ERR_UNKNOWN_URL_SCHEME, what it means and how to fix it

Every address starts with a scheme (https:, http:, mailto:) that tells the browser what protocol to speak. This error means the scheme is one Chrome does not know how to open: usually a custom scheme belonging to an app (intent://, a banking or conferencing app's private scheme), a web+ handler nobody registered, or a malformed link where the scheme is misspelled or mangled.

The fix, in order

  1. Check the start of the address. A typo'd or doubled scheme (httpshttps://, htp://) or a link copied with extra characters produces this instantly. Correct it to https:// and retry.
  2. If the link was supposed to open an app, open the app directly. Custom schemes only work when the app that owns them is installed and registered. If the app is missing or was updated and dropped its registration, reinstalling or updating it restores the handoff.
  3. On Android, check the app link defaults. Links that should open an app but land in Chrome with this error usually mean the app lost its “open supported links” permission; re-enable it in the app's Android settings.
  4. If you are the developer, register the scheme or protocol handler correctly, and prefer universal links (https URLs the app claims) over custom schemes; custom schemes fail exactly like this whenever the app is absent, which is why the platform guidance moved away from them.

If it still happens

A scheme error that appears for one specific link, everywhere, means the link itself is built wrong (the site's markup names a handler that does not exist). Report it to the site; no visitor setting can register a protocol on a website's behalf.

Common questions

Is ERR_UNKNOWN_URL_SCHEME dangerous? Not by itself; it means the browser declined to open something it does not understand. Treat unexpected scheme links in emails and messages with the usual suspicion, since custom schemes can invoke apps, but the error itself is the browser refusing, which is the safe outcome.

What is the difference between this and a 404? A 404 means the browser successfully spoke HTTP to a server that said the page is not there. An unknown scheme error happens before any server contact: the browser cannot even begin, because it does not know the protocol the address names.

Related errors

ERR_UNSAFE_PORT · ERR_INVALID_RESPONSE · ERR_BLOCKED_BY_RESPONSE