Write tests. Most likely those 300k lines of code contain a TESST folder with 4 unit tests written by an intern who retired to become a bonsai farmer in the 1990s, and none of them pass anymore. Things become much less stressful if you have something basic telling you you're still good.

I recommend reading a classic, "Working Effectively With Legacy Code" from Michael Feathers.

While great in theory, I think it almost always fails on "non-existent" testing structures that reliably cover the areas you're modifying. I change something, and if there's no immediate build or compile error, this (depending on the system) usually does not mean you're safe. A lot of issues happen on the interfaces (data in/out of the system) and certain advanced states and context. I wouldn't know how Mikado helps here.

In other words, I'd reword this to using the Mikado method to understand large codebases, or get a first glimpse of how things are connected and wired up. But to say it allows for _safe_ changes is stretching it a bit much.

Using a Mikado style graph for planning any large work in general has been really useful to me. Used it a lot at both Telia back in 2019 and Mentimeter at 2022.

It gives a great way to visualise the work needed to achieve a goal, without ever mentioning time.

I’ve been using a form of the Mikado Method based on a specific ordering of git commits (by message prefix) along with some pre commit hook scripts, governed by a document: https://docs.eblu.me/how-to/agent-change-process

I have this configured to feed in to an agent for large changes. It’s been working pretty well, still not perfect though… the tricky part is that it is very tempting (and maybe even sometimes correct) to not fully reset between mikado “iterations”, but then you wind up with a messy state transfer. The advantage so far has been that it’s easy to make progress while ditching a session context “poisoned” by some failure.

There is a great interview that talks about the process and what it is about more generally: https://youtu.be/HbjWOvxJjms?si=5ta-JOyfFLub2yX_

I think there are similar methods, such as nested todo-lists. But DAGs are exceptionally good for this use case of visualising work (Mikado graphs are DAGs).

1. take a well known method for problem solving basically any programmer/human knows 2. slap a cool word from the land of the rising sun 3.??? 4. profit! This article is painfully pretentious and stealth marketing for a book

So you do things one step at a time and timebox as you go? This method probably doesn't need its own name. In fact I think that's just what timeboxing is.

Inherited? I wrote the thing! Customer have no money for large refactoring.

In 2026, we call this "plan mode"

> The project doesn’t compile anymore.

Using a programming language that has a compiler, lucky.