How to Debug a Website: 9 Best Practices

1. Reproduce the Bug First

Before editing any code, make the bug happen on demand and write down the exact steps, browser, device, and data. A bug you cannot reproduce is a bug you cannot confirm fixed. Once it reproduces, capture it as an automated test that fails, so the same test proves the fix and guards against the bug returning.

2. Read the Console and the Stack Trace

Open the browser's developer tools and read the Console first. Errors, warnings, and uncaught exceptions appear there with a stack trace that points to the file and line where the problem surfaced. Read the stack trace from the top: the first frame in your own code is usually where to start.

3. Check the Network Panel

Many website bugs are failed requests rather than broken code. The Network panel shows every request with its status code, type, and timing. On a product page of the TestMu AI ecommerce playground, the console showed only "Failed to load resource: the server responded with a status of 502 (Bad Gateway)", twice, without naming the resource. The Network panel named it: addthis_widget.js, a third-party sharing script returning 502. The root cause is not in the page's code at all. Oracle ended the AddThis service on May 31, 2023, according to its termination notice, so the fix is to remove the script, not to debug it.

4. Check Syntax and Validate the Markup

Unclosed HTML elements, missing brackets, and typos cause errors that look like logic bugs. Run your code through a linter such as ESLint, and validate the HTML and CSS before debugging deeper. Many editors flag these problems as you type.

• Every bracket, brace, and semicolon is in place.
• Every HTML element that needs a closing tag has one.
• Class names, IDs, and variable names match exactly, including case.

5. Use Breakpoints Instead of console.log

A breakpoint pauses the code on a line so you can inspect every variable and step through the logic one statement at a time. In Chrome DevTools, open the Sources panel, click a line number to set a breakpoint, and reload. Conditional breakpoints pause only when an expression is true, which helps inside loops. You can also add a debugger; statement in the code:

function applyDiscount(total, code) {
  debugger; // execution pauses here while DevTools is open
  return code === "SAVE10" ? total * 0.9 : total;
}

6. Ignore-List Third-Party Scripts

When you step through code, the debugger can wander into framework and library files you do not need to inspect. Chrome DevTools calls the fix the Ignore List: according to Chrome's Ignore List documentation, scripts from /node_modules/ are ignored by default, and you can add your own patterns under Settings, Ignore List, so stepping stays inside your code.

7. Pretty-Print Minified Code and Use Source Maps

Minified production code is hard to read. In the Sources panel, the pretty-print button reformats a minified file so you can set breakpoints in it. Better still, publish source maps from your build so DevTools shows your original files and line numbers, even though the browser runs the minified bundle.

8. Test in the Browsers Your Users Have

A page can work in your browser and break in another because browsers differ in CSS support, default styles, and JavaScript APIs. A CSS reset removes many default-style differences, and checking feature support before using a new CSS property prevents others. For bugs that appear only on a browser or device you do not have, TestMu AI Real-Time Testing opens the site on 3,000+ browser, OS, and device configurations with the matching developer tools in the session, including Chrome DevTools, Firefox DevTools, and Safari Web Inspector.

9. Use AI Assistants, but Verify Every Fix

AI assistants are good at summarizing long logs, explaining an unfamiliar stack trace, and suggesting where to look. They also produce confident fixes that are wrong. Treat an AI suggestion as a hypothesis: reproduce the bug, apply the fix, and confirm with the failing test from step 1. For how AI debugging works and where it falls short, see what AI debugging is.