5 Mistakes Developers Make When Designing APIs

APIs are the backbone of modern applications — whether it’s powering a mobile app, enabling integrations between services, or scaling distributed systems. A well-designed API feels almost invisible: easy to consume, predictable, and stable. But many developers, especially when starting out, fall into the same traps that make APIs confusing, fragile, or hard to maintain.

In this post, I’ll walk through 5 common mistakes developers make when designing APIs, and how you can avoid them.

1. Ignoring Consistency in Naming and Structure

One of the first signs of a poorly designed API is inconsistent naming conventions. Imagine calling one endpoint /getUser and another /orders/list. Not only does it confuse clients, but it also makes long-term maintenance painful.

👉 What to do instead:

• Stick to RESTful resource-based naming: /users/{id}, /orders/{id}.

• Use plural nouns (/users, /products) rather than verbs (/getUser).

• Follow one convention and enforce it across the entire API.

Consistency builds trust—developers consuming your API should be able to guess the next endpoint without checking documentation.

2. Overloading APIs With Too Much Responsibility

A common mistake is creating “God endpoints” that try to do everything. For example, an endpoint like /processDataAndNotifyAndSave couples multiple business concerns together.

👉 Why it’s a problem:

• Hard to debug when something breaks.

• Difficult to evolve — changing one part risks breaking others.

• Bloats response payloads unnecessarily.

👉 Better approach:

• Follow Single Responsibility Principle at the API level.

• Break down actions into smaller, well-defined endpoints (/process, /notify, /save).

• Compose functionality at the service layer, not inside the endpoint.

3. Poor Error Handling

Nothing frustrates developers more than getting a generic 500 Internal Server Error without context. Or worse, inconsistent error formats across endpoints.

👉 What to do instead:

• Use proper HTTP status codes:

  • 200 OK for success

  • 400 Bad Request for invalid input

  • 401 Unauthorized for auth issues

  • 404 Not Found for missing resources

  • 500 Internal Server Error only when truly unexpected

• Return structured error responses (e.g., JSON):

Clear error handling saves time for consumers and reduces support overhead for you.

4. Not Thinking About Versioning Early

Many APIs start small and simple—but as products evolve, new features and breaking changes become unavoidable. If you don’t plan for versioning upfront, you risk breaking existing clients.

👉 How to fix it:

• Add versioning strategy early (/v1/users, /v2/users).

• Use headers or query params if you prefer more flexibility.

• Deprecate old versions gradually, giving clients time to migrate.

Good APIs grow with their products—bad APIs get abandoned.

5. Ignoring Documentation and Developer Experience

Even the most beautifully designed API is useless if nobody knows how to use it. Many developers treat documentation as an afterthought, dumping a few notes in a README.

👉 Why it matters:

• Clear docs = faster adoption.

• Reduces support requests.

• Improves credibility of your API.

👉 Best practices:

• Provide examples for requests & responses.

• Keep docs updated whenever the API changes.

• Use tools like Swagger/OpenAPI to auto-generate interactive docs.

Final Thoughts

Designing APIs isn’t just about making things “work.” It’s about creating interfaces that other humans can understand, trust, and build upon. Avoiding these five mistakes—consistency, responsibility, error handling, versioning, and documentation—will help you create APIs that scale smoothly and delight developers.

If you’re a backend engineer (like me) who loves building clean, scalable systems, remember: a great API is your product’s handshake with the world. Make it strong and professional.