Free Online HTML Validator

Most broken pages are broken in boring ways. A <div> that never closes, so everything after it sits inside the wrong box. Two elements with the same id, so a script or a stylesheet finds only the first. An image with an empty src, or no alt text. An attribute wrapped in single quotes. This HTML validator runs a fixed set of checks for exactly those mistakes and shows each one with its line and column, so you can check HTML in seconds instead of scanning it by eye.

Who It Is For

Anyone holding HTML they did not write from scratch. If ChatGPT or Claude produced a landing page for you, a designer handed over a template, or a course gave you a starter file, you probably cannot tell by looking whether the markup is sound. Paste it here and you will know. Developers use an HTML checker before a code review or a deploy; writers and marketers use one when a page “looks off” and they want to validate HTML before blaming the CSS.

How It Works

The checking runs entirely in your browser using HTMLHint, an open-source HTML syntax checker, loaded on demand the first time you paste. Nothing is sent to a server while you validate. The list updates as you type; the filter at the top switches between all problems, errors only and warnings only; and clicking a row selects the offending line in the editor and scrolls to it. The rules that are on are the ones that catch real breakage: unpaired tags, uppercase tag and attribute names, single-quoted or duplicated attributes, duplicate ids, a missing doctype or title, a missing alt, an empty src, and bare < or > characters in text. The rules that are off are the opinionated ones: inline styles, scripts in the head and mixed spaces and tabs are never flagged, and neither are framework attributes like x-data or hx-get.

What It Does Not Do

This is a fast linter, not a W3C validator alternative in the strict sense: it does not check every rule of the HTML specification, and a clean result here means the common mistakes are gone, not that the page is fully conformant. It also does not rewrite anything. To tidy the indentation once the errors are fixed, use the HTML formatter; to see the page actually render, paste it into the HTML tester.

Then Put It On A Link

Once the list says no problems found, the natural next step is to see the page live. The publish button below the validator puts your HTML on a free OxyPages subdomain with HTTPS, in seconds, with no account. The link lasts 30 minutes; claiming it is free and keeps it permanently, with your own address and, on paid plans, a custom domain. Instant publishing accepts pages up to 5 MB. Read how it works or compare plans.