HTML Validator
Check HTML for common errors and malformed tags.
What is HTML Validator?
The HTML Validator is a fast, browser-based tool that analyzes your HTML markup and surfaces structural errors before they cause rendering issues in production. It checks for unclosed tags, improperly nested elements, missing required attributes, malformed attribute syntax, and other common mistakes that browsers may silently ignore but that can lead to inconsistent layouts or broken accessibility trees.
For developers, having clean and valid HTML is foundational — it ensures predictable cross-browser rendering, improves SEO crawlability, and keeps your DOM structure reliable for JavaScript queries and CSS selectors. Whether you're hand-writing templates, debugging a CMS output, or reviewing auto-generated markup from a framework, a quick validation pass can catch subtle bugs that are otherwise painful to track down by eye.
How to Use
To use the tool, paste your HTML snippet or full document into the input field and trigger the validation. The validator parses the markup and returns a structured list of issues, each annotated with an error type and — where possible — the line and character position of the offending code. Errors are categorized by severity so you can prioritize critical structural problems over minor warnings.
The output highlights issues such as tags opened but never closed (e.g., a missing </div>), elements nested in positions the HTML spec does not allow (e.g., a <p> inside a <span>), attributes written without quotes or with duplicate keys, and self-closing syntax used on non-void elements. The validator works on partial fragments as well as complete documents, so you can validate a component or template partial without wrapping it in a full <!DOCTYPE html> structure.
Keep in mind that the validator checks against the HTML5 specification. Some legacy or proprietary attributes may be flagged as unknown even if they work in your target environment. Additionally, dynamically injected content or server-side template syntax (e.g., Jinja, Handlebars, Blade) should be resolved or stripped before validation, as unresolved placeholders like {{ variable }} may trigger false-positive parse errors.