Why it matters

client:only skips server rendering, and server:defer renders later on demand. Fallback content gives users immediate context instead of leaving an empty region while the island loads.

See the difference

Incorrect

Island with no fallback

---
import Chart from '../components/Chart.tsx'
---
<Chart client:only="react" />

Correct

Island with fallback content

---
import Chart from '../components/Chart.tsx'
---
<Chart client:only="react">
  <div slot="fallback">Loading chart...</div>
</Chart>

Configure this check

Override the default severity in your ESLint config:

import astroDoctorPlugin from '@santi020k/eslint-plugin-astro-doctor'

export default [
  astroDoctorPlugin.configs.recommended,
  {
    rules: {
      'astro-doctor/require-island-fallback': 'error',
    },
  },
]

Or set the severity for CLI scans in doctor.config.ts:

export default {
  rules: {
    'astro-doctor/require-island-fallback': 'error',
  },
}

Use 'error', 'warn', or 'off'. The configuration guide covers presets and per-file overrides.

Keep exploring accessibility

Browse every rule and project audit