HTML Validator Online

This free online HTML validator lets you validate your files as the w3c standards. The HTML Validator is a free tool we created to help you write clean and correct HTML code. When building a webpage, it’s easy to make a small mistake, like forgetting to close a tag or using a duplicate ID. But even tiny errors can mess up your page’s layout or how it appears on different devices. This tool is here to help you find those problems quickly.

HTML Validator Online

Upload, paste, or load a URL. Validate with HTMLHint. Export results or download your HTML.

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Validation Results

Tip: URL loading may be blocked by CORS; consider a server proxy for external sites. Clipboard actions need user interaction and secure contexts (HTTPS).
` const $code = $("#codeInput"); const $lines = $("#lineNumbers"); const $results = $("#results"); const $summary = $("#summary"); const $status = $('#opStatus'); // Line numbers rendering function updateLineNumbers() { const text = $code.val(); const count = (text.match(/\n/g) || []).length + 1; let buf = ""; for (let i = 1; i <= count; i++) buf += i + (i === count ? "" : "\n"); $lines.text(buf); } $('#sampleBtn').on('click', function () { $code.val(''); $code.val(sample); updateLineNumbers() }) $code.on("input", updateLineNumbers); $code.on("scroll", function () { $lines.parent().scrollTop($code.scrollTop()); }); // Initialize updateLineNumbers();// File upload $('#uploadBtn').on('click', function () { fileInput.value = ''; $("#fileInput").click(); }); $("#fileInput").on("change", function (e) { const file = e.target.files[0]; if (!file) return; const reader = new FileReader(); reader.onload = () => { $code.val(reader.result); updateLineNumbers(); flashSummary("Loaded File: " + file.name); }; reader.readAsText(file, "utf-8"); });// Load URL $('#loadUrlBtn').on('click', async function () { const url = prompt('Enter the URL to Load HTML Code'); if (!url) return; $status.text('Fetching...'); // const url = $("#urlInput").val().trim(); if (!url) { flashSummary("Enter a valid URL to load.", true); return; } try { const res = await fetch(url, { mode: "cors" }); if (!res.ok) throw new Error("HTTP " + res.status); const html = await res.text(); $code.val(html); updateLineNumbers(); flashSummary("Loaded URL: " + url); } catch (err) { flashSummary("Failed to Load URL: " + err.message, true); } $status.text(''); });// Copy $("#copyBtn").on("click", async function () { try { await navigator.clipboard.writeText($code.val()); $status.text('Copied to Clipboard'); flashSummary("Copied to Clipboard."); setTimeout(() => $status.text(''), 2000); setTimeout(() => flashSummary(''), 2000); } catch (err) { flashSummary("Clipboard Copy Failed: " + err.message, true); } });// Paste $("#pasteBtn").on("click", async function () { try { const text = await navigator.clipboard.readText(); if (!text) { flashSummary("Clipboard is Empty.", true); return; } $code.val(text); updateLineNumbers(); flashSummary("Pasted from Clipboard."); setTimeout(() => flashSummary(''), 2000); $status.text('Pasted From Clipboard'); setTimeout(() => $status.text(''), 2000); } catch (err) { flashSummary("Clipboard Paste Failed: " + err.message, true); } });// Clear $("#clearBtn").on("click", function () { $code.val(""); updateLineNumbers(); $results.empty(); $summary.text(""); });// Validate $("#validateBtn").on("click", function () { const html = $code.val(); flashSummary("Write or Paste Your HTML Code in Textarea."); if (!html) return; const errors = HTMLHint.HTMLHint.verify(html, defaultRules); renderResults(errors); });// Export errors $("#exportErrorsBtn").on("click", function () { const html = $code.val(); const errors = HTMLHint.verify(html, defaultRules) || []; const dataStr = "data:text/json;charset=utf-8," + encodeURIComponent(JSON.stringify(errors, null, 2)); const a = document.createElement("a"); a.setAttribute("href", dataStr); a.setAttribute("download", "html-errors.json"); document.body.appendChild(a); a.click(); a.remove(); flashSummary("Exported Errors to JSON."); });// Download HTML $("#downloadHtmlBtn").on("click", function () { const blob = new Blob([$code.val()], { type: "text/html;charset=utf-8" }); const url = URL.createObjectURL(blob); const a = document.createElement("a"); a.href = url; a.download = "document.html"; document.body.appendChild(a); a.click(); a.remove(); URL.revokeObjectURL(url); flashSummary("Downloaded HTML."); });// Render results function renderResults(errors) { $results.empty(); if (!errors.length) { $summary.html("Congratulations! No Errors or Warnings Found. Your HTML is Valid ✓"); return; } $summary.html(errors.length + " Issue" + (errors.length > 1 ? "s" : "") + " Found."); errors.forEach(err => { const $item = $("
").addClass("result-item"); const severity = err.type || "error"; // 'error' or 'warning' const lineInfo = "Line " + (err.line || "?") + ", Col " + (err.col || "?"); const rule = err.rule && err.rule.id ? err.rule.id : "rule"; const $meta = $("
").addClass("meta").append( $("").addClass(severity+" badge").text(severity.toUpperCase()), $("").text(lineInfo), $("").text("Rule: " + rule) ); const $msg = $("
").addClass("msg").text(err.message || "Issue"); $item.append($meta, $msg); $results.append($item); }); }// Helpers function flashSummary(msg, isError) { $summary.text(msg).css("color", isError ? getCssVar("--error") : getCssVar("--muted"));$summary.stop(true, true).fadeOut(50).fadeIn(150); } function getCssVar(name) { return getComputedStyle(document.documentElement).getPropertyValue(name).trim(); }

You can paste your code into the editor, and our tool will check it against the official standards. It points out syntax errors, bad practices, and other common issues. Using this HTML checker helps ensure your website is well-built, accessible, and works reliably for all your visitors.

How HTML Validator Works

  • Paste your HTML code into the text area above or open an HTML file or Load by URL.
  • Click the “Validate” button.
  • The tool will immediately check your code and show a list of any errors or warnings.
  • Each item in the list explains the issue and shows you the line and column number where it happened.
  • Error Type and it’s color will show the importance of HTML Code mistake. A (ERROR) better to solved. B (WARNING) will not heart your webpage but for SEO need to fix.
  • If your code is perfect, you’ll see a success message!

Frequently Asked Questions

What is an HTML Validator?

An HTML validator is a tool that checks your markup to make sure it follows the standard rules of the HTML language. It acts like a proofreader for your code, catching things like unclosed tags, missing attributes, or improper nesting, which helps ensure your website is built correctly.

Why should I validate my HTML?

Validating your HTML is a crucial step because it helps guarantee that your webpages will look and work the same way across all browsers, like Chrome, Firefox, and Safari. Clean, valid code is also better for SEO, as it makes it easier for search engines to understand your content. It also makes your code easier to manage in the long run.

Is this the Same as the Official W3C Validator?

This tool is based on the same rules and standards set by the W3C (World Wide Web Consortium), but it’s not the official validator. We built it to be a fast and easy-to-use alternative that runs right in your browser. It checks for the most common and important issues to help you write high-quality code that aligns with best practices.

Can this Tool Check for Accessibility Issues?

Yes, it can help. While it is not a full accessibility checker, it does flag common HTML errors that hurt accessibility. For example, it will warn you if you forget to add an `alt` attribute to your images, which is essential for screen readers used by visually impaired users.

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