The Elephant in the Room: Dealing with Legacy Code

As software developers, we've all been there. We inherit a codebase that's been around for years, with code files that are still in production but no longer meet our team's engineering standards. This legacy code can be a major headache, making it difficult to maintain, modify, and extend the system.

It’s easy to think of legacy code as something ancient and untouchable, written by long-gone developers in a forgotten dialect of JavaScript. But the truth is more complicated. Legacy code is just code that’s still running your systems, even though it no longer meets your team's standards. It might be hard to test. It might not follow your current patterns. It might still use the name of a product you rebranded three years ago.

So what do you do with it?

Legacy systems have a long memory... just like an elephant.

The First Rule: Don’t Panic

If legacy code is still in production, that means it’s still doing its job. Step one is to recognize that this code, flawed as it may be, is delivering value. That’s more than can be said for the code sitting half-finished on your local machine.

There’s a temptation to fix everything all at once. But rewriting legacy systems from scratch is a risky business. Just ask anyone who’s survived a failed rewrite. A better strategy is to improve what you have, piece by piece.

Start With the Why

Before you touch a single line of legacy code, ask this: Why does this code need to change?

Is it a security risk? Slowing down development? Making it hard to onboard new engineers? You need a reason more compelling than “it’s ugly.” Once you know why a change is needed, you can plan for how and when.

Make the Code Safer Before You Change It

One of the smartest things you can do before refactoring legacy code is to add tests around the areas you plan to touch. This might sound counterintuitive, especially if the code doesn’t have good test coverage to begin with. But establishing a basic safety net—even a few simple integration or smoke tests—can make a huge difference.

Michael Feathers, in his book Working Effectively with Legacy Code, defines legacy code as code without tests. His advice is to make code testable before making other changes. The goal isn’t to achieve perfect test coverage overnight, but to create guardrails that help you spot unexpected breakage.

Think of these tests like a seatbelt. You hope you won’t need them, but you’ll be glad they’re there when something goes wrong.

Go Small, Go Slow

Treat legacy code like a museum artifact. You wouldn’t clean an ancient vase with a power washer. Instead, change it carefully, in small steps, with a clear rollback plan. One great technique is what Martin Fowler calls the strangler fig pattern: gradually replacing parts of the system with new code, while the old code continues to do its job.

Bring in the Robots

One of the most effective ways to improve legacy code is to layer in modern tools that help you spot problems early and fix them automatically. These tools don’t need perfect code to start being helpful. In fact, they shine in messy, inconsistent projects.

Start by adding a linter like ESLint for JavaScript or ruff for Python. These tools help enforce consistent style and catch potential bugs. A formatter like Black can clean up code without changing what it does. And isort is great for keeping Python imports tidy and predictable.

Even better, make these tools part of your CI pipeline. That way, every commit gets a quick health check. You’ll start nudging legacy files in the right direction, one small change at a time.

If you're worried about overwhelming your team with a flood of linting errors, most of these tools let you run in “warn-only” mode. You can also start by targeting just a few directories or file types. The goal is progress, not perfection.

Automate the Repetitive Stuff

This is also a great time to introduce automation. If you find yourself fixing the same kind of thing over and over again—updating function names, rewriting config files, fixing linter errors—consider using tools like Codemod, or delegate it entirely to Caparra’s AI-powered tools. Let the bots handle the boring stuff.

Document What You Learn

As you work with legacy code, you’ll probably discover odd behaviors, hidden dependencies, and bits of tribal knowledge that never made it into the README. Capture that! Update the docs. Add comments. Drop notes into Slack.

This kind of documentation is a gift to your future self, and to every engineer who joins the team after you.

Know When to Walk Away

Not all legacy code deserves to be saved. If the system no longer serves a business need, or if maintaining it is more expensive than replacing it, it might be time to sunset the service entirely.

But when you do, do it gracefully. Communicate clearly. Give users time to adapt. Archive the code. And maybe raise a toast to the team that built it in the first place.

At Caparra, we believe that engineering teams do their best work when they have the mental space to focus on the high-value stuff. Legacy code can be a distraction, but it doesn’t have to be a nightmare. With the right approach, it can become an opportunity to improve your systems, level up your team, and build a codebase you’re proud to hand off.

Want help handling legacy systems, repetitive DevOps tasks, and other time-sinks? Open a free Caparra account. Our AI-powered tools are built to make DevOps easier to manage, even when you're dealing with a mountain of old code. Start building with Caparra today.