What is an accessible error message for a form field?

Answer

Put a concise, actionable message near the field, programmatically associate it with the input, and move focus or announce a summary after submission when appropriate. Explain how to fix the issue, not only that validation failed.

Context

Accessible interfaces use semantic HTML, predictable keyboard behavior, visible focus, and clear feedback. Build those requirements into the component contract from the start.

Example

<button type="button" aria-expanded="false" aria-controls="filters">
  Show filters
</button>
<section id="filters" hidden>…</section>

The native button supplies keyboard behavior; aria-expanded communicates the visible state.

Practical considerations

1. Choose the approach from the requirement and constraints, not from habit.
2. Include validation, error handling, and cleanup where the boundary requires them.
3. Verify the observable result with focused tests or measurement.

Follow-up prompts

• What failure mode would you expect if this were implemented incorrectly?
• How would you test this behaviour?
• What changes when the feature must scale to a larger application or team?

In practice

For this medium-level topic, make assumptions explicit, choose the smallest safe implementation, and verify the behavior at the relevant boundary.