How can you ensure data validation in an API implemented using Flask or Express?

Data validation in APIs is essential for security and reliability. Using middleware for input validation is a common approach in Flask and Express. Middleware allows you to intercept and validate incoming data before it reaches your API's endpoints, reducing the risk of accepting malicious or invalid data. Client-side validation is not sufficient for security, and avoiding validation can lead to vulnerabilities. Manually validating data for each request can be error-prone and inefficient.