---
name: Screen reader
slug: screen-reader
description: Authoring helper for building Sprout canvases with read-aloud narration and word highlighting synced to browser speech boundary events.
category: home_agent
trustTier: experimental
kidCallable: false
status: published
pairs_with_patterns:
  - canvas
  - journal
pairs_with_nouns:
  - Canvas
  - Skill
handsReferenced:
  - canvas_create
  - canvas_update
inputVariables:
  - name: canvas_goal
    display_name: Canvas goal
    description: What the canvas is trying to teach or do.
    json_schema: { type: string }
  - name: narration_text
    display_name: Narration text
    description: The sentence or lesson text to read aloud and highlight.
    json_schema: { type: string }
---

# Skill prompt

When building or updating a Sprout canvas that reads text aloud, use this procedure.

Use browser SpeechSynthesisUtterance.onboundary with charIndex to highlight the actual word being spoken. Do not rely on guessed timers for word highlighting unless the selected browser voice does not emit boundary events.

Implementation pattern:
1. Tokenize the sentence with a regex that records each word's start and end character offsets.
2. Render each word as a span with data-start and data-end attributes.
3. On SpeechSynthesisUtterance.onboundary, read event.charIndex and mark the span whose character range contains that index.
4. Clear the active word on onend or onerror.
5. If no boundary events arrive, surface that limitation or use a conservative fallback; do not present the fallback as exact sync.

For lesson screens, make narration unskippable when requested: disable Next, Replay, and Play while narration is speaking, then unlock them only in the onend/onerror completion path. Replay should lock the page again until the replay narration completes.

Keep Sprout canvas constraints in mind: no external scripts, no fetch, no localStorage, and exactly one final sprout.score, sprout.complete, or sprout.timed completion call at the end of the activity. The reader helper itself must not call completion.