HTML Validator
Validate HTML markup
HTML Validator: Validate HTML markup. A free, browser-based tool from DevToolbox that runs entirely on your own device: no upload, no account, no tracking.
About the HTML Validator
Check HTML markup for the structural problems that break rendering (unclosed elements, mismatched tags, stray closers), plus a few accessibility basics like images without alternative text.
Formatting happens by parsing your input into a structure and printing it back out with consistent indentation, so the result is the same document with different whitespace, never a rewrite of its meaning. Invalid input is reported with the position that broke the parse rather than silently repaired.
What you can do with it
- HTML checker
- Validate HTML online
- HTML syntax checker
- HTML error checker
How to use it
- Paste or type your code into the input pane.
- The formatted result appears in the output pane as you type. There is no run button to press.
- If the input will not parse, the status bar turns red and names the problem and its position.
- Use Copy to put the formatted result on your clipboard.
Questions
- Is this the same as the W3C validator?
- No. The W3C service performs a full conformance check against the spec and needs a server to do it. This checks structure and common mistakes locally, which catches most real problems without sending your markup anywhere.
- Is my data uploaded anywhere?
- No. The tool is JavaScript that runs in the tab you already have open, and DevToolbox has no backend to send anything to. You can open the network tab and watch: after the page and its script load, nothing is sent while you work.
Related tools
The HTML Validator sits in Beautifiers & Formatters, one of the 90 tools on DevToolbox.