Input validation a11y

Input Validation Accessibility

Instructions

Validation is the most frequent reason a user hears silence from the screen reader while the UI lights up red. Make validation visible and audible, and make recovery obvious.

1. When to Validate

• On blur for per-field format errors (invalid email, bad phone).
• On submit for completeness ("Name required", "Accept terms required").
• Live as-you-type only for password strength meters and character counts — always additive, never blocking.

Avoid validating on every keystroke — the stream of announcements is unusable with VoiceOver / TalkBack.

2. Error Message Rules

• Say what is wrong and how to fix it: "Enter a valid email address, for example [email protected]".
• Avoid vague messages: "Invalid input", "Try again".
• Use the field label: "Email is required" (not "This field is required").
• Keep it short — screen readers read it verbatim.

3. Live Region Announcements

When an error appears, announce it automatically without stealing focus.

iOS (SwiftUI):

Text(error ?? "")
    .foregroundStyle(.red)
    .accessibilityHidden(error == nil)
    .onChange(of: error) { _, new in
        if let msg = new { UIAccessibility.post(notification: .announcement, argument: msg) }
    }

UIKit — set the error label's accessibility trait:

errorLabel.accessibilityTraits = .staticText
errorLabel.text = message
UIAccessibility.post(notification: .announcement, argument: message)

Compose:

if (error != null) {
    Text(
        text = error,
        color = MaterialTheme.colorScheme.error,
        modifier = Modifier.semantics { liveRegion = LiveRegionMode.Assertive }
    )
}

Flutter:

SemanticsService.announce('Email is required', Directionality.of(context));

RN:

<Text
  accessibilityRole="alert"
  accessibilityLiveRegion="assertive"
  style={styles.error}>{error}</Text>

Use polite for non-blocking warnings (password strength moving to "weak"), assertive for blocking errors only.

4. Associating Errors With Fields

Screen readers should read the error as part of the field.

UIKit:

emailField.accessibilityLabel = "Email"
emailField.accessibilityValue = email
emailField.accessibilityHint = error ?? ""

Better — use a combined label so the reader announces "Email, required. Error: must include @":

emailField.accessibilityLabel = "Email, required. \(error.map { "Error: \($0)" } ?? "")"

Compose:

OutlinedTextField(
    value = email,
    onValueChange = ::onChange,
    label = { Text("Email") },
    isError = error != null,
    supportingText = { if (error != null) Text(error) },
    modifier = Modifier.semantics {
        if (error != null) this.error(error)
    }
)

The error(...) semantics property tells TalkBack the field is invalid and reads the message.

Flutter — TextFormField already sets semantics when errorText is non-null.

RN:

<TextInput
  accessibilityLabel="Email"
  accessibilityInvalid={!!error}
  aria-errormessage="emailError" /* web */ />
<Text nativeID="emailError" accessibilityLiveRegion="polite">{error}</Text>

5. Error Summary on Submit

For long forms (signup, checkout), show a summary at the top on submit failure and move focus there, or to the first invalid field.

// SwiftUI
if !errors.isEmpty {
    VStack(alignment: .leading) {
        Text("Please fix the following:").font(.headline)
        ForEach(errors) { err in
            Button(err.message) { focus = err.field } // jump to field
        }
    }
    .accessibilityElement(children: .contain)
    .accessibilityAddTraits(.isHeader)
    .onAppear { announceScreenChange() }
}

Move focus to the summary heading so the reader picks it up.

6. Async / Server-Side Errors

• Network errors: "Couldn't sign in. Check your connection and try again." — actionable, no jargon.
• Server validation: map codes to human text, reuse the same a11y pattern (live region + field association).
• Don't lose the user's input on network failure.

7. Success States

Also announce success so AT users know the flow moved forward.

Snackbar(
    modifier = Modifier.semantics { liveRegion = LiveRegionMode.Polite }
) { Text("Profile saved") }

8. Password Strength Meters

• Announce strength changes via a polite live region only when the bucket changes (weak → medium → strong), not on every keystroke.
• Provide text alongside the visual bar (never bar-only).

9. Character Counters

For length-limited fields, expose the counter via accessibilityValue and update live as typing progresses — but throttle to announce every 10 characters or on pause, not every keystroke.

TextField(
  maxLength: 280,
  decoration: InputDecoration(counterText: '$length of 280'),
)

10. Common Pitfalls

• Red border only, no text.
• Error text present but not announced.
• Focus jumps to top on submit instead of to the summary or first error.
• Live region re-announces every keystroke.
• Error message contains the wrong field name.
• Success banner never announced; AT user doesn't know the save worked.
• Server error returns HTTP status code to the user ("Error 422").

Checklist

• Each error paired with an explanation and a recovery hint.
• Errors announced via live region (polite or assertive as appropriate).
• Field's a11y state set to invalid / error() while message is present.
• On submit failure, focus moves to summary or first invalid field.
• Success states announced politely.
• Character counters / password meters announce on bucket change, not per key.
• User's input preserved on network errors.