I’ve seen many codebases over the years that come with common warning labels: “this one takes a while to get working”, or “don’t touch that because the whole project will implode”.
I used to think this was purely a symptom of working in high-pressure delivery environments: there’s never enough time to do x, y or z. But even good teams can slowly drift into unhealthy habits if nobody is paying attention. A healthy codebase rarely happens by accident and it’s usually the result of lots of good, small decisions made consistently over time, starting from the initial setup. So, if you’re starting a new project today, or improving an existing one, bear these practices in mind to keep your codebase healthy.
Practical accessibility
Good accessibility is one of the clearest green flags in a project; a project without any consideration for accessibility is a giant red flag. One of the first things I do when testing a website is to try and navigate through it with a keyboard alone. If basic keyboard navigation is broken, chances are that accessibility wasn’t considered during development at all. And of course, if accessibility was overlooked then there are probably other engineering fundamentals missing too.
Good accessibility standards sometimes force teams to make more thoughtful design decisions, but that’s rarely a bad thing in reality. After all, we’re building applications for all users, everyone should be able to use them. If a project sticks to an official WCAG specification, then that tells me everything I want to know.
Code consistency
A project that has clear coding standards from the start is a great sign, so long as they’re being followed and maintained. Linting rules can only take you so far - although they are fairly effective - but having a team that sticks to a plan is a really good sign that the codebase is being looked after. In an ideal world, team members are in constant collaboration via peer review and communication, so nothing radical should find itself in the codebase without the wider team’s blessing. If a new strategy is required, I’d prefer the team discusses it first before it becomes embedded in the codebase.
Consistency ultimately reduces cognitive load; developers shouldn’t have to context-switch every time they open a new file. Everything should feel natural, logical and not a chore.
A confident testing suite
Unfortunately, testing is often one of the first things to be dropped if a project’s resources are stretched, but if they made it into the project and are kept in decent shape then that’s a very good sign.
Unit testing is a fair entry point for testing but I’m less interested in chasing 100% coverage and more interested in whether the important parts of an application are tested, although in an ideal scenario I would want at least 75% code coverage.
Integration tests are also incredibly valuable for more complex features where multiple services interact with each other. They often provide more confidence than isolated tests alone.
End-to-end testing would be ideal too: even a small collection of smoke tests can add a surprising amount of confidence.
Visual regression testing is also increasingly more accessible to projects. Tools like Chromatic make it much easier to catch unintended UI changes before they reach production.
Some people still fail to see the positives of testing applications, clients often don’t until it’s too late. We need to start looking at testing as just another component of the application.
CI/CD quality gates
Humans and computers both make mistakes, but together they can act as a safety net over any project. One of the clearest signs of an unhealthy codebase is when deployments become dreaded events.
I like projects that have automated quality gates that don’t feel like a chore; good CI/CD pipelines should act like guard rails rather than roadblocks. Having sensible Prettier and linting rules goes a long way too. Without any of these in place, your codebase can end up getting messy pretty quickly.
Git hooks are a good way to enforce these quality gates. Personally, I prefer pre-push hooks to pre-commit hooks, just because I like to encourage regular commits and sometimes it just isn’t possible to fix any ‘violations’ in one commit. Any time I’ve used pre-commit hooks in a project, most people tend to commit less often or even worse, bypass the hook altogether. Tooling should encourage good habits, not frustrate developers into working around it. A better dev-first approach is to pre-push, because that assumes a certain level of completion before a pull request is made.
Adding performance budgets with automated checks to your project can work really well in some instances, particularly for modular, component-based codebases. I’ve worked on projects where a single new feature added hundreds of kilobytes to the bundle size, in part due to an added dependency. Having a performance budget in your workflow can - at worst - flag that this is not acceptable, so that it can be refactored to a better state.
Thoughtful documentation
Thankfully, gone are the days where it would take an entire week to get a project running locally. When onboarding new developers, I want them to understand what is going on in the solution but also not feel overwhelmed. If a new developer needs to read a book just to start the application, something has gone wrong.
Coding should generally be self-documenting: good naming conventions, sensible abstractions and clear project structure are far more valuable than excessive comments.
For component-heavy projects, Storybook is a great environment to document your UI in a playable environment (among other many positives such as testing).
It’s following a design system
One sign of a healthy codebase is that the UI feels cohesive and predictable; introducing a design system is about creating a shared language across your design and engineering teams, both working from the same source of truth. When done correctly, it’s the backbone of any healthy project but when done incorrectly it can cause more issues than it’s worth.
Semantic tokens, reusable primitives and consistent styling patterns help prevent the UI from growing chaotic over time. Without these, UI code tends to drift. Slightly different spacing values, colours, typography rules and component layoutst begin to appear everywhere until the frontend doesn’t match the original designs and becomes impossible to manage.
Conclusion
Healthy codebases are good not just for maintainability and developer experience; healthy codebases create confidence and stability. Confidence to deploy and add new features, the stability to make changes without worrying about something imploding.
Most unhealthy codebases don’t become unhealthy overnight: they gradually drift there from rushed decisions, inconsistent standards and short-term thinking. Healthy codebases are built the opposite way: through patience, consistency and lots of small improvements over time.
