IT systems

Legacy code - what is legacy code?

Graphic shows a person trying to fix the system depicted on a large monitor screen

The words "legacy code" can induce goosebumps in many a programmer. Legacy code, in many cases, means having to wade through layers of complex and complicated notation with the hope that subsequent changes will not bring harm to the software being developed. Legacy code, however, should not only worry programmers. Many companies will find code that has become difficult and expensive to maintain through years of overwriting. Such code is not only tedious and time-consuming work for your team, but also risks significantly slowing down software development. What is Legacy Code, how can it affect our company's development and how do we deal with it? It turns out that legacy code doesn't have to be as scary as they paint it.

What is the Legacy Code?

Legacy code is somewhat reminiscent of some of the iconic characters played by Sylvester Stallone - life-weary veterans who, despite their many experiences, still try to rise to the occasion, but as they get older and "fight battles" become more difficult. Legacy code, like Rocky Balboa, for example, was once at the height of its fame - fully functional, efficient and reliable. With the passage of time, more struggles, challenges and "injuries," it began to lose its efficiency, and keeping it in shape became demanding and problematic. This is more or less what Legacy Code looks like - that is, source code that was written a long time ago, but over the years - due to successive changes and modifications - has become difficult to understand and maintain.

We most often deal with legacy code in the case of projects developed over a long period of time. The initial assumptions change, individual specialists or even entire teams working on the application are replaced, and sometimes the project implementation is handed over to an external company. Very rarely can we afford the luxury of starting the entire project from scratch, so new programmers have to contend with extensive code that has undergone successive transformations - gaining new features or carelessly patched bugs in it. Legacy code as a result is unreadable code, while the lack of carefully maintained documentation and regular refactoring makes it difficult and time-consuming to work with. What's more, the more "aged" source code you have in a project, the greater the chance that it is already outdated - it was created when completely different programming standards were in effect, which means it may not meet many quality requirements today. But is Legacy code a problem that can't be solved?

How does legacy code affect software development? 

Neglected and devoid of careful optimization, legacy code will not only increase the risk of bugs in the application itself, but will begin to have an increasing impact on subsequent aspects of the entire project - including its cost, quality, performance, as well as its execution time. Legacy code, left without proper attention and work, will consistently increase our company's technology debt, slow down software development and even the entire organization. Meanwhile, in extreme cases, it can pose a threat to the security of our system and data.

However, the situation is not as bad as it might seem. There are ways and practices that will allow us to minimize or even reduce to zero the problems and risks associated with the existence of Legacy Code in our company. It is also worth remembering that any code created that is not taken care of in the right way will eventually get old. Therefore, it is important to think about certain measures now and start implementing them consistently.

How to deal with legacy code? 

Working with legacy code can be a challenge for our developers - it requires caution, careful planning and, above all, patience. All this is done to minimize its negative impact on software development and avoid generating accumulating errors. However, taking certain measures can help us deal with legacy code. Refactoring the code will significantly improve its quality, while keeping careful documentation will significantly prolong its readability and make it easier for developers joining the project. There are several actions that will make it easier for us to work with legacy code.

  • Take the time to analyze the code - taking a close look at legacy code and understanding what functions its various elements perform is the first step to taming Legacy Code. However, we must be aware that we will not analyze all the code in one day. However, if our specialists take a little more time to understand each piece of code, they will make their work much easier, and the subsequent optimization of the code will become much simpler.
  • Familiarize yourself with the documentation - working on Legacy Code is one of those situations where having carefully maintained documentation will be appreciated. Having access to the project's documentation will allow us to familiarize ourselves with the project's initial design, which will be an invaluable aid in understanding the changes that have been made to the code over the years. This will certainly increase the productivity of our developers. At the same time, working on Legacy Code will be a great opportunity to update the current documentation.
  • Frequent testing of code - testing is an extremely important part of working with Legacy Code. The introduction of major changes to code fragments should always be followed by thorough testing. Only in this way will we be able to increase our control over the operation of the system after the changes. 
  • Code refactoring - the most effective action in struggling with legacy code will be to subject it to a refactoring process. This process involves improving, transforming and simplifying the current code to make it more readable. In short, it's cleaning up the clutter that has built up over the years in the code, making it easier to use and more understandable for current and future developers who will be working on it.

Code refactoring - what is it?

