diff --git a/src/at/nsid.gleam b/src/at/nsid.gleam
index 8796076..dc4e4f9 100644
--- a/src/at/nsid.gleam
+++ b/src/at/nsid.gleam
@@ -340,6 +340,17 @@ pub fn name(nsid: Nsid) -> String {
   nsid.name
 }
 
+/// Construct a domain name from an [`Nsid`](#Nsid) authority. This reverses the
+/// authority segments back into the order they would appear in a typical domain
+/// name, such as `"bsky.app"` or `"atproto.com"`.
+/// 
+pub fn domain(nsid: Nsid) -> String {
+  let assert [tld, ..rest] = nsid.authority
+  use out, segment <- list.fold(rest, tld)
+
+  segment <> "." <> out
+}
+
 // CONVERSIONS -----------------------------------------------------------------
 
 /// Convert an [`Nsid`](#Nsid) back into its string representation.