Modern applications rely heavily on APIs. Whether it’s a mobile app, SaaS platform, ERP system, or AI-powered application, APIs are the bridge that connects everything together.

Building a simple API is easy. Building a scalable, secure, and maintainable API is much harder.

Many developers focus only on making endpoints work, but in real-world production systems, poorly designed APIs can lead to:

security vulnerabilities

slow performance

difficult maintenance

frontend integration issues

unexpected production crashes

In this blog, we’ll explore some of the most common mistakes developers make while building APIs and how to avoid them.

1. Mixing All Logic Inside Controllers

One of the most common mistakes is putting all business logic directly inside route handlers or controllers.

Example:

app.post('/users', async (req, res) => { // validation // database queries // email sending // business logic // response handling })

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At first, this looks manageable.…