YAGNI Principle in Software Development: Do You Really Need That Abstraction or Generic Code?

What Is YAGNI? Don’t Build What You’re Not Gonna Need

At the core of this discussion is the YAGNI principle, which stands for You Aren’t Gonna Need It—a key concept from Extreme Programming and lean software development. As Derek explains, YAGNI tells developers not to implement features or functionality they think they'll need in the future, but rather to focus on current requirements.

Derek adds nuance: while you should avoid writing speculative code, you also don’t want to handcuff yourself from adapting later. The challenge is to avoid spending time on features that might be useful while still being open to change. This is a common dilemma in agile software and software engineering.

He describes two common misapplications of YAGNI:

1. Feature Planning – You anticipate future requirements and start building now.

2. Code Abstractions – You generalize or abstract existing code too early, guessing at other features that might be needed.

In both cases, the result is usually wasted effort, added complexity, and feature creep—the exact opposite of what good practice and the KISS principle (Keep It Simple, Stupid) promote.

A Real Example: Shipment Notification System

To illustrate, Derek uses the example of a shipment management system that sends an SMS to a user once their package is delivered. The system uses Twilio, and the feature works by handling a delivery event, fetching contact information, and sending a message.

This straightforward code development process addresses the current requirement. It’s simple, testable, and delivers value. But then, the question arises: What if we want to change SMS providers in the future?

This is where many developers invoke the YAGNI principle incorrectly. They assume that because another implementation might come later, they need to abstract the SMS logic now. So they create an interface like ISmsService.

Abstractions: Are You Building for a Future That May Not Exist?

Derek challenges this early abstraction: if you only have one implementation, and no current requirement to switch providers, then why abstract? You're adding unnecessary complexity to make life easier in a future need that may never materialize.

He goes further by illustrating the software engineering cost. When you eventually add a second provider, you realize your interface is too tightly coupled to Twilio’s specific needs (like its “from” phone number logic). Suddenly, the abstraction becomes a liability. This is how abstractions built on limited knowledge often introduce bugs and complicate refactoring.

The key takeaway here: you’re not saving time, you’re building something wrong due to insufficient context.

Going Generic Too Early: A Developer Trap

One of the most common YAGNI violations in computer science projects is the push to make things generic before they need to be. Derek explores this through another example—grouping SMS and email notifications into a single, generic notification system.

To do this, a developer might define a NotificationType (SMS or Email), a universal address field, and create a single service that handles both. But this overly abstract design ends up complicating logic and creating conditional code paths that are fragile and difficult to maintain.

This is classic feature creep and a hallmark of ignoring lean software development and solid principles. You’re writing speculative code that serves no immediate user need—a red flag in any agile software development process.

Prefer Extension Over Modification

Rather than over-engineering, Derek suggests a simplest solution approach: if you later need to support email notifications, just implement that feature separately.

Using an event-driven architecture, each event can trigger multiple independent handlers. For example, one handler for SMS and another for email. You can later remove one without affecting the other. This method promotes simplicity, supports changing requirements, and respects the separation of concerns—all of which align with agile and test driven development best practices.

By building systems that are extensible, not over-designed, you maintain flexibility without predicting every possible future. This is how you avoid unnecessary complexity and stay adaptable.

The Real Cost of Violating YAGNI

Derek highlights the real cost of building unnecessary features:

• Time spent building something you never use

• Added complexity that doesn’t provide immediate value

• Increased ownership cost for developers who now have to maintain unused or overbuilt code

• More room for bugs and errors due to overengineering

This aligns with another core principle of agile software development: focus on delivering value now, not possibly later.

He notes that experienced developers often make the mistake of trusting their instincts about future needs—and are wrong. Even with experience, predicting what your system will need months from now is often a losing game.

Final Thoughts: Context Matters, Simplicity Wins

Derek wraps up by clarifying that he isn’t against design principles or abstractions. In fact, he believes in building systems that can evolve. But the mistake is in implementing things without current justification—essentially violating YAGNI.

He encourages developers to “write code and implement features that have value now.” Avoid chasing future requirements at the expense of your current users. Stick to clean code practices and favor design strategies that support change without locking you into speculative structures.

He also invites developers to share their own YAGNI horror stories, where they built for the future and never needed it—a common tale in many projects.

Conclusion: Apply YAGNI to Your Development Process

The YAGNI principle remains one of the most valuable tools in a developer’s toolbox. It aligns with agile, lean, and KISS philosophies, reminding us to build only what is needed—nothing more. Derek Comartin’s breakdown of this idea in his video, through real-world code and development process examples, offers clear guidance on how to apply YAGNI effectively.

So the next time you’re tempted to add a layer of abstraction, a generic class, or an extra feature, pause and ask yourself:

Are you solving a problem you have—or one you’re only guessing might appear someday?

Avoid spending time on imaginary futures. Focus on building value today. Keep your software simple, maintainable, and responsive to real needs.

Because chances are—you aren’t gonna need it.