DOSMENU, a menu system for DOS, and tools for Fidonet.
• Created two games: a Wheel of Fortune clone and a two-player Tetris.
• Studied PASCAL for one year in school (1994) and one semester on UNIX (Solaris) during studies in 1996.

Assembler

• Began learning Assembler on the Atari ST in 1992, creating simple programs with Pure Assembler, part of the Pure C Pack.
• Developed a small text mode demo with sound using DevPAK.
• Gained experience on PC in 1994, creating four demos using inline assembler in TurboPascal.

C

• First encountered C on the Atari ST in 1992, creating simple programs with Pure C, an advanced version of Turbo C.
• Completed one semester of C during studies in 1997.

BASIC

• Gained initial experience with BASIC on the EPSON HX-20 in 1988 and Atari ST in 1989.
• Developed two small games (Bowling, LiveStyleCity) using OmicronBasic.
• Created games such as AtomOhNo (an Atomix clone) and TOPchangethecolor with GFA-Basic and TOPpack.
• Produced graphic demos on the Atari ST around 1991.
• Developed simple programs using Amiga Basic in 1991.
• Studied BASIC for two years in school (1991-1992), including coding a Snake clone during class.

Legal Notice (Impressum, § 5 DDG)

Stefan Kölle
Neumarkter Str. 86c
81673 München

Phone/Fax: +49-(89)-20006547
E-Mail: [email protected]

Responsible for content according to § 18 (2) MStV: Stefan Kölle, address as above.

Full legal notice & privacy policy for this website and the moonweb.org network: hub.moonweb.org/impressum