What happens when an aria-describedby points at a missing ID?

Nothing visible, which is the danger. The browser cannot resolve the reference, so the accessibility tree simply has no description for that element. A screen reader user hears the name and role but no help text, and there is no error or warning to alert the developer.

What is the difference between aria-describedby and aria-labelledby?

aria-labelledby supplies the element's accessible name (what is announced as its label), while aria-describedby supplies an additional description announced after the name, such as a hint or error message. Both take a space-separated list of element IDs and both fail silently if an ID is missing.

Does the order of multiple IDs matter?

Yes. Both attributes accept several IDs separated by spaces, and the referenced text is concatenated in the order listed. If one ID in the list is missing it is skipped, so a partial reference can produce a confusingly incomplete description.

Why does a duplicate ID matter here?

ID references resolve to the first element with that ID. If two elements share an ID, the reference may resolve to the wrong one, giving the wrong description. This tool also flags duplicate IDs because they make ARIA references unreliable even when they technically resolve.

Is my HTML sent anywhere?

No. Parsing and validation run entirely in your browser using its built-in HTML parser. Nothing you paste is uploaded.

aria-describedby & aria-details Validator

ARIA attributes like aria-describedby and aria-labelledby wire an element to other elements by ID. If the target ID does not exist, the reference fails silently: there is no console error, no visual change, just a missing description that a screen reader user never hears. This validator scans your markup and reports every broken reference so you can catch them before they ship.

How it works

The tool parses your pasted HTML with the browser’s own parser, then walks every element carrying an ID-referencing ARIA attribute:

aria-describedby — additional description announced after the name
aria-labelledby — the accessible name itself
aria-details — a reference to richer, structured details
aria-controls, aria-owns, aria-flowto, aria-activedescendant, aria-errormessage — other IDREF/IDREF-list attributes that fail the same way

Each attribute value is split on whitespace into individual IDs (these attributes take a space-separated IDREF list). For every ID the tool checks whether an element with that exact id exists in the parsed document. A reference is resolved if every ID it lists is found, and broken if any ID is missing. The validator also collects all id values and flags duplicates, because a reference that resolves to the wrong duplicate is just as buggy as one that resolves to nothing.

Example

Given:

<input aria-describedby="hint err" id="email" />
<span id="hint">We never share your email.</span>

The reference lists two IDs, hint and err. hint resolves, but there is no element with id="err", so the validator reports a broken reference on the input pointing at the missing err. A screen reader would announce only the hint, silently dropping the intended error description.

Tips and notes

A broken reference produces no runtime error, so it survives manual testing easily — automated checks like this one are the reliable way to catch it.
Keep error-message elements in the DOM (visually hidden if needed) so that aria-describedby and aria-errormessage always resolve, rather than adding and removing them.
Avoid duplicate IDs entirely; they break ARIA references and violate WCAG 4.1.1.
All processing is local to your browser; nothing you paste leaves the page.