Zügel Just Learned Python

Alexander von Zitzewitz Leave a comment

With our newest 26.4.1 release of the Zügel MCP server we added Python as a second supported language after. This article only explains the Python setup and Python specific features. If you want to learn what Zügel is and what it can do for you, please read our introduction article.

Python Setup

As described in the introduction you need to create an .mcp.json file that tells your agent how to start Zügel. Then start your agent in the root directory of your Python project and ask it to use the generate_config tool to generate the zugel.json file followed by a call to reload_all. After that the agent load the will analyze your project and create the initial baselines. It will inform you about existing cyclic dependencies on the file and directory/package level. If you add architecture definition files it will also check your architectural rules.

The Python version of zugel.json looks like that: 

{
  "language": "python",
  "project": {
    "modules": [
      { "name": "widget", "sourceRoots": ["src"] }
    ],
    "generatedPatterns": ["**/*_pb2.py", "**/*_pb2_grpc.py", "**/generated.py"]
  },
  "arcFiles": ["architecture/Widget.arc"]
}

The configuration for tolerated cyclic dependencies is the same as in Java. To mark generated code you can provide a list of patterns that match generated Python files. This is relevant for cycle analysis. Cyclic dependencies only consisting of generated files are tolerated automatically.

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Meet Zügel – An MCP Server Giving Your AI Coding Agent An Architectural Conscience

Alexander von Zitzewitz Leave a comment

How Zügel keeps agent-written code inside your intended architecture — and helps you dig out of the debt you already have.

This article covers the version 26.4.1 (released on Aug 20th 2026) of Zügel.

AI coding agents have changed the economics of writing code. They have not changed the economics of structure. An agent will happily add the fifteenth dependency from your persistence layer back into your UI, import an internal class from a subsystem that was never meant to expose it, or close a dependency cycle that fuses two modules into one inseparable blob — all while the tests stay green. Architecture erosion used to happen at human speed. Now it happens at machine speed. Zügel – the German word for rein – is designed to stop that from happening. It puts you back in control and directs the coding agent to write architecturally and structurally sound code.

The traditional answer — periodic architecture reviews, static-analysis gates in CI — catches the damage after it is written. That is too late for agent workflows: by the time CI complains, the agent has already built three features on top of the illegal dependency.

Zügel moves the check to the moment that matters: before the agent writes the dependency. It is an MCP (Model Context Protocol) server that any MCP-capable agent — Claude Code, or anything else that speaks the protocol — connects to like any other tool provider. Under the hood it:

  • parses your sources itself (Java only Today with more languages coming soon),
  • maintains architecture rules based on a subset of Sonargraph’s architecture DSL (optional),
  • computes violations and dependency cycles from the resolved model,
  • tracks every change against baselines, so progress and regressions are visible per edit, and
  • answers precise dependency questions the agent would otherwise (badly) approximate with grep.

Zügel is a companion to Sonargraph, and can be used independently from it. Using it together with Sonargraph will still provide extra benefits like CI integration, dependency visualization and a powerful environment to design architecture rules based on the Sonargraph architecture DSL.

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Major Changes to our C/C++ System Model

Alexander von Zitzewitz Leave a comment

When we added C/C++ to Sonargraph our work was heavily influenced by John Lakos famous book “Large Scale C++ Design”. In this book Mr. Lakos presented a solid system to define the architecture of C++ systems based on components. A component in the most simple case is the combination of a header file and a source file, e.g. User.h and User.cpp. The header declares all elements that can be used from outside of the component, while the source file contains the implementation of the functionality. This unites the header and the source file into a logical component, that is better suited for dependency analysis.

