HTML Validator

Free Online HTML Validator

This page provides six browser-based HTML validation and analysis utilities accessible from the left sidebar. Every tool runs entirely in your browser. No data is uploaded to any server, no account is required, and nothing is stored. Select a tool, paste your HTML code or upload an .html file, and the results appear immediately. All tools support drag-and-drop file upload for quick processing.

Online Free HTML Validator with Health Score

The HTML validator on this page goes beyond simple syntax checking. When you paste or upload your HTML code, the validator runs a full structural analysis and displays the results in a dashboard-style panel. A health score from 0 to 100 gives you an instant quality rating. Errors deduct 15 points each and warnings deduct 5 points each. A quick-check grid at the top of the results panel shows pass or fail status for DOCTYPE, charset, lang attribute, viewport, title, and tag matching. Below the grid, every issue is listed with its severity icon, line number, description, and rule category.

What the HTML Validator Checks

The validator inspects document structure including DOCTYPE declaration, html, head, body, and title elements. It verifies that every opening tag has a matching closing tag. Void elements like br, img, input, and meta are handled correctly. Image accessibility is checked by verifying alt attributes on every img element. Duplicate id attributes are detected and reported with all line numbers where the duplicate appears. Links with target="_blank" are flagged when they are missing rel="noopener noreferrer" for security. Recommended meta tags for charset and viewport are checked and reported when missing.

File Upload and Drag-and-Drop

All tools support three input methods. You can paste HTML directly into the code editor, click the Upload HTML button to select a file from your computer, or drag and drop an .html, .htm, or .txt file onto the editor panel. The file is read locally using the browser FileReader API. No data leaves your device at any point.

Accessibility Checker for HTML

The Accessibility Check tool scans your HTML for common WCAG 2.1 Level A violations. It checks that every img element has an alt attribute and flags images with empty alt that are not marked with role="presentation" or aria-hidden. Form inputs, selects, and textareas are checked for associated labels or aria-label attributes. Buttons are verified to have visible text or an aria-label. The html element is checked for a lang attribute. The tool also verifies that your document has an h1 element and reports any heading level skips, such as an h2 followed directly by an h4.

Why Accessibility Matters

Accessible HTML ensures your content works for all users, including those using screen readers, keyboard navigation, and other assistive technologies. Many of these checks are also legal requirements under the ADA, EN 301 549, and similar regulations in various countries. Fixing accessibility issues also improves your SEO because search engines consider many of the same structural qualities when ranking pages.

Meta Tag Inspector for SEO Analysis

The Meta Inspector analyses the head section of your HTML document and reports on all elements that affect search engine visibility and social media sharing. It checks whether a title tag exists and reports its character count with a recommendation to keep it under 60 characters. It checks for a meta description and flags it if missing or over 160 characters. Charset and viewport meta tags are verified. The inspector also checks for four Open Graph properties (og:title, og:description, og:image, og:url) and for a canonical link element. Every finding is displayed with its status so you can quickly identify what is missing.

Link Checker and Tag Counter

The Link Checker tool analyses every anchor tag in your HTML and provides a complete breakdown. It shows total links, internal links, external links, anchor links, and empty links. Each link is examined for common issues: missing href attribute, missing visible text or aria-label, and target="_blank" without rel="noopener noreferrer". The Tag Counter tool takes a different approach and lists every HTML tag type found in your document with its occurrence count, sorted from most frequent to least. It shows the total number of tags and the number of unique tag types, which is useful for understanding the complexity of a document and identifying overuse of specific elements.

Heading Outline Viewer

The Heading Outline tool extracts all h1 through h6 elements from your HTML and displays them in an indented tree that mirrors the heading hierarchy. Each heading shows its level, line number, and text content. Skipped heading levels are flagged with a warning. This tool is valuable for content editors and SEO specialists who need to verify that a page has a logical document outline before publishing. A well-structured heading hierarchy helps screen readers navigate your content and helps search engines understand the topical structure of your page.

Privacy and Browser-Only Processing

Because all validation and analysis happens locally in your browser, your HTML code never leaves your device. This makes these tools safe to use with production code, proprietary templates, client projects, and HTML that contains sensitive content. No data is transmitted to any server, no cookies are set, and no account or signup is required.

Related Online HTML and Web Development Tools

If you work with HTML validation and web development regularly, these other free tools on the site complement this page:

• HTML Minify -- minify, expand, validate, and transform HTML code with configurable options
• HTML Beautifier -- beautify, minify, validate, and transform HTML code
• HTML Formatter -- format, minify, validate, extract text, and encode entities
• HTML Linter -- lint and check HTML for common code quality issues
• HTML Checker -- check HTML structure and validate document integrity
• HTML Editor -- full CodeMirror editor with live preview and HTML validator
• HTML Pretty Print -- pretty print, compact, lint, and transform HTML code
• Code Formatter -- format HTML, CSS, JSON, XML, and JavaScript in one tool