Case Studies: C4 in Small-Scale Projects
One of the most common sources of wasted time in early software design is treating architecture as a one-off documentation task rather than an evolving conversation. Teams often spend hours drawing complex diagrams that no one reviews, understand, or update. The real shift isn’t about tools—it’s about recognizing that C4 model case studies aren’t just for large systems. They’re powerful in small projects too. When you start with a simple system context diagram—even for a basic to-do app—you’re not over-engineering. You’re establishing clarity from day one. This chapter shows how applying the C4 model to small project C4 diagrams prevents future rework and improves team alignment.
I’ve seen teams rebuild entire mobile apps because no one had documented how components interacted. A single miscommunication led to duplicated logic and a tangled codebase. The fix? Not rewriting, but starting with a Level 1 C4 diagram. You’ll learn how even modest systems benefit from structured abstraction, and how C4 model real world examples demonstrate that simplicity isn’t a limitation—it’s a strength.
Why Small Projects Need C4 Too
It’s tempting to think C4 only applies to enterprise systems. But the truth is, small projects suffer from the same architectural drift—just faster.
Without any formal structure, developers make assumptions. One team built a fitness tracking app using a single monolithic backend. Two months in, they added a new feature: real-time syncing. Without a component diagram, they didn’t realize the notification service was tightly coupled to the workout processor. The fix required a full refactor, costing weeks of effort.
Now, imagine if they’d started with a Level 2 C4 diagram. They would’ve seen the container boundaries and dependencies early. That’s the power of small project C4 diagrams: they expose risks before they become crises.
Real-World Example: A Todo App with Purpose
Let’s walk through a simple web-based to-do app. The goal isn’t just to build features—it’s to create a model that communicates intent.
Level 1: System Context
The system has one user: a registered user. It interacts with a database and a third-party email service for reminders.
Key insight: The diagram clarifies that the app is not just a “web app.” It’s a web application with defined external dependencies. This prevents assumptions like “we’ll just mock the email service” during development.
Level 2: Container Diagram
Containers include:
- React-based web frontend (hosted on Vercel)
- Node.js REST API (hosted on AWS Lambda)
- PostgreSQL database (Amazon RDS)
- SendGrid for email delivery
This reveals immediate decisions: Why Vercel? Why AWS Lambda instead of a full server? The diagram forces you to justify choices—and that’s where clarity begins.
Level 3: Component Diagram
Inside the API, components include:
- User Authentication Service
- To-Do Item Service
- Email Notification Service
- Task Scheduler
Now, when someone asks, “Can the email service run independently?”—the answer is visible. The diagram shows it’s a separate component, decoupled from the task scheduler.
By Level 3, you’re not just documenting code—you’re shaping design decisions. The team that used this model caught a dependency loop before it caused a crash. A single email service call was being triggered from the auth flow, creating a feedback loop. The component diagram made it obvious.
Trade-offs in Small Project C4 Diagrams
Not every small project needs all four levels. The key is knowing when to stop.
| Level | Use Case | When to Skip |
|---|---|---|
| Level 1 | Initial stakeholder alignment | When the system is trivial (e.g., a static landing page) |
| Level 2 | Defining technology stack and integration points | When the app has no external dependencies |
| Level 3 | Designing internal structure and responsibilities | For apps with fewer than 3 core services |
| Level 4 | Deep dives into complex logic or critical paths | When no component is reused or performance-critical |
Use this table not as a rule, but as a checkpoint. It helps avoid over-engineering while preserving clarity.
How C4 Prevents Redesigns
One of the biggest costs in software development is rework. In small projects, this often comes from poor communication. A feature request gets misinterpreted because the team didn’t agree on how components interact.
With C4, that’s harder. A single diagram becomes the source of truth. When a new feature is added—say, task due dates—the team asks: Where does this logic belong? Is it part of the task service? Or a new scheduler module?
Without a diagram, they guess. With one, they discuss. The result? Fewer bugs, fewer pull requests, and faster delivery.
Consider this scenario: A mobile app team added a new feature to sync tasks across devices. They didn’t have a C4 diagram. The sync logic ended up in the backend, but also duplicated in the mobile app. Two months later, a bug appeared: updates weren’t synchronized correctly.
After creating a Level 2 container diagram, they realized the sync logic should live in a dedicated service—not spread across devices. They refactored, restored consistency, and avoided future drift.
This is the real value of C4 model real world examples: they turn guesswork into shared understanding.
Practical Tips for Beginners
Here’s how to start with small project C4 diagrams—even if you’re new to modeling:
- Start with Level 1—Who uses the system? What external systems does it interact with? Draw it before writing code.
- Use simple tools—Visual Paradigm, or even pen and paper work fine. The goal isn’t perfection—it’s communication.
- Update with the team—Review diagrams during sprint planning. When a new dependency appears, add it.
- Keep diagrams small—Avoid overloading. If you need more than 6–7 elements, consider breaking it down.
- Link to code—Use comments or annotations to point to actual classes or functions. This bridges the gap between model and implementation.
These steps aren’t just for beginners—they’re for anyone building anything beyond a prototype.
Frequently Asked Questions
Do I need to use all four levels for small projects?
No. Start with Level 1 for stakeholder alignment. Add Level 2 if you have multiple systems or integrations. Level 3 only if you’re managing complex internal logic. Level 4 is optional and best used for critical components.
Can C4 model real world examples help with freelance or solo projects?
Absolutely. Even for solo developers, a C4 diagram acts as a personal design guide. It prevents drift and makes onboarding future contributors easier.
What if my app is too simple to need a C4 diagram?
If your app is a basic form or a static site, a diagram may not be needed. But if it has logic, interactions, or dependencies, even a Level 1 diagram adds value. Clarity is never overkill.
How do I keep C4 diagrams from becoming outdated?
Update them during sprint reviews. Treat them as living artifacts. When a new technology is introduced or a component changes, revise the diagram. Use version control for the files.
Should I share C4 diagrams with non-technical stakeholders?
Yes—but only the top-level diagram. Level 1 is perfect for product managers, clients, or investors. It explains the system without jargon.
Can I use C4 for mobile apps?
Yes. A mobile app typically has a frontend (native or React Native), a backend API, and a database. The same C4 model applies. Use a Level 2 diagram to show how the app interacts with cloud services and local storage.
