HTML Formatter & Validator
Format, prettify, and validate HTML5 code instantly in your browser. Paste minified, messy, or framework-generated HTML to get back clean, consistently indented markup — with unclosed tags, nested block elements inside inline tags, and structural errors highlighted by line number.
Format, prettify, and validate HTML5 code instantly in your browser. Paste minified, messy, or framework-generated HTML to get back clean, consistently indented markup — with unclosed tags, nested block elements inside inline tags, and structural errors highlighted by line number.
This tool is designed to provide a seamless experience for developers by handling complex operations directly in your browser with maximum speed and security.
HTML — HyperText Markup Language — is the structural language of every web page. It defines what content exists on a page and how elements relate to each other: which text is a heading, which content is a list, which region is a navigation bar, which content is the main article. Browsers parse HTML into a Document Object Model (DOM) tree — a hierarchical representation where every element is a node with parent, child, and sibling relationships. The visual rendering and interactive behavior of a page are built on top of that DOM tree by CSS and JavaScript respectively.
HTML is forgiving in a way that creates a specific kind of problem. Browsers have a built-in error recovery algorithm (defined by the HTML5 parsing specification) that attempts to fix malformed HTML rather than displaying an error page. A missing closing tag, a misplaced element, or an attribute without quotes — browsers will try to render something sensible. But the rendered result may not be what you intended, and the DOM the browser constructed from your malformed HTML may be structurally different from what you wrote, causing JavaScript selectors to fail, CSS styles to not apply to the elements you expected, and accessibility tools to misread the page structure.
HTML formatting means applying consistent indentation that reflects the actual nesting structure of the document — child elements indented relative to their parent elements. This makes the parent-child relationships visible at a glance, makes it easy to identify the opening and closing tags of any element, and makes structural errors like unclosed tags immediately obvious because the indentation level stays open when you would expect it to close. Formatted HTML is not just easier to read — it actively reveals structural problems that are invisible in a wall of unformatted markup.
Read the Full GuideThis tool takes raw, minified, or inconsistently indented HTML and produces clean, consistently formatted markup. It parses the HTML into a tree structure, identifies every element and its nesting level, and outputs the markup with proper indentation — child elements indented by two spaces relative to their parent, closing tags on their own lines for block elements, and inline elements kept on one line with their content when appropriate. The output is semantically identical to the input — no content is changed, only whitespace and indentation. The validator component checks the HTML structure for common errors as it parses. Unclosed tags are reported with the line number where the opening tag appeared. Attributes missing their closing quotes are flagged at the specific attribute. Block-level elements incorrectly nested inside inline elements — a div inside a span, for example, which is invalid HTML — are reported. Elements that are not valid in their context (a td outside a table, a li outside a ul or ol) are identified. The validator reports the specific error, the element involved, and the line number, giving you the precise location to fix rather than a generic "invalid HTML" message. The tool handles both HTML fragments and complete HTML documents. If you paste a complete document with DOCTYPE, html, head, and body elements, it formats the entire document. If you paste a component template — just the markup for a React component or an Angular template — it formats the fragment without requiring the full document context. This is particularly useful for working with component-based frameworks where you write HTML fragments rather than complete pages. Framework-generated or server-side-rendered HTML that has been minified for production can be pasted directly into the formatter to restore readable structure for debugging.
1. Paste your HTML into the Input HTML field — this can be a complete HTML document with DOCTYPE and html tags, a partial HTML fragment like a component template, or minified HTML copied from a page source. Click Load Example if you want to see a well-structured sample document before using your own HTML. There is no size limit for the input — large HTML files with hundreds of elements format correctly.
2. Click Format HTML Output — the tool parses the HTML, builds the element tree, and applies consistent two-space indentation based on the nesting depth of each element. Block elements like div, p, section, article, ul, and li each start on a new line with appropriate indentation. Inline elements like span, a, strong, and em stay on the same line as their content when they appear inside block elements. Void elements like br, hr, img, and input are correctly written as self-closing.
3. Review the formatted output — check the indentation structure to verify that the nesting is what you intended. An element that is indented deeper than expected may be inside the wrong parent. An element at the same indentation level as its intended parent may be outside it due to a missing closing tag in the original HTML. The formatted output makes these structural relationships immediately visible.
