diff --git a/21.md b/21.md
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+++ b/21.md
@@ -0,0 +1,20 @@
+NIP-21
+======
+
+`nostr:` URL scheme
+-------------------
+
+`draft` `optional` `author:fiatjaf`
+
+This NIP standardizes the usage of a common URL scheme for maximum interoperability and openness in the network.
+
+The scheme is `nostr:`.
+
+The identifiers that come after are expected to be the same as those defined in NIP-19 (except `nsec`).
+
+## Examples
+
+- `nostr:npub1sn0wdenkukak0d9dfczzeacvhkrgz92ak56egt7vdgzn8pv2wfqqhrjdv9`
+- `nostr:nprofile1qqsrhuxx8l9ex335q7he0f09aej04zpazpl0ne2cgukyawd24mayt8gpp4mhxue69uhhytnc9e3k7mgpz4mhxue69uhkg6nzv9ejuumpv34kytnrdaksjlyr9p`
+- `nostr:note1fntxtkcy9pjwucqwa9mddn7v03wwwsu9j330jj350nvhpky2tuaspk6nqc`
+- `nostr:nevent1qqstna2yrezu5wghjvswqqculvvwxsrcvu7uc0f78gan4xqhvz49d9spr3mhxue69uhkummnw3ez6un9d3shjtn4de6x2argwghx6egpr4mhxue69uhkummnw3ez6ur4vgh8wetvd3hhyer9wghxuet5nxnepm`
diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@ NIPs stand for **Nostr Implementation Possibilities**. They exist to document wh
 - [NIP-16: Event Treatment](16.md)
 - [NIP-19: bech32-encoded entities](19.md)
 - [NIP-20: Command Results](20.md)
+- [NIP-21: `nostr:` URL scheme](21.md)
 - [NIP-22: Event created_at Limits](22.md)
 - [NIP-25: Reactions](25.md)
 - [NIP-26: Delegated Event Signing](26.md)