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Jonas Fackelmeyer

Web. Mobile. To the cloud.

I build web and mobile products and take responsibility for databases and infrastructure.

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Full-stack engineer · Hagen, Germany

TypeScript / React / Node.js

Workflow illustration · synthetic data

Illustrative workflow: a phone recognises Demo-Artikel 001 from a barcode; a web ordering list beside it shows two sample items. The example interface is in German.

From a scan in the OR to the cloud.

My scope: web · mobile · database · infrastructure

Read the case study

Independently designed example interface; not a customer screen.

Selected work

All projects
Illustrative reconstruction of the Illuminate menu showing Boosting 1.60×, brightness slider, display information, Method and Pause Boost.
Menu illustration based on the original

Illuminate

Native macOS app

Extra brightness for XDR displays. Native Swift, AppKit and Metal – finished and in my daily use.

The default overlay disappears with the app. No modified system state is left behind.

$ git commit --no-verify

Blocked

Checks must not be bypassed.

guard → review → commit
Simplified guard example

agentic-workflow

Open source · Claude Code plugin

My rules for coding agents as a plugin. A guard hook blocks bypassed checks and asks before sensitive changes.

A guardrail, not a sandbox. Every diff still needs my review.

Why I removed a layer again.

Two developers, three runtimes. The additional Spring BFF had become little more than a proxy. I proposed removing it.

Read about the decision
Portrait of Jonas Fackelmeyer
open to opportunities

About me

I’m Jonas. I like building things myself – and questioning what a product really needs.

My professional background is in IT security and hospital software. I also develop smaller software projects on a self-employed, part-time basis. Working in small teams taught me to make decisions beyond an individual screen and take responsibility for their consequences.

More about me and my background

Career

From IT security to web, mobile and infrastructure.

2021today

  1. Founding EngineerOrthoOS

    Multi-tenant practice management platform for orthodontic practices; as co-founder, responsible for the entire technical side.

  2. Part-time self-employmentJonas Fackelmeyer | Software Entwicklung

    Development of smaller software projects.

  3. Full Stack Web Developerclinicpartner eG

    Digital platform of one of the largest purchasing cooperatives in German healthcare; features end to end, from database to mobile app, including the migration of a Java application from JDK 17 to 25.

  4. Apprenticeship as IT specialist for application developmentISL Internet Sicherheitslösungen GmbH

    German vocational training (Fachinformatiker für Anwendungsentwicklung), focus on IT security.

Green tests. Wrong server.

The browser tests passed. But I spotted the development toolbar in the screenshots: the tests had checked the running dev server instead of the finished build. They now use a dedicated port and never reuse an existing server.

My review process and its limits
Schematic comparison of two browser windows: both tests pass. On the left, a highlighted development toolbar reveals the dev server on port 4321; on the right, the finished build runs on port 4329.
Illustrative reconstruction: both tests pass. Only the right one checks the build.
Expected
Tests against the finished build
Spotted
Development toolbar in the screenshot
Fixed
Dedicated port · reuseExistingServer: false

Let’s talk.

A role on your team, a smaller project or a technical question: I’d be happy to hear from you.

Jonas Fackelmeyer

Hagen, NRW

open to opportunities

Write a messagejonas@fackelmeyer.com