Documenting the Big Picture

In software development, it’s easy to focus on features and functionality as they’re the visible outcomes of your hard work. Yet, the unseen backbone of any project lies in its architecture and the decisions shaping it. Documenting architectural decisions is more than just record-keeping; it’s a strategic practice that lets developers manage complexity, make better choices, and maintain consistency. Sounds great – what do you need to know to get started?

Documenting the “why” of your code

When it comes to documenting your code, you've likely heard, "document the 'why,' not the 'what'." But effective documentation goes beyond the "why" of individual lines or methods; it’s also about the "why" at a structural level.

The big picture

Think of the next developer (many times being your future self) who’ll dive into your code months or years from now. They won’t just need to understand what a specific method does – they’ll need to grasp how all the components in your application interact and fit together. Your architecture is like a blueprint; without documentation, this big picture can easily become a mystery.

What should you include? First and foremost, outline the major components of your software and how they connect. For example:

• What architectural patterns have you used (for example, microservices, monolith, event-driven)?
• Are there any trade-offs or rejected ideas worth noting?
• Are there specific diagrams (like flowcharts or sequence diagrams) that could help someone new quickly see the big picture?

The value of big-picture documentation often becomes clear when you revisit old code. Think about a time you encountered your own past code and couldn’t remember why you made certain design choices. By capturing this overarching design context early on, you’re making life easier for future you as well as any teammates who may need to pick up where you left off.

Learning from the best

A great documentation resource to start with is in the Linux kernel commit message guidelines, which explain why commit messages (as just one form of documentation) are so important. This resource offers some great hints on how to talk about architectural and software changes, like describing the problem, describing the user-visible impact, and quantifying optimizations and trade-offs. It also covers best practices for referencing email threads, discussions, or external resources, something that’s often beneficial for providing context.

Another excellent resource is the C4 model, which aims to raise the maturity of software architecture diagrams by addressing four individual and ubiquitous levels of scope: (System) context, containers, components, and code. The C4 website provides many examples of how these different levels in a software system can be represented in a clear and concise way.

There’s also arc42, which offers a standardized template for software architecture communication and documentation. Providing consistent templates for multiple different tools and formats, arc42 helps developers explain all types of architectural information and decisions in an understandable and easily maintained way.

Close to the code

To prevent architectural documentation from going stale as your code evolves, keep it as close to the code as possible. This means storing high-level docs in the same repository, either within the source files or as a separate markdown file. (Whichever approach you choose, tools like PlantUML makes it easy to include UML diagrams directly into text.) Keeping documentation near the source provides a persistent reminder to update it during major changes. It also helps ensure that big-picture context is always handily nearby when developers need it.

Documentation starts at the top

Effective architectural documentation is an art that improves with practice. While detailed inline comments are great for explaining tricky parts of the code, don’t forget to document the overall design choices at the start of a new project, module, feature, or significant bug fix. This will give anyone looking at your code a map to understand your design thinking. Even a simple README or architecture.md file can be a helpful starting point.

Architectural documentation is more than just a formality – it’s a cornerstone of maintainable and scalable systems. By capturing the reasoning behind design decisions and hidden trade-offs, you create a roadmap that helps teams adapt to inevitable change. Whether you’re starting a new project or refining an existing one, investing in clear, thoughtful documentation ensures your architecture evolves with purpose. For more insights on building robust software, explore our series on development best practices.