I've been in situations where I was sure this was true. I've also been in situations where the person claiming it simply refused to become competent in the language, framework, or persistence technology that the system was built on.

Also subjective: "The business needs a capability the current code was never shaped to grow into." Most of the times I've heard this brought up, it's not that you need a re-write, but you need a re-architecture. Often the existing system can continue to do its job as it always has, but in a new architectural context. Or 90% of the code can stay the same, while the application it runs in is changed, for example from a web service to a Kakfa consumer. (This is why it's so important to avoid languages and frameworks that are tightly bound to an architectural choice.)

> why it was worth doing, because it wasn't, at least not to the business. The application did the same job for the same users at the same speed as before.

Application have many other properties then "doing their job". Running cost, maintainability, ... it's endless. Any of them going seriously wrong can tank the company owning it.

But I agree, rewrites are very often bad. I've been the customer of two banks that spent years to rewrite their online bank. It was crap and missing features! But maybe they got something out of it.

Rewrites usually start with a gap in what is available and what is needed: missing functionality, existing frameworks getting obsolete, difficultly maintaining code because of the existing implementation complexity, costs, scalability issues, compliance challenges, etc. Most of these things serve the business more than the engineers.

you’ll only find out which kind of rewrite you’re doing once you start it.

Until one day our dear team lead rammed a full NodeJS rewrite down our throats.

Never just write code. Always write red tests first.

In fact you can do even better and have your agent write end-to-end tests first as acceptance tests, have it witness them fail, then have it do red/green at the unit/component/integration level. Once it’s done the e2e tests pass, have it send the code off for linting and self-review.

If you are vigilant you’ll end up with a trustworthy validation suite. And with that (especially with e2e coverage), you can refactor and rewrite as much as you like.

One big caveat to this is that a large (and increasing) part of the value of the senior engineering hire is their taste. ‘Taste’ as honed by the software industry approximates business needs that the business doesn't even know it has. Sometimes engineers struggle to articulate ‘why’ a particular change is beneficial because they're just pattern-matching: they've seen the existing pattern break in a dozen different ways in a dozen different codebases, so now when they see the same thing again it ‘offends their taste’ — it looks indefinably wrong even though it doesn't seem to be causing any direct harm right now.

(Of course, sometimes it turns out just to be that they don't understand what's going on, especially but not exclusively for more junior engineers. Pobody's nerfect.)

Title is somewhat clickbaity, because these actions are not what people are going to think of when they think of a rewrite in a corporate environment.

By the way, I was an early employee at Amazon.com and the website’s rendering engine was rewritten three times, each time unlocking a new level of productivity without which the site (as well as the velocity of teams) would have slowed to a crawl, and the company would have probably died.

In ML e.g., there is the concept of a "ceiling analysis". I don't see why a variant of this wouldn't work here too.

The article is also wrong. Or, at least, indicative of a broken relationship between management and engineering. If you have an engineer who can decide to rewrite the entire product without management buy-in, then that's an organisational and a discipline problem.

Added to which, of course, maintainability and build-ability both matter an enormous amount. Work to improve both of those things will improve the business.

I always do that. I used to assume they knew better than I. I've been wrong a lot about that.

Except the Rust rewrites that have been ordered directly by "business"

Part of Yahoo's business is/was hiring programmers reasonably cheaply and controlling them reasonably easily - to allow Yahoo itself to sell parts or all of itself.

So things aren't quite a simple as "this doesn't serve the product", sometimes the engineers (and their replaceability) are part of the product.

I mean, if you do it at 4am, you are sleep deprived by the day two and thus unable to stop yourself from something stupid.