Validate Your HTML Code Online Validate HTML structure with checks for unclosed tags, nesting errors, and common mistakes.

The tool uses a regular expression to parse the input HTML string, identifying all tags and storing their names in a set for efficient lookups. It then iterates through the matched tags, using a stack data structure to track opening and closing tags, ensuring proper nesting and balance. If a closing tag is encountered without a matching opening tag, or if an opening tag is not closed, it adds an error message to the details array. The tool also checks for specific structural elements, such as the presence of a DOCTYPE declaration, html, head, and body elements, and warns about their absence if necessary. Additionally, it checks for deprecated tags like font and center, and img tags without alt attributes, adding warnings to the result object. The validation result is then returned as an object containing arrays of details and warnings, providing detailed information about the validated HTML code.

The tool's implementation relies on React state management, using the useState hook to store the input HTML string and the validation result, and the useCallback hook to memoize the handleValidate function. When the user clicks the Validate button, it calls the validateHtml function, passing the current input string, and updates the result state with the returned validation object. The tool then renders the validation result, displaying details and warnings in a formatted list, using TypeScript type annotations to ensure correctness of the result object's properties.

The validation algorithm itself is implemented in the validateHtml function, which takes an HTML string as input and returns an object containing validation results. It uses JavaScript's built-in string methods, such as trim and split, to preprocess the input string, and then applies regular expressions to extract tag names and attributes. The tool also uses a set of predefined deprecated tags to check for their presence in the input HTML code. By combining these techniques, it provides an efficient and accurate way to validate HTML structure and detect potential issues.