Techniques for WCAG 2.0

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H45: Using longdesc


HTML and XHTML documents that include images that cannot be described in a short text alternative.

This technique relates to:

User Agent and Assistive Technology Support Notes

User Agent support for longdesc varies, but overall support is improving. Screen readers such as JAWS, NVDA, and Window-Eyes support longdesc, but Voiceover 4.0, Orca 2.32.0, and screen magnifier Zoomtext 10.0 do not yet support the longdesc attribute. Browsers including Internet Explorer, Firefox, Opera, and Chrome (planned) all support longdesc.


The objective of this technique is to provide information in a file designated by the longdesc attribute when a short text alternative does not adequately convey the function or information provided in the image. The longdesc attribute is a URI, the target of which contains a long description of the non-text content.

Authors can provide a description for an image by including text in a separate resource or within the text of the page containing the image. An advantage of providing the description within the same page as the image is that all users can access the description. A limitation of this method, as well as in providing multiple descriptions on a single separate page, is that current implementations supporting longdesc read all text on the page that follows the start of the long description. As a result, an end user may hear the long description and all content on the page following it, without knowing where the long description is intended to end unless authors provide text to help users identify the end-point of the description.


Example 1: Using longdesc to refer to a long description contained on a separate resource.

Example Code:

<p><img src="chart.gif" alt="a complex chart" longdesc="chartdesc.html"/></p>

Example 2: Using longdesc to refer to a long description within the same page.

Example Code:

<img longdesc="thispage.html#desc" alt="Line graph of the number of subscribers" src="">
<div id="desc">
 <!-- Full Description of Graph -->



  1. Check that the img element has a longdesc attribute.

  2. Check that the value of the longdesc attribute is a valid URI of an existing resource.

  3. Check that the content at the target of that URI contains a long description describing the original non-text content associated with it.

Expected Results

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.

Techniques are Informative

Techniques are informative—that means they are not required. The basis for determining conformance to WCAG 2.0 is the success criteria from the WCAG 2.0 standard—not the techniques. For important information about techniques, please see the Understanding Techniques for WCAG Success Criteria section of Understanding WCAG 2.0.