What is it?
The HTML Checker finds mistakes in web page code that can break how a page looks or works. Paste your HTML and it lists each problem with the line where it starts, such as tags that are never closed, wrongly nested tags, duplicate ids, images without alt text and missing page basics like the title.
Who is it for?
Bloggers editing a Blogger or WordPress template, students learning HTML, and anyone whose page layout suddenly “falls apart” after an edit and who cannot see why.
How to use it
- Paste your code into the HTML to check box, or tap Try a sample to see how it works.
- The list of problems updates as you type: ✕ marks an error, ! a warning. The line above it sums up, for example “2 errors, 1 warning. Tap Show to jump to the line.”
- Tap Show next to a problem to jump to that line, fix it, and watch the list update. Problems that are not on one line say Whole file. Clear empties the box.
Worked example
Paste <div><p>Hi</div>. The <p> closes itself here because HTML allows its end tag to be left out, so it is not reported. Now paste <div><span>Hi</div>: the checker reports that <span> is still open when </div> arrives, with the line it was opened on. Add </span> before </div> and the list clears.
Tips
- Tags like <br>, <img> and <meta> never need closing, and the checker knows it.
- For a big site, use the W3C validator as a final check; it also checks every attribute value.
Is my code uploaded?
No. The checker is downloaded once from a public download server (jsDelivr or cdnjs) and then runs inside your browser. Your code never leaves your device, so it is safe for work and client projects.
Errors and how to fix them
- “✓ No problems found”: the structure is fine. If the page still looks wrong, the cause is probably in the CSS: try the CSS Checker.
- Many errors after one line: one unclosed tag pushes every later tag out of place. Fix the first error, and most of the others usually disappear.
- Duplicate id: an id must be used only once per page, or labels, links and scripts point at the wrong element. Rename one of them.
- Image without alt text: add alt="a short description", or alt="" for a purely decorative picture.
- Template tags reported: Blogger tags such as <b:if> are read as normal tags, so each must be closed (</b:if>) as well.
Open the tool: HTML Checker
Still stuck?
Contact support. Tell us which tool or page you were using, what you tapped, what you saw, and your phone or computer and browser (for example: Android phone, Chrome). We reply by email.
Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.