A table row was X columns wide and exceeded the column count established using column markup (Y).

A row in this table has more cells than its <colgroup> and <col> elements declare, so some of its cells sit past the last column the markup defines.

When a table has column markup, that markup sets the column count before any row is read. Each <col> adds one column, or as many as its span attribute says. A <colgroup> with no <col> inside adds the number in its own span, which defaults to 1. A row is X columns wide when its cells add up to X, with each cell counting as many columns as its colspan. The validator reports this error once for every row wider than the Y columns the markup declares.

A common cause is an empty <colgroup></colgroup> that a table editor or template writes into every table. It still counts as one column, so every row of a table with two or more columns triggers the error. Another cause is a column added to the rows but not to the <colgroup>. Browsers still show the extra cells, but styles set on <col>, such as width or background-color, don't reach the columns the markup leaves out.

To fix it, declare every column the rows use: add the missing <col> elements, raise the span, or remove a <colgroup> that doesn't style anything.

Invalid example

The <colgroup> declares one column, but each row has two cells:

<table>
  <colgroup>
    <col class="item">
  </colgroup>
  <tr>
    <th>Item</th>
    <th>Price</th>
  </tr>
  <tr>
    <td>Coffee</td>
    <td>2.50</td>
  </tr>
</table>

Valid example

One <col> for each column in the rows:

<table>
  <colgroup>
    <col class="item">
    <col class="price">
  </colgroup>
  <tr>
    <th>Item</th>
    <th>Price</th>
  </tr>
  <tr>
    <td>Coffee</td>
    <td>2.50</td>
  </tr>
</table>

Learn more:

MDN Reference

MDN Web Docs: The col element

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MDN Reference

MDN Web Docs: The colgroup element

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WHATWG Spec

HTML Standard: Tabular data

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