Check for duplicate 'id' values in a HTML page

The W3C's validator tool will report duplicate IDs. To test your code:

  1. Copy the generated source code to your clipboard.
  2. Visit
  3. Paste your markup into the box and hit 'Check'.

You can test it with the following code if you wish:

<!doctype html>
        <div id="test">Test div</div>
        <div id="test">Test div 2</div>

This produces the following error:

enter image description here


  2. If you have Web Developer Toolbar installed, you can use it to contact the above service directly from browser: Tools -> Validate Local HTML

  3. Some developer tools (like PhpStorm/WebStorm) automatically perform such validation.

Run this code on your browser’s JavaScript console:-

(function findDuplicateIds() {
    var ids = {};
    var all = document.all || document.getElementsByTagName("*");
    for (var i = 0, l = all.length; i < l; i++) {
        var id = all[i].id;
        if (id) {
            if (ids[id]) {
                console.log("Duplicate id: #" + id);
            } else {
                ids[id] = 1;