4. Read any validation errors in the results — if the HTML has structural problems, the tool reports each error with the element name and the line number in the original input where the issue was detected. Common reported errors include unclosed tags, attributes missing their closing quotes, block elements inside inline elements, and table structure violations like td outside tr or tr outside table.
5. Copy the formatted HTML using the Copy button and paste it back into your code editor, template file, or wherever the HTML lives — the formatted output is ready to use directly. If you are debugging minified production HTML, the formatted version is for reading only — keep your build process and only use the formatter to understand the structure.
The most disorienting HTML debugging experience is when the browser renders something visually different from what the markup appears to specify, and you cannot figure out why. You open DevTools, inspect the element, and the DOM structure shown in the Elements panel is completely different from the HTML you wrote — because the browser's error recovery algorithm silently restructured your malformed markup into something it could render. The place to start is always to format the HTML and look at the indentation. A div that was never closed shows up as a permanently open indentation level. A table row outside a table body appears at an unexpected nesting level. Formatting makes these structural errors visible before you start chasing the wrong bug in CSS or JavaScript. For front-end developers working with component-based frameworks like React, Vue, or Angular, HTML formatters are essential for one specific workflow: debugging the server-side rendered output of a page. Your framework produces a bundle of minified HTML that the browser executes perfectly, but when something goes wrong — a hydration mismatch, a missing element, an unexpected DOM structure — you need to read the actual rendered HTML. Copy the page source, paste it into the formatter, and the minified wall of characters becomes navigable, indented markup you can actually read and debug. Email HTML is another constant use case. HTML for email clients is notoriously complex — you are writing table-based layout for Outlook's Word rendering engine while also supporting modern email clients, with inline styles, conditional comments for Outlook, and deeply nested table structures. Email HTML is almost never hand-formatted because it is generated by tools, and reading the generated output to debug rendering issues requires a formatter. Paste the generated email HTML, format it, and the nested table structure becomes readable enough to identify which table cell is causing the rendering problem.
Precise error location — reports unclosed tags missing attribute quotes and structural violations with exact line numbers rather than generic invalid HTML messages
Handles both complete documents and fragments — formats full HTML documents with DOCTYPE and also partial component templates or HTML snippets without requiring the full document wrapper
Block vs inline element awareness — correctly formats block elements on their own lines with indentation while keeping inline elements and their content together
Minified HTML support — formats production-minified HTML from server-side-rendered React Vue Angular and other frameworks back into readable indented markup
HTML5 compatible — supports the full HTML5 element set including semantic elements like article section nav aside main figure and figcaption
100% browser-based — your HTML markup including proprietary template code sensitive content and internal tool interfaces never leaves your machine
Instant formatting — all parsing and formatting runs locally in your browser with no server round-trip
works for files of any size
No installation or account required — paste HTML and format immediately with no setup or sign-in
Formatting minified server-side-rendered HTML from React Vue or Angular for debugging DOM structure issues
Validating HTML templates for unclosed tags and structural errors before deploying to production
Formatting email HTML templates generated by tools like MJML or campaign builders for debugging layout issues in email clients
Cleaning up HTML copied from design tools like Figma that generates messy markup
Formatting HTML fragments from component libraries to understand the actual DOM structure they produce
Validating HTML documentation and static site content for structural errors before publishing
Debugging hydration mismatch errors in SSR frameworks by formatting the rendered page source
Formatting legacy HTML from older codebases to understand element nesting and identify structural debt
Example Input
<!DOCTYPE html><html><head><title>Example</title></head><body><h1>Hello World</h1><p>This is a <b>formatted</b> HTML snippet.</p><ul><li>Item 1</li><li>Item 2</li></ul></body></html>
Example Output
<!DOCTYPE html>
<html>
<head>
<title>Example</title>
</head>
<body>
<h1>Hello World</h1>
<p>This is a <b>formatted</b> HTML snippet.</p>
<ul>
<li>Item 1</li>
<li>Item 2</li>
</ul>
</body>
</html>Unclosed Tags: An opening tag does not have a corresponding closing tag. For example a div that is opened but never closed will leave all subsequent content nested inside it indefinitely in the DOM. The validator reports the line number of the opening tag that was never closed. Fix: add the missing closing tag at the appropriate nesting level. Check that every opening div, span, section, article, nav, header, footer, main, aside, p, ul, ol, table, and other non-void element has a matching closing tag.
