Clean code is the key to software that will remain maintainable and efficient tomorrow. It reduces technical debt, speeds up development, and prevents your project from becoming an unmaintainable legacy monster. In this guide, you will learn how to pragmatically apply principles such as KISS and DRY to minimize errors and improve processes in the long term.
The most important information in brief
- What is clean code? Clean code refers to software code that is intuitive to understand, easy to read, and easy to maintain. It clearly communicates its intent and avoids unnecessary complexity, minimizing errors and speeding up adjustments.
- Why is clean code important? Clean code ensures that development teams remain capable of acting in the long term. It reduces time to market, shortens the training period for new developers, and prevents technical debt from blocking further development.
- What are the key principles? The most important guidelines are KISS (Keep It Simple, Stupid) for simplicity, DRY (Don't Repeat Yourself) to avoid duplication, and SRP (Single Responsibility Principle), according to which each component should only perform a single task.
- How do you implement clean code? Through continuous refactoring, disciplined code reviews (four-eyes principle), and test-driven development (TDD). Unclean code should be managed as technical debt in a backlog and systematically reduced.
Clean code – the advantages
- Rapid adaptability and efficient maintenance: Clean code significantly reduces the time to value. However, ignoring it can lead to a complete standstill in development in the long term.
- Comprehensibility and good testability: Clean code ensures stable software with fewer errors due to misunderstandings. In addition, well-tested code is more likely to better meet stakeholder requirements.
- Shorter onboarding time: New developers can find their way around the code more quickly, which shortens the training period and reduces dependence on a select few experts.
- Simpler replacement process: At the end of its life cycle, the code can be replaced more easily because tasks and side effects are clearly identifiable, reducing the potential for errors.
- Increased developer satisfaction: Clean code improves the quality of work and increases developer satisfaction, while messy code often causes frustration.
Clean code focuses on what matters: delivering value. It ensures fast, error-free and smooth development, while poor code constantly creates unexpected obstacles and destroys predictability. Clean code is therefore not just aesthetic, it enables teams to function in the first place.
Clean code development – a closer look
The everyday work of a developer involves, among other things...
- implementing new features,
- reviewing colleagues' code and
- fixing bugs.
To do this, the relevant piece of code must not only be found, but also understood – a real challenge if the code was written by another developer or has not been touched for a long time.
This is exactly where clean code comes into play: clean code should be easy to change and easy to read, thus making the daily work of developers easier.
Find out more about software modernization, including clean code, now.
KISS, DRY, SRP – Clean code principles at a glance
Clean code principles are guidelines that, when followed, can lead to clean, efficient, and maintainable code. These principles serve as guidelines and do not replace the developer's experience.
Preferred readability
If there are several possible solutions, always choose the one that is easiest for third parties to understand. Consistently replace cryptic variable names (e.g., "ints") with descriptive names (e.g., "ElapsedTimeInMilis"). This immediately increases clarity and speeds up subsequent maintenance work.
Keep It Simple, Stupid (KISS)
The same applies when writing code: Keep it simple. This means that you should constantly ask yourself whether the solution you have chosen is really the simplest one. This way, you avoid unnecessary complexity and end up with lean, understandable code. So: remember KISS and focus on the essentials without getting lost in details. This makes maintenance easier for everyone.
Don't Repeat Yourself (DRY)
Duplication must be avoided at all costs so that the same code does not have to be rewritten over and over again. This saves development time and means that errors only have to be fixed once.
Good to know: DRY (Don't Repeat Yourself) always requires careful consideration on the part of the developer. This is because two pieces of code that look the same are not necessarily duplicates if they can develop differently.
Single Responsibility Principle (SRP)
Each code unit should only perform a single, clearly defined task. Consistently separate mixed responsibilities: for example, a class should not manage orders and print invoices. Split these into separate units (order and invoice printer) to maximize testability and clarity.
Single Level of Abstraction (SLA)
Another principle of clean code is the ‘single level of abstraction’ principle. It states that the content of a function should always be at a single level of abstraction.
To illustrate this, let's imagine that the driver of a car is replaced by the function ‘DriveTo’. This function now controls the car – including the brakes, accelerator and steering wheel. However, it should not deal with more complex processes such as fuel supply and ignition. According to the SLA principle, these tasks belong to a different level of abstraction. This makes the code easier to read and understand.
Good to know: A reference to different abstraction levels can be the grouping of lines of code by comments or blank lines. These visual blocks often indicate that the operations belong to a separate abstraction level. Outsourcing these blocks to separate functions can improve the readability and structure of the code.