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ArcTree Tutorial

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Free Trial and Licensing

ArcTree is a plugin for IntelliJ IDEA that visualizes code dependencies for Java and Kotlin projects in a unique and powerful way. It is a commercial product which needs a subscription to run after a free evaluation period. To test the plugin just download it from the JetBrains marketplace. When it is started the first time it will automatically acquire an evaluation license that allows you to test the plugin for free for a period of two weeks. If you cannot access the Internet from IntelliJ you will need a file-based evaluation license. To do so you must register on www.hello2morrow.com and click on the red “Try Now” button.

If you want to continue using it after that you can buy a subscription (under 100 USD per year) from our website www.hello2morrow.com. Otherwise just uninstall the plugin. The different license options are described in more detail later in this article.

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How to Break a Big Ball of Mud?

Alexander von Zitzewitz Leave a comment

Many non-trivial systems end up as a big ball of mud, not because developers are lazy or reckless, but because it is very hard to avoid that outcome without proper tooling. For example, if your architecture rules are spread by word of mouth or some articles in your company wiki, there is no way of knowing if the code actually conforms to any of your architecture rules. If rules are broken, most of the times developers are not aware of that. That will lead to the erosion of architectural boundaries (if they ever existed) and more and more cyclic dependency groups. In the beginning the cyclic groups start small, but they grow like cancer in your codebase. I actually did some research on that by tracking some open source projects over time. That research confirmed my assumption – if you do not address the problem of ever growing cyclic dependency groups things will only get worse over time, in some cases much worse.

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Spring Modulith & Sonargraph – Better Together

Alexander von Zitzewitz Leave a comment

We created Sonargraph with the vision in mind, that it would allow architects to formally specify an enforceable architectural model. Another goal was to provide exceptional dependency visualization capabilities, so that issues could be easily detected not only in a formal way, but also by just looking at a dependency graph. Sonargraph’s architecture DSL (domain specific language) solved the first problem, while our exploration view solved the second one in a very unique and scalable way. The DSL is quite powerful and easy to learn. For an introduction you could read “How to Organize your Code” on this very site.

But obviously we were not the only ones thinking about a way to formally define architectural rules. Spring Modulith turned out to be a very powerful and successful solution to define domain driven architectures for Spring-Boot applications. Spring Modulith follows a pretty simple hands-off approach that allows the checking of architectural boundaries with a minimum configuration approach.

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Designing a Metric to Detect Big Balls of Mud

Alexander von Zitzewitz Leave a comment

Almost everyone who worked in software development for a while has come in contact with the dreaded big ball of mud (BBoM). If you are not familiar with the term, it describes software systems that have lost their architectural cohesion and suffer from extreme coupling and large cyclic dependency groups. That makes it much harder to do any changes on those systems, because everything is literally connected to everything else. Therefor it requires developers spending almost all their time trying to understand code before they can risk doing changes. And even then, the chance of regression bugs stay pretty high. If a system reaches this state, doing changes becomes so expensive, that rewriting the system from scratch might be cheaper than maintaining the old system. Unfortunately, very often it is not possible to rewrite the system, because the users can’t wait for years for a system replacement. This puts many development organization in a very uncomfortable place.

A big ball of mud visualized by Sonargraph

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Changes to the Sonargraph Dashboard

Alexander von Zitzewitz Leave a comment

The Sonargraph dashboard was designed to give the user a quick overview about several important aspects of software quality. The most important aspects in our opinion are “Architecture” and “Structure”, which are displayed at the top of the dashboard. After some internal discussions we decided that we could improve the metrics in the “Structure” box. Those changes will be rolled out with Sonargraph version 15.2.0, which is expected to be released this week.

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Using Sonargraph-Enterprise to Track Key Quality Metrics

Alexander von Zitzewitz Leave a comment

Sonargraph-Enterprise is designed to allow stake-holders to track important software quality metrics over time. The idea is that this would enable the early detection of harmful trends so that issues can be fixed while they are still easy to fix. The metrics displayed by Sonargraph-Enterprise can be fully customized by the user. However, in this article I will explain the “default” profile that comes with a set of preselected metrics that cover important aspects of code health and quality.

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