Ever since the introduction of World Wide Web in 1990, the domain of web development has evolved dynamically from web pages to web applications. End users no longer browse web pages for reading static content. Websites now have dynamic features to increase their engagement rate. Interactive websites are being developed so users can perform their day to day activities like shopping for groceries, banking, paying taxes, etc. However, these applications are developed by human beings, and, since we’re all human, mistakes happen. Often a simple mistake can impact a critical functionality in your website that will lead the user to go to a different website, reducing your profit and SERP ranking. In this article, we shall discuss the common mistakes made by developers while developing a web application. Using Non-Responsive Design Nowadays, not keeping RWD (Responsive Web Design) in mind will result in a large website displayed in a small screen with small buttons making it difficult for the end user to read the content or click on the horizontal scrollbar along with many other discrepancies, all of which will lead to a bad user experience.