Composition on inheritance
Inheritance often leads to close coupling between classes, which makes changes difficult and encourages side effects. Instead, use composition: connect independent classes via clearly defined interfaces. This keeps the code modular, flexible, and much easier to test.
Good to know: One indication of poor code is when a parent class makes decisions based on the type or a property of the child class.
Be consistent
Treat as many aspects as possible in a consistent manner! This applies to the language used in the code, code conventions, and solution patterns for recurring problems. Consistency in the code increases comprehensibility and reduces the training time for new developers.
We identify weaknesses, provide clear recommendations, and support you in implementing clean code.
Proven practices for clean coding
In addition to clean code principles, there are also best practices that help developers write clean code. Here are some of the most important methods:
- Boy Scout Rule: Always leave the code cleaner than you found it. Small, continuous improvements (e.g., renaming variables, extracting methods) prevent creeping quality deterioration ("Broken Windows Theory") without much extra effort.
- Root cause analysis: Don't just fix the symptoms, fix the root cause of the problem. Superficial fixes increase the complexity and error-prone nature of the software in the long term. Invest the time to understand why an error occurred.
- Iteration, reflection, and the dual control principle: Clean coding is a continuous process. Consider unclean code as technical debt, manage it in a technical debt backlog, and schedule fixed times for its reduction. In addition, early reflection ensures quality: use code reviews or pair programming to get feedback directly during implementation. Formats such as a "tech weekly" also promote knowledge exchange within the team.
- Test Driven Development (TDD): Write the test before the actual code. This enforces clear, decoupled interfaces from the outset, as the test acts as the first "user" of the code. TDD guarantees technical correctness and creates a safety net for future refactoring.
Clean code development – challenges during implementation
Every challenge can be overcome. Let's take a look at the potential challenges you may face during implementation:
Wrong priorities (features vs. quality): Often, too much focus is placed on new features, while code quality is neglected. The result: technical debt increases and development speed decreases.
- Solution: Use the technical debt backlog mentioned above to plan debt reduction as an integral part of the sprint.
Unclear requirements: When requirements are vague, the complexity of the solution often does not match the problem, or domain terms are incorrectly named in the code.
- Solution: Clarify terms and logic before writing the first line of code. Incorrect naming is difficult to correct later on.
Lack of discipline & legacy code: Clean code is never "finished." It requires daily discipline on the part of everyone involved to adhere to the principles. This is particularly difficult with legacy code (existing projects), as a deep understanding of the old structures is necessary before tidying up can begin.
- Solution: Establish fixed routines such as code reviews (four-eyes principle) and pair programming. When dealing with legacy code, consistently apply the Boy Scout Rule: improve the code step by step with each change, instead of trying to rewrite everything at once.
Clean Code – tidy up your code
Clean code is more than just aesthetics—it is the foundation for software that remains maintainable and extensible in the long term. Those who skimp on code quality today will pay for it tomorrow with interest and compound interest in the form of technical debt.
We support you in this process: Whether it's refactoring legacy code, introducing TDD, or conducting targeted code audits, our experts help your team pragmatically embed the principles of clean code into their daily work. Make your software future-proof.
FAQs on clean code
Is clean code worthwhile even when time is of the essence?
Yes. In the short term, “quick and dirty” may save time, but in the medium to long term, poor code slows down development significantly (“technical debt”). Clean code ensures that development speed (velocity) remains consistently high.How do I get started with existing “legacy code”?
Apply the Boy Scout Rule: Don't try to rewrite the entire system at once. Instead, improve the affected section of code minimally with each bug fix or new feature. This will increase quality iteratively.
How does clean code relate to agile development?
Clean code supports agile methods through short feedback cycles and the ability to respond quickly to changes, resulting in more efficient development.
Is clean code only relevant for large projects?
No. Small projects also benefit from clear naming and structure (KISS principle). Since small projects often grow, clean code lays the foundation for them to remain scalable later on without having to be completely rewritten.
Richard Gross is Head of Software Archaeology and has been working in IT modernisation since 2013. As a member of the division management team, he drives forward topics such as technical excellence. As a team leader and architect, he supports teams in achieving a return on investment as early and continuously as possible. To achieve this, he coaches teams in code quality, test automation and collective ownership. His technical focus is on hexagonal architectures, test DSLs, hypermedia APIs and the expressive and unambiguous modelling of the domain as code. Richard shares his knowledge through active pair programming, training courses, technical articles and presentations at international conferences. He has also been involved for many years in the open source project CodeCharta, which enables non-developers to gain an understanding of the quality of their software.