Definition
Plain language
A structured map of what's on a screen that assistive tools and AI agents read instead of looking at pixels.
As stated in the literature
A semantic tree representation of UI elements exposed by an operating system or browser for screen readers and automation, used by computer-use agents as a non-pixel input channel.
Why it matters: It lets AI agents reliably read web pages and apps without the fragility of pixel-level vision, and gives blind users access to the same software.
For example, a screen reader uses the accessibility tree to announce 'Submit button' instead of describing a blob of pixels.
Heard on the show
“An accessibility tree reader.”Episode 062 — Treating Hallucinations as Exploits: A Gate-Based Architecture for Agent Safety