The Top 10 Mistakes Developers Make When Writing APIs (And How to Fix Them)

APIs are the glue that holds modern software together. They’re the bridges that connect systems, services, and users seamlessly—when done right.

Here are 10 common mistakes developers make when building APIs—and how to fix them before they haunt you (and your users).

1. Skipping Proper Documentation
The Mistake: You build a brilliant API, but the docs are an afterthought. Or worse, nonexistent.

The Fix: Document as you go. Tools like Swagger/OpenAPI or Postman can help auto-generate docs, but you still need to explain things clearly. Include:

• Endpoints
• Request/response examples
• Error codes and their meanings
• Rate limits

Think of your docs as the API’s user manual—a guide that even a newbie dev can follow without crying.

2. Ignoring Versioning
The Mistake: You launch an API without a versioning strategy. Fast forward six months, and your users’ integrations break because you’ve made updates.

The Fix: Always version your API. A simple /v1/ in your endpoints can save everyone a ton of headaches. For breaking changes, roll out a new version and keep the old one running (with clear deprecation timelines).

3. Overloading Endpoints
The Mistake: Your endpoint does everything. One URL, a dozen query params, and a response that’s a JSON labyrinth.

The Fix: Follow the Single Responsibility Principle. Break complex logic into smaller, purpose-specific endpoints. Instead of /getAllData, use /getUsers, /getOrders, and /getProducts for clarity and maintainability.

4. Poor Error Handling
The Mistake: Your API returns a vague 500 Internal Server Error for everything. Helpful? Not at all.

The Fix: Use descriptive error messages. Return clear status codes like:

• 400 Bad Request for invalid input
• 401 Unauthorized for authentication failures
• 404 Not Found when the resource doesn’t exist

Also, include meaningful error messages in the response body to guide users on what went wrong.

5. Not Validating Input
The Mistake: You trust that users will always send well-formed requests. Spoiler: they won’t.

The Fix: Validate everything. Use libraries like Joi (Node.js), Marshmallow (Python), or built-in validation features in frameworks like Spring Boot or .NET. Validate query params, request bodies, and headers to prevent malformed data or security vulnerabilities.

6. Ignoring Rate Limiting
The Mistake: A single user can send a flood of requests, potentially crashing your system.

The Fix: Implement rate limiting. Use tools like Redis or API gateways to cap the number of requests per user/IP. For example:

• 100 requests per minute
• Return 429 Too Many Requests when the limit is exceeded

Bonus: Communicate limits in the headers (X-RateLimit-Limit, X-RateLimit-Remaining).

7. Inconsistent Naming Conventions
The Mistake: Your endpoints are a mix of snake_case, camelCase, and kebab-case. Consistency? What’s that?

The Fix: Pick one convention and stick to it. Most APIs favor snake_case for parameters and camelCase for JSON keys. Consistency improves readability and reduces onboarding friction for users.

8. Forgetting About Security
The Mistake: You expose sensitive data or skip authentication because "it’s just for internal use."

The Fix: Treat every API as if it’s public. Best practices include:

• Use HTTPS to encrypt data in transit.
• Implement OAuth2 or token-based authentication.
• Avoid exposing sensitive data in error messages or logs.

Remember, security isn’t optional; it’s fundamental.

9. Returning Too Much Data
The Mistake: Your API fetches massive datasets when users only need a few fields.

The Fix: Implement pagination and field filtering. Let users specify:

• Which fields they need (?fields=name,email)
• Page size and number (?page=2&pageSize=50)

This keeps responses lightweight and speeds up performance.

10. Not Testing Enough
The Mistake: You ship an API without thorough testing, assuming it’ll "just work."

The Fix: Automate testing with tools like Postman, Newman, or Jest (for Node.js). Cover:

• Unit tests: Validate individual endpoints.
• Integration tests: Check how your API interacts with other systems.
• Load tests: Simulate high traffic to ensure scalability.

Your API should pass these tests before seeing the light of day.

Think of your API as a product, not just a backend feature. Treat it with the same level of care, and your users will thank you.

What’s one API mistake you’ve encountered (or made) that drives you up the wall? Let me know in the comments!

Comments

[FlipperZeroUnleashed]

Writing APIs can be tricky, and common mistakes include poor documentation, inconsistent naming conventions, and lack of proper error handling. To improve, focus on clear documentation, standardize your API structure, and ensure robust error responses. Avoid these pitfalls to create reliable and user-friendly APIs. For tech tools and insights, check out FlipperZeroUnleashed for resources to streamline your development process.