Refactoring Legacy Code: Steps and Best Practices

Legacy Code Refactoring

As your company or product grows, chances are your code has passed through several developers, and the code base is no longer neatly structured but continually patched. Having a software application that freezes, crashes, and behaves abnormally is a company’s worst nightmare.

Apart from staining your brand’s reputation, this can limit your company’s ability to scale. A decade-old generic software with crufty legacy code messes with the functionality of your software application, creating technical debt and stunting your company’s growth or worse, normal functionality.

So, what do you do when you find yourself with a clunky, outdated, and messy code, which is harder to reuse and test?

There are two options, you can either rewrite the entire code or refactor it. On one hand, rewriting is quite easy for the developers but comes at a hefty price. And on the other, you can save costs through refactoring the code, which is significantly cheaper but very difficult. The good news is that it’s possible to fix it without the need to disrupt the entire company’s internal and external processes. In this short and to-the-point article, we are going to walk you through the process of legacy code refactoring, revealing the common pitfalls and how you can dodge them.

So, What is Refactoring Legacy Code?

Refactoring legacy code is the process of improving the structure of an old or unfamiliar code without changing its functionality. The idea is to clean up lines of complex codes so you can understand or work with them better. This may include reducing redundancies or errors to make the code readable and manageable.

While refactoring a legacy code may sound similar to rewriting it, they differ.

In a code rewrite, developers would remove nearly everything to create a new code and implement new functionality from scratch. Refactoring is less extreme. Think of it like editing your old high school paper. When you review it, chances are you may find wordy sentences or repetitions that serve little use to the essay. When you improve these words without altering the meaning, that’s refactoring for programmers.

Legacy code refactoring scheme

Legacy code refactoring works on the basic principle of cleaning up the code base to improve its performance, making it readable and easy to maintain.

There are various benefits to careful refactoring legacy code. For starters:

  • It makes code easy to understand: Refactoring code involves restructuring code in such a way that a new developer can work on it with minimal difficulties. When it’s understandable, identifying and fixing bugs becomes effortless.
  • It enhances maintainability: Organized code is easy to maintain and improve. It also makes updating the code pretty much straightforward.
  • It improves an application’s performance: With less complex codes, a software application functions faster.
  • It is cost-effective: In the long run, simplified and restructured code will be efficient. It also minimizes the risk of bugs, which is time and cost-saving.

It provides technical support: Technical support allows you to use third-party APIs that improve the functionality of your enterprise application. You will also receive updates that fix bugs and repair existing security holes.

Legacy Code Refactoring vs. Code Rewriting: What to Choose

Rewriting is another solution to dealing with unmanageable codes. As opposed to testing and refactoring legacy code where a developer makes micro changes to an application, code rewriting (as the name suggests) is scraping away the code and building it again from the ground up.

So, when can you rewrite the code?

Rewriting is a viable option if you want to switch the application’s architecture dramatically. It is also the case when the application’s tech is turning obsolete, only supports previous versions of the system, and cannot integrate with advanced applications.

Take the example of AngularJS.

It was not long ago when Google discontinued support for AngularJS. As a result, companies that use the programming language for their web applications will no longer receive updates and cannot leverage third-party APIs. In this case, considering migrating AngularJS to Angular is a necessary step.

Legacy code refactoring alone won’t work here. You do need to makeover the entire application and rewrite codes afresh due to differences in frameworks.

On the other hand, who should refactor legacy code?

If the application is an integral part of business processes and stopping it will cause too much downtime, refactoring it is an excellent idea. This also applies if the primary app developers are available and can work on the software.

Pros and cons of code rewriting

Rewriting code allows you to change code, improving it however you deem fit. It also does away with legacy code that can make system integrations near impossible.

Even so, rewriting is time-consuming. Developers need to take time to understand the application, identify the must-have functionalities, and devise ways to incorporate them into the new code. Additionally, the risk of developing new bugs and defects is high.

Pros and cons of code refactoring

One of the major advantages of refactoring in a legacy code is that it can be done to any software architecture. It also improves the quality of code without unnecessary downtime, and developers can choose to isolate a specific codebase and work on it independently, which significantly minimizes development costs.

