Web app manifest id: a stable PWA identity

In one line: id is the string that identifies your web application. Because it is separate from start_url, you can later change where the app launches without the browser treating it as a different app.

Why id exists

Historically there was no single defined way to identify an installed web app: some browsers derived the identity from start_url, while others used the manifest file’s path. That made the launch URL effectively double as the identity, so changing start_url could cause a browser to treat the manifest as describing a different app and create a duplicate install instead of updating the existing one.

The id member standardizes this. It provides an explicit identity that is independent of start_url, so the launch URL and the durable identity are no longer the same value.

How id is resolved

• id is a string processed as a URL relative to the origin of start_url. So "id": "/?source=pwa" for an app whose start_url is on https://example.com resolves to https://example.com/?source=pwa.
• The resolved value becomes the application’s identity, which the browser uses to decide whether a manifest describes a previously-processed app.
• If id is omitted or cannot be parsed, the identity defaults to start_url. That default is what couples identity to the launch URL.
• Because id is resolved against the origin of start_url, it can only identify an app within that same origin; it cannot point at another site.

What to set it to

• Set id from the first release. Because an omitted id defaults to start_url, adding or changing id later can change the computed identity, so choosing it before anyone installs avoids disturbing existing installs.
• Keep it short and stable. Common choices are "id": "/" or a marker such as "id": "/?homescreen=1". The exact value does not matter as long as it never changes.
• Treat id as permanent. Changing it changes the app’s identity, which is the situation id exists to avoid.

{
  "name": "OpenPWA Demo",
  "start_url": "/app/?utm_source=pwa",
  "id": "/?homescreen=1",
  "display": "standalone"
}

In this manifest the app launches at /app/?utm_source=pwa, but its identity is the fixed /?homescreen=1. You can later move the launch path without changing the identity.

Browser & ecosystem support

The id member is defined in the Web App Manifest specification. Chrome added support for it in Chrome 96. Browsers that do not process id keep their existing identity behavior, so declaring id does not break anything where it is unsupported.

Practical checklist

• Add an id to your manifest before your first public install.
• Choose a short, permanent value (/ or a fixed marker query) and document it.
• Keep id stable so you can change the launch URL (start_url) independently.
• Avoid changing id after launch — it changes the app’s identity.
• Remember id resolves against the origin of start_url, so a leading / is enough.
• Verify in Chromium DevTools → Application → Manifest that the computed app id matches what you intended.