Common Mistakes Made by Web Developers and How to Avoid Them

Using Non-Responsive Design

Not keeping RWD (Responsive Web Design) in mind will result in a large website displayed on 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 that lead to a bad user experience.

• Ensure that you target some devices and resolutions before you start developing and writing media queries so that the website is displayed properly on all devices.
• Apart from testing in emulators, test your website in real devices as well to get the feeling of how an end user experiences your website when accessed using a real device.

Refer to the below tutorial on how to perform responsive testing on TestMu AI.

Now you can debug multiple device sizes while performing responsiveness tests simultaneously. Also mark a bug on tools, such as Jira, Trello, Asana, GitHub, etc. LT Browser is the best dev-friendly browser for mobile view debugging on which you can see the mobile view of your website on Android and iOS resolutions.

Key Takeaway: Choosing target devices and resolutions before writing media queries, and then checking the result on real devices as well as emulators, stops a website from reaching phone users as an unreadable desktop layout.

Depending on Website Builder Tools

Many companies nowadays offer tools using which you can easily build a website with drag and drop features. The problem with those tools lies in the backend. Each design decision adds multiple lines of code that makes the website slower and with time, this may cause performance issues and impact critical functionalities.

Slow pages also cost you search visibility. Google scores Core Web Vitals on field data at the 75th percentile, and Interaction to Next Paint replaced First Input Delay as one of those vitals on 12 March 2024. A page needs an INP of 200 milliseconds or less to land in the good band, and a builder that ships scripts you never asked for makes that target harder to hit. Measure the generated page in PageSpeed Insights before you commit to the platform. The same check catches the weight you add yourself: uncompressed images, unminified JavaScript and CSS, and assets served without caching headers are the usual causes of a slow page, and a Lighthouse run in Chrome DevTools names each one.

Watch this video to learn what the Actions Class is in Selenium and how to use it.

• If you do not have enough time for coding, you can purchase templates via Themeforest, Envato or other platforms where at a minimal price, you will get multiple responsive and cross-browser compatible templates that will serve your purpose. You will only need to add the content before launching your website.
• Instead of website builder tools, it is better to use platforms offering content management services like WordPress or Joomla. Apart from the seamless hosting of your website, they will also offer you multiple themes that match the purpose served by your site.

Key Takeaway: Website builder tools trade speed of assembly for page performance, so measure a generated page in PageSpeed Insights first, or use a purchased template or a content management system such as WordPress or Joomla instead.

Using Outdated HTML

Old habits are difficult to get rid of. Earlier versions of HTML did not offer the markup options that make the job easier today. Developers who started out in those days still reach for stacks of nested div and span wrappers and long runs of   entities. That habit inflates the line count and produces layout that breaks in current browsers.

• Update yourself with the current standard and use semantic HTML5 elements such as header, nav, main, article, section, and footer in place of obsolete tags like center and font. Semantic markup keeps the code clean and gives screen readers a structure they can navigate.
• Focus on using HTML to describe your content and use the latest features of CSS3 to design the content's layout.

Key Takeaway: Writing content with semantic HTML5 elements and handling layout in CSS3 keeps markup shorter than stacks of nested div and span wrappers and avoids the rendering breakage that obsolete tags cause in current browsers.

Insufficient Input Validation

Web developers often make the mistake of ignoring form validation and trust on user input. End users are human, and mistakes happen with them also. Incomplete form validation may result in a mistyped alphabet in the phone number field or an incorrect email format missing the '.' or '@'. All these leading to incorrect data submitted by the user that may lead to failed delivery of information to the user's physical or online address.

• Latest front-end frameworks provide outstanding validation rules that are simple to code and can ensure that user input is flawless and according to the format that has been set.
• Implementation of a validation rule is a part of standard coding practice and proper usage of them will result in a quality website preferred by users, thereby, increasing its ranking in the search engine.

Validation is only half of a usable form, and web accessibility is now a compliance requirement as well. The European Accessibility Act applies from 28 June 2025 and covers e-commerce, banking, and transport services together with the websites and apps that deliver them. WCAG 2.2, published as a W3C Recommendation on 12 December 2024, is the checklist most teams work from. Label every input, tie each error message to its field with aria-describedby, and confirm the form works with a keyboard alone.

Key Takeaway: Form validation rules reject a mistyped phone number or a badly formed email address before submission, and the European Accessibility Act, which applies from 28 June 2025, requires those forms to be labelled and usable with a keyboard alone.

Is AI-Generated Code Safe to Merge Without a Security Review?

No. Veracode tested more than 150 large language models on 80 coding tasks and found that only 55 percent of those generations produced secure code. The scan covered Java, Python, C#, and JavaScript. JavaScript passed 57 percent of the time. Cross-site scripting was the weakest category at a 15 percent pass rate, and log injection was worse at 13 percent. Pasting a working snippet from an assistant straight into a form handler or a template is now one of the quickest ways to ship an injection bug.

Read generated code the way you would read a pull request from someone who has never seen your codebase. The OWASP Top 10:2025 is the list to check it against, and the 2025 edition rearranged the order. Software Supply Chain Failures enters at A03, Injection sits at A05, and Mishandling of Exceptional Conditions is a new entry at A10 that covers the error handling most code examples leave out. Escape output on the server rather than trusting a filter that runs in the browser, and repeat every validation rule on the server, because a client side rule is a convenience that a direct HTTP request ignores.

Back the review with a check that runs without you. npm audit submits your dependency list to the registry and returns a report of known vulnerabilities, and the --audit-level config sets the minimum severity at which it exits non-zero, so a build can fail on high and critical findings without stopping for low ones.

Key Takeaway: AI-generated code is not safe to merge without a security review, because Veracode found only 55 percent of generations secure, with cross-site scripting passing 15 percent of the time and log injection 13 percent.

Cross Browser Compatibility Issues

Those days are long gone when Internet Explorer was the only browser available to access websites. Microsoft has retired Internet Explorer, and people now open sites in Chrome, Edge, Firefox, Safari, Samsung Internet, and a long list of other desktop, mobile, and device specific browsers. Browser versions vary widely across that audience, so a layout that renders correctly on your machine can still break on theirs.

• Use analytic tools and target browsers on which your website is meant to run properly. Carry out proper cross browser testing and find out if any usability or functional issue is occurring in any such browser.
• Use cloud testing platforms like TestMu AI which provides you with the opportunity to quickly and seamlessly test your website on multiple browsers simultaneously. Find out any CSS or HTML issues that are causing breakage in any specific browser and fix the issues by replacing them or adding vendor specific codes.

Apart from the mistakes mentioned above, there are other common mistakes like poor content, security issues, poor design, wrong SEO(Search Engine Optimization) techniques, and many others. All of which may lead to your website placed far below in the search engine results. Ensure that these do not happen and your website will be the one preferred by users worldwide.

Key Takeaway: Testing a website across Chrome, Edge, Firefox, Safari, and Samsung Internet catches the CSS and HTML differences that break a layout on browsers other than the one used to build the site.