A table row was X columns wide, which is less than the column count established using column markup (Y).

A row in this table has fewer cells than its <colgroup> and <col> elements declare, so the row ends before the last column the markup defines.

Column markup sets the column count before any row is read. Each <col> adds one column, or as many as its span attribute says, and a <colgroup> with no <col> inside adds the number in its own span. A row is X columns wide when its cells add up to X, counting each cell's colspan and any cell from a row above that reaches down with rowspan. The validator reports this error once for every row narrower than the Y columns the markup declares. When no row reaches column Y at all, it also reports that table column Y established by element col (or colgroup) has no cells beginning in it.

A common cause is a column deleted from the rows while its <col> stays in the <colgroup>, for example after removing a column in a visual table editor. Without column markup, a short row only gets a warning. With it, the validator reports an error.

To fix it, make the column markup and the rows agree. If the column is gone, remove its <col> or lower the span. If the column should stay, add the missing cells to each short row, with an empty <td></td> where there is no data. A colspan on the last cell of a short row also clears this error, but when no row has a cell that starts in the last column, the validator then reports that column as having no cells.

Invalid example

The <colgroup> declares four columns, but each row has three cells:

<table>
  <colgroup>
    <col class="item">
    <col class="size">
    <col class="price">
    <col class="stock">
  </colgroup>
  <tr>
    <th>Item</th>
    <th>Size</th>
    <th>Price</th>
  </tr>
  <tr>
    <td>T-shirt</td>
    <td>M</td>
    <td>15.00</td>
  </tr>
</table>

Valid example

The <col> for the removed column is gone, so the markup declares three columns:

<table>
  <colgroup>
    <col class="item">
    <col class="size">
    <col class="price">
  </colgroup>
  <tr>
    <th>Item</th>
    <th>Size</th>
    <th>Price</th>
  </tr>
  <tr>
    <td>T-shirt</td>
    <td>M</td>
    <td>15.00</td>
  </tr>
</table>

Learn more:

MDN Reference

MDN Web Docs: The col element

→

MDN Reference

MDN Web Docs: The colgroup element

→

WHATWG Spec

HTML Standard: Tabular data

→