However, since refactoring does not tamper with the functionality of the application, you cannot add new features. It also requires robust skillsets to simplify the code, as the process is often complex.

When should you refactor or rewrite legacy code?

All in all, before you decide on whether to rewrite the code from scratch or refactor it, you need to scrutinize each option, choosing the most valuable strategy in terms of complexity, cost-effectiveness, and time used in the development process.

Simple Steps to Refactor Legacy Code Base

Every developer has a methodology for refactoring legacy code that’s unique to them. However, all of them conform to a few basic steps when integrating legacy systems.

Here is a simple step-by-step guide on how to refactor legacy code.

The process of legacy code refactoring

Identify the flaws and flows

In many cases, legacy code has more than one flaw. And improving its internal structure starts with identifying the root problems.

For instance, if you are refactoring PHP legacy code and you are dealing with old-fashioned core functionalities, you first need to identify how well-documented, operational, and scalable the PHP application is.

Performing a comprehensive application audit is instrumental when working effectively with legacy code, as you gain viability into the faulty flows and their dependencies.

Break monolith code

Effectively refactoring code requires you to split each monolith code, separate them into focused classes, modify the code, test, and release the refactor thereafter.

Splitting code is an integral part of the refactoring process as it improves readability, helping the developer to focus on specific modules, and gain an in-depth understanding of the codebase. They will then be able to accurately picture their objective and articulate their next steps.

Extract logic code and apply the basic refactoring tips

The next phase of refactoring is to extract each flow’s set of principles necessary for the proper functioning of the application. Rewrite it, taking a more straightforward approach.

Write code bearing in mind the effective coding principles. Doing so makes the code highly scalable, allowing you to add a dependency if need be. However, first, you need to concentrate on the logic iteration you are working on before you can think of the dependencies. And then, test!

Undertake all these while staying true to the basic principles of legacy code refactoring is imperative. For starters, you need to refactor in small bits rather than in large batches. Also, instead of refactoring the entire UI only work on specific codes that affect the particular business request.

Choose your desired architecture

Choosing the right software architecture is of the utmost importance as it plays a vital role in how the application handles the functions it was designed for. It also determines the hurdles you might face during implementation.

Before picking the desired architecture, you need to consider component interactions, the application’s scalability, and adaptability. Some of the architectures you can pick from include layered, microservices, event-driven, and space-based architectures. If you are indecisive and having problems picking one, you can always mix multiple architectures.

Legacy Code Refactoring Best Practices

If you are wondering how to begin refactoring legacy code, you have come to the right place!

ModLogix is a legacy software modernization company. We conduct professional code quality audits and are well-known for our ability to refactor even the most complex enterprise applications.

So, what is the approach to refactor legacy code? Some of our refactoring best practices include:

Understanding code

The company culture at ModLogix calls for collaboration. As such, we work collaboratively with the team to ensure we understand the legacy code, its classes, and its components. We take an intricate look at the source code to understand the flows.

Refactoring for future success

ModLogix does not undertake refactoring as a one-time task but as a continuous process. With the ever-changing technologies, we understand that improving code regularly gives your business a competitive advantage.

Furthermore, we refactor bit by bit, working on one module at a time. To ensure a successful project, we will clean up the code before we can include any additional features that you deem necessary.

Testing often

ModLogix tests, tests, and tests! Doing so after every refactor allows us to identify alterations in the application’s functionality earlier on. It also helps us know if we have re-introduced any bugs or not.

Final Thoughts

Legacy code refactoring is an excellent option for businesses that want to clean up their legacy software, making it easy to understand. It also makes the application easy to manage and improves its scalability. It is also a viable solution for software applications coded with robust programming languages, including C# and Java, aiming to enhance efficiency in business processes, increase productivity, and give the company a competitive edge.

Originally published at on February 16, 2022.



ModLogix helps organizations move legacy applications to new secure, stable, and scalable platforms. To explore more, please visit

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ModLogix helps organizations move legacy applications to new secure, stable, and scalable platforms. To explore more, please visit