diff --git a/CHANGELOG.md b/