As we mentioned above, one of the basic and most effective actions we can take when working with complex legacy code - is code refactoring. This process involves restructuring the existing source code, without interfering with its functionality. The purpose of such a procedure is primarily to improve the overall quality of the code, increase its readability and bring it into a form that is easier to maintain. As part of refactoring, we can, among other things, change the naming, remove unnecessary code fragments, improve its formatting, and split long functions into much smaller ones. After such a procedure, fixing bugs or adding new functionality will become much simpler, which will translate, among other things, into team productivity and reduce the time needed to deliver the product.

When and why should you refactor your code?

We should be constantly concerned about the quality of the code we have. Therefore, the best solution is to regularly perform refactoring as part of the development cycle along with the development of the application or system itself. This will be the most effective way to avoid problems arising from having extensive code. It is possible that due to tight deadlines, numerous changes during the project or dynamic development of the solution we have already neglected our code. What signals will tell us that it is high time to perform refactoring? 

There are several signs that it is high time to refactor legacy code:

  • Information from programmers - no one likes to work hard, and wading through layers of unstructured and complex code is frustrating. Therefore, it is probably the programmers themselves who will be the first to let us know that the code they are working on needs refactoring. 
  • Increasing number of errors - another worrying sign of the need to clean up the code is the increasing number of errors that appear. If the increased number of errors is accompanied by slowing down of the application and difficulties in implementing new functionality, it is a sign that it is high time to refactor the code. 
  • Use of obsolete technologies - the world of new technologies is changing very fast, and if your system is already years old, it was certainly developed using already obsolete technologies and according to outdated standards. Refactoring in such a case will work like a rejuvenation treatment.
  • Scalability problems - numerous bugs, problematic implementations of functionality and prolonged work on even simple elements will make our solution unable to meet the ever-changing needs of our users, and we cannot afford this.
  • The cost of maintaining the system is starting to rise - one of the best arguments for refactoring the code, is the chance to significantly reduce the cost of the ongoing project.
  • Problems with further development of the system - the market and customer needs are constantly changing. The competition is not sleeping and is certainly investing in the development of their applications. It's high time to think about automating internal processes, but you are still working on the application? Legacy code can contribute to slowing down work on the system, and in turn, can translate into the development of the entire company. Performing code refactoring, not only saves money, but saves your developers' equally important time.

If you notice any, even the smallest signals indicating that you need to improve the quality of the code you have - do not delay refactoring. 

What are the benefits of code refactoring?

Refactoring is a process that will bring many benefits to our organization. The main one is a significant improvement in the quality and readability of the code, which will quickly translate into efficiency for our programmers. Clean code will speed up work, minimize the number of errors that occur during the development process and make it easier to expand the application with new functionalities. Taking care of code transparency will also have a long-term significance - in this way we will make it easier to scale the application in the future and later develop the project. An additional benefit of performing code refactoring is to increase the security of our system. All of the above, on the other hand, will mean savings - both in terms of time and costs associated with the development of the system, so we can avoid incurring a serious technological debt.

Code subjected to regular refactoring is the basis for building high-quality digital products. If we want an application or a website to realize its objectives and fully meet the needs of users, and its development does not involve tedious work - let's take care of the quality of the code, both during the project and immediately after its completion.

How do refactoring tools work?

We can carry out the process of code refactoring with the help of appropriate tools. Refactoring software will help our programmers automate and speed up the whole process. They analyze our source code and then show us where we can make changes. In addition, they detect and remove redundant or duplicate lines of code, organize its structure, increase readability or improve coding style. Code refactoring tools can also check the behavior of code and point out errors even before it is run. With access to code refactoring programs, our programmers can focus on completing more creative tasks. It is worth remembering, however, that refactoring tools themselves are first and foremost a support for programmers, and it should not be assumed that the work done by the tool, will not require subsequent verification.

Using such tools will increase the productivity of our developers, make the process of improving code quality easier for us, as well as save time and reduce project costs.

Is it possible to deal with legacy code without refactoring?

Of course we can deal with inherited code without refactoring. The question, however, is whether this approach will be profitable for us both in the short and long term. Instead of refactoring, we can bet on conducting extensive rewrites, which can help us prevent regressions when implementing new functionality. Another strategy will be to gradually replace some of the code we have with new code. However, both of these solutions will consume valuable time and involve our specialists. 

Refactoring is very often the most effective and cost-efficient way to solve the problems caused by having outdated code.


Legacy code can be compared to veterans who lose their prowess over time. It is old source code that becomes difficult to understand and maintain over the years. It negatively affects software development, costs and system security. Refactoring code is a key part of transforming it, improving quality and readability. Refactoring tools help streamline this process. The choice between refactoring and other strategies depends on our priorities, but it is often the most cost-effective option in the long run.