Invalid Attributes: Attribute values must be wrapped in double quotes in HTML5. An attribute like class=container without quotes around the value is invalid and may be misinterpreted by some parsers. An attribute with an illegal character — a greater-than sign inside an attribute value without encoding, or an attribute name containing a space — will cause the parser to misread the element boundary. Fix: always wrap attribute values in double quotes and use HTML entities for special characters inside attribute values.
Missing DOCTYPE: HTML documents should begin with the DOCTYPE declaration. Without it, browsers enter quirks mode — a legacy rendering mode that exists for backward compatibility with pre-standards HTML. Quirks mode affects box model calculations, table rendering, and numerous CSS behaviors in ways that can make your layout behave differently across browsers. Fix: add <!DOCTYPE html> as the very first line of any complete HTML document.
Block Elements Inside Inline Elements: HTML defines two content model categories: block-level elements (div, p, section, article, ul, table) and inline elements (span, a, strong, em, img). Placing a block element inside an inline element is invalid HTML — for example a div inside a span. Browsers will attempt to recover but may restructure the DOM in unexpected ways. Fix: restructure the markup so block elements are only children of other block elements or the body, and inline elements are only children of block elements or other inline elements.
Table Structure Violations: HTML tables have a strict required nesting structure: table contains thead, tbody, or tfoot, which contain tr, which contain th or td. Skipping levels — placing a td directly inside a table without a tr, or placing a tr directly inside a table without tbody — is invalid and causes browsers to insert the missing elements automatically, which may not produce the structure you intended. Fix: always follow the complete table nesting hierarchy and include tbody explicitly rather than relying on implicit insertion.
Assuming that HTML which renders correctly in the browser is valid HTML
Fix: Browsers are extremely forgiving parsers — they silently fix unclosed tags, misplaced elements, missing quotes, and many other errors before rendering. A page can look perfect in Chrome and still have invalid HTML that causes problems in screen readers, search engine crawlers, or other browsers that apply error recovery differently. Valid HTML is not just about visual rendering — it is about creating a DOM structure that is predictable, accessible, and correctly interpreted by all consumers of the page including assistive technologies and search engines. Use the validator to check HTML that renders fine but may have underlying structural issues.
Using div and span for everything instead of semantic HTML5 elements
Fix: Div and span are generic container elements with no semantic meaning. HTML5 introduced semantic elements — article, section, nav, header, footer, main, aside, figure, figcaption, time, mark — that convey the purpose of the content they contain. Using these elements instead of divs with class names makes your HTML more meaningful to search engines (better SEO), more accessible to screen readers (which use element roles derived from semantic elements), and more maintainable (the element name itself documents its purpose). A formatter cannot fix this for you, but it makes the structure visible so you can identify where generic divs could be replaced with appropriate semantic elements.
Writing self-closing syntax on non-void elements in HTML5
Fix: In HTML5 (as opposed to XHTML), only void elements — elements that cannot have children — are self-closing: br, hr, img, input, meta, link, area, base, col, embed, param, source, track, wbr. Writing a div as <div/> or a p as <p/> in HTML5 is invalid — the slash is silently ignored by the HTML parser and the element is treated as an opening tag requiring a closing tag. This is different from XHTML and from JSX where all elements must be explicitly closed. In HTML5, use the full closing tag for non-void elements and omit the slash on void elements.
Not encoding special characters in HTML content and attributes
Fix: The characters less-than, greater-than, ampersand, and double quote have special meaning in HTML markup. If these characters appear in text content or attribute values without being encoded as HTML entities, the parser may misinterpret them as markup boundaries. Less-than in text content that the browser parses as an opening tag is a classic XSS vector as well as a rendering bug. Always encode: less-than as < greater-than as > ampersand as & double quote inside attribute values as ". These encodings are handled automatically by template engines and frameworks, but raw HTML requires manual encoding of special characters.
Using inline styles instead of CSS classes for maintainability
Fix: The HTML formatter makes inline styles very visible — style attributes on individual elements appear explicitly in the formatted markup. If you see many elements with inline style attributes after formatting, that is a signal that the styling approach needs refactoring. Inline styles override CSS cascading rules, cannot be reused across elements, cannot be targeted by CSS media queries or pseudo-classes, and make the HTML harder to maintain. For anything beyond truly one-off dynamic styles set by JavaScript, move styling to CSS classes. The formatter itself does not fix this, but the formatted view makes the problem visible in a way that dense unformatted markup does not.
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Does it support HTML5?
Yes. The formatter and validator are fully compatible with the HTML5 specification. All HTML5 semantic elements — article, section, nav, header, footer, main, aside, figure, figcaption, time, mark, details, summary, dialog, and others — are recognized and formatted correctly. HTML5 void elements (br, hr, img, input, meta, link, and others) are handled as self-closing without requiring the XHTML-style trailing slash. The DOCTYPE html declaration is recognized and preserved.
Can it handle large HTML files?
Yes. The formatter handles HTML files of any size — large page templates, server-side-rendered page sources with hundreds of elements, or minified HTML files that expand to thousands of lines when formatted. Performance depends on the size of the input and your device hardware, but typical page HTML in the range of 10,000 to 50,000 characters formats in under a second. For very large files like full website page sources, formatting may take a moment but completes correctly.
Is it safe for sensitive HTML templates?
Yes. All formatting and validation runs entirely in your browser — your HTML markup, including any internal tool interfaces, admin dashboard templates, proprietary component code, or content containing sensitive information, never leaves your machine and is never transmitted to any server. This is important for developers working on internal tools or products where the HTML structure itself reveals information about the product's functionality.
What is the difference between HTML formatting and HTML validation?
HTML formatting fixes the visual presentation of the markup — indentation, line breaks, and whitespace structure — to make it easier to read and understand. Formatting does not check whether the HTML is structurally correct. HTML validation checks whether the elements, nesting, and attributes follow the HTML specification rules — unclosed tags, invalid nesting, missing required attributes, deprecated elements. This tool does both: formatting makes the HTML readable and validation checks it for structural errors. You can format without any errors being reported if the HTML is well-formed but inconsistently indented.
Why does my HTML validate here but look wrong in the browser?
HTML validation checks structural correctness according to the specification. The browser rendering engine adds additional interpretation on top of valid HTML — CSS specificity, inherited styles, browser default stylesheets, and JavaScript interactions all affect what you see. A page can have perfectly valid HTML and still render incorrectly due to a CSS issue, a JavaScript error, or a missing external resource. If your HTML validates clean and still renders wrong, the problem is in CSS or JavaScript rather than HTML structure. Use browser DevTools to inspect the applied styles and identify the rendering issue.
Can I use this to validate HTML from React, Vue, or Angular templates?
Yes, with an important clarification. React JSX, Vue templates, and Angular templates use HTML-like syntax but are not standard HTML — they include component tags, template directives, and expression syntax that are not valid HTML. Copy just the standard HTML portion of a template (ignoring framework-specific attributes like v-if, ng-if, or @click) to validate the underlying HTML structure. For validating the complete framework template syntax, use the framework-specific linting tools: eslint-plugin-react for JSX, vue-eslint-parser for Vue templates, and the Angular template type checker for Angular.
How do I fix unclosed tag errors in my HTML?
The validator reports the line number where the opening tag appeared that was never closed. Go to that line in your HTML and find the element. Then look at the content that should be inside that element and find where the closing tag should be placed — it should appear immediately after the last child element that belongs inside the unclosed element, before the next sibling element at the same level. The formatted output from this tool is particularly helpful for finding unclosed tags — an element that stays open appears as an increased indentation level that never decreases back to the expected level, making the missing close visually obvious.
Does it validate accessibility issues like missing alt attributes?
The validator checks structural HTML validity according to the HTML specification — unclosed tags, invalid nesting, illegal elements, malformed attributes. It does not check accessibility rules like missing alt attributes on images, missing aria labels on interactive elements, or insufficient color contrast. For accessibility validation, use dedicated tools: the axe DevTools browser extension for automated accessibility testing, WAVE by WebAIM, or the built-in accessibility auditor in Chrome DevTools Lighthouse. HTML structural validity is a prerequisite for accessibility but does not guarantee it — a page can be structurally valid HTML and still have significant accessibility problems.
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