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無料 Webアプリマニフェストバリデーター

W3C仕様に基づいてWebアプリマニフェストJSONを検証し、インストール可能性チェックリストを表示します。

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Webアプリマニフェストバリデーターとは

A web app manifest is a JSON file that tells browsers how your web app should behave when installed on a user's device. It specifies the app name, icons, start URL, display mode, theme colors, and other properties. The manifest is linked from your HTML head with a link tag: <link rel="manifest" href="/site.webmanifest">.

クイックアンサー

Validate your web app manifest JSON for PWA installability. Required: name, icons (192x192 and 512x512), start_url, display mode (standalone/fullscreen/minimal-ui). The manifest must be linked in the HTML head and served with Content-Type: application/manifest+json.

制限事項

  • This validator checks the manifest JSON content only. It does not verify that icon files exist, that the start_url returns 200, or that the service worker is registered and functional.
  • The W3C Web App Manifest specification is evolving. New fields like protocol_handlers, shortcuts, and related_applications are not yet validated — check the latest spec for recently added fields.
  • Different browsers have different installability requirements. Chrome, Edge, Safari, and Firefox each interpret manifest fields slightly differently. Test on real devices across platforms.

使い方

  1. Paste the full JSON content of your web app manifest into the text area.
  2. The tool parses the JSON and checks each field against the W3C Web App Manifest specification.
  3. Review errors (must fix) and warnings (should fix) and follow the installability checklist before deploying.

主な用途

  • Validate a manifest before deploying a PWA to ensure installability requirements are met.
  • Debug why a PWA install prompt is not appearing — check the manifest fields that Chrome and Edge require.
  • Audit an existing manifest after adding new icons, changing the start URL, or updating theme colors.

用途

使用例

例

Pre-launch manifest check

A developer generates a manifest with the site's manifest generator and pastes it into the validator. The validator flags a missing short_name, suggests adding a 512x512 icon, and warns that the start_url does not start with /.

例

Debugging PWA install prompt

A PWA is not showing the install prompt on Chrome. Paste the manifest into the validator. It reports that the icons array is empty — without at least a 192x192 icon, Chrome does not offer the install prompt.

よくあるミス

  • Forgetting to link the manifest in the HTML head — the browser cannot discover the manifest without the link tag.
  • Using an empty or missing icons array — at minimum, a 192x192 and 512x512 PNG icon are required for the install prompt.
  • Setting the display mode to browser but expecting an installable app — standalone, fullscreen, or minimal-ui are the installable display modes.

検証

  1. Run a Lighthouse PWA audit — it checks the manifest along with other installability requirements.
  2. Open Chrome DevTools > Application > Manifest and verify all fields are parsed correctly and no errors are shown.

FAQ

WebアプリマニフェストバリデーターのFAQ

Why is my PWA install prompt not showing?

Chrome and Edge require: the manifest linked in the HTML head, served with the correct MIME type, containing at least name, short_name (or name < 30 chars), a 192x192 and 512x512 PNG icon, start_url within the scope, display set to standalone/fullscreen/minimal-ui, and a registered service worker. The site must also be served over HTTPS.

Is short_name required if name is already short?

If name is 30 characters or fewer, some platforms use it as the short name. However, explicitly setting short_name ensures consistent behavior across platforms. The recommended maximum for short_name is 12 characters — longer names are truncated on Android and iOS home screens.

What MIME type should the manifest be served with?

The manifest must be served with Content-Type: application/manifest+json. GitHub Pages serves .webmanifest files with this MIME type automatically. Netlify and Vercel also handle it correctly. If using a .json extension, you may need to configure your server to serve the correct MIME type.

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