Techniques for WCAG 2.0

Skip to Content (Press Enter)


H93: Ensuring that id attributes are unique on a Web page


All HTML pages

This technique relates to:


The objective of this technique is to avoid key errors that are known to cause problems for assistive technologies when they are trying to parse content that has the same id attribute on different elements. These errors can be avoided by making sure the Web page does not have duplicate id values. This can be done manually or by using HTML's mechanism to specify the technology and technology version, and validating the document for this condition. There are several validators that the developer can use; validation reports generally mention this type of error. The document type declaration is not strictly necessary for this type of evaluation, but specifying the document type declaration makes it easier to use a validator.


Example 1: HTML Validators

HTML pages include a document type declaration (sometimes referred to as !DOCTYPE statement). The developer can use offline or online validators (see Resources below) to check that id attributes values are only used once on a page. The W3C validador, for example, will report ID "X already defined" when it encounters the second use of an id value.


Resources are for information purposes only, no endorsement implied.

For other resources, see G134: Validating Web pages.



  1. Check that all id attribute values are unique on the web page.

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.