What is legacy code?
Introduction – why the topic of legacy code is important
In the world of software development, the term legacy code appears more often than one might think. It applies to both small companies and large corporations, regardless of the industry.Understanding what legacy code is helps avoid many problems, improves project planning, and aids in keeping applications in good condition. In practice, every developer or website owner may encounter it.
According to the definition proposed by Michael Feathers, author of the book Working Effectively with Legacy Code, legacy code is code without unit tests, although in everyday usage it simply means “old” or difficult-to-modify code.
Definition of legacy code
Legacy code literally means “inherited code.” It can be code written many years ago, but just as well code created only a few months ago if it is difficult to maintain.It is characterized by a lack of up-to-date documentation, insufficient test coverage, and often outdated technologies. The problem is not its mere existence, but the fact that any change may carry a high risk of introducing new bugs.
It’s worth remembering that legacy code is not always “bad” — sometimes it has worked correctly for years and requires no intervention until the need for new features or integrations arises.
Causes of legacy code
There are many reasons why legacy code appears in projects. One of the most common is the lack of long-term planning — code is created in haste to meet short-term business goals.Another factor is developer team turnover — new members inherit code from predecessors without always having full knowledge of its structure. Additionally, technologies change quickly, so solutions that were modern 5 years ago may be difficult to maintain today.
A frequent cause is also a lack of updates — systems run on old versions of frameworks, libraries, or programming languages, making integration with new tools more difficult.
Challenges of legacy code
Working with legacy code brings a number of challenges. One is the high cost of maintenance — fixes and changes take more time, and each modification requires additional testing.Another problem is the difficulty in adding new features — often many parts of the code need to be modified to implement what seems like a simple change. A lack of documentation further prolongs the process.
Legacy code can also be a source of frustration for development teams, as it requires great patience, and the results are less visible compared to creating new projects.
How to recognize legacy code
There are several signs that may indicate we are dealing with legacy code:1. No or outdated technical documentation
2. Low code readability and lack of consistent standards
3. Lack of unit and automated tests
4. Use of outdated technologies or libraries
5. Frequent bugs appearing after each change
In practice, it is worth conducting a code audit — an analysis that helps assess its quality, compliance with current standards, and scalability. Such audits are standard in professional software companies and help plan modernization strategies.
How to deal with legacy code
There are several ways to deal with legacy code. One is refactoring — gradually improving the code without changing its functionality. This helps increase readability and introduce tests step by step.Another method is rewriting modules from scratch — used when fixing existing code is less cost-effective than creating it anew. However, it’s important to remember that this is a costly and time-consuming option.
The best results come from a gradual modernization approach — combining refactoring with replacing selected elements, which minimizes the risk of system downtime. In this process, tools for automated testing, version control systems, and code quality analysis (e.g., SonarQube) are helpful.
Summary – is legacy code always a problem?
Legacy code is a natural phenomenon in the IT world. It is impossible to avoid it entirely, as technologies, business needs, and teams are constantly changing.The most important thing is the approach — treating legacy code as something that can be managed. Regular audits, testing, refactoring, and investing in documentation help keep projects in good condition.
Well-managed legacy code can continue to bring benefits to a company for many years, and its modernization can become an opportunity to improve the overall system quality and implement modern solutions.
Client Reviews
Selected Projects
Each project is a custom-tailored online store or web application that combines modern design with functionality adapted to the client's needs. See how we help brands grow in the online channel through thoughtful and comprehensive implementations.
Case study
PawsOfLily Online Store
Scope of Work For the PawsOfLily brand, we designed and developed a modern online store from scratch based on WordPress. The project included creating a tailored visual design, integrating with a payment system, inventory management, and shipping (InPost).We ensured that the entire platform was not only visually appealing but also intuitive and functional — in line with best practices for building websites and web applications. At the end, we conducted a training session that enabled the client to manage the store independently from day one. Technologies Used Read more
Case study
Mellowmind Cosplay Online Store
Scope of Work For the Mellowmind Cosplay brand, we designed and developed a modern online store from scratch based on WordPress. The project included preparing a unique, bold visual design that reflects the character and aesthetics of the brand, as well as full integration with the payment system.We ensured that the store was not only visually aligned with the brand's existing communication but also fully functional, scalable, and ready for future growth. At the end of the implementation, we conducted a training session that enabled the client to independently manage content and product offerings. Technologies Used Read more
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Soteria Web Application
Scope of Work For the Soteria project, we designed and developed a modern online store with a booking module, based on a custom system built in Laravel technology. Work began with preparing a tailored graphic design that visually referenced the brand's character and the interior aesthetics of the restaurant.Then we proceeded to implementation — creating a fully functional sales system with the possibility to make online reservations. The entire system was tested for usability, responsiveness, and stability in the production environment. Technologies Used Read more
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Silverpine Ridge Website
Scope of Work For the Silverpine Ridge project, we designed and implemented a website dedicated to presenting the offer of single-family homes for sale and rent. The starting point was a refined graphic design aimed at capturing the atmosphere of the place — a peaceful, modern estate surrounded by nature. Then we completed the full implementation of the site using Laravel technology and carried out final tests. Technologies Used Read more
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VICE Landing Page
Scope of Work The VICE website was created with a focus on modern aesthetics and clarity of information. The goal was to design a clean, functional WordPress site aligned with a minimalist visual identity. The result combines simplicity with a strong message — all developed in the spirit of 'less is more'. Technologies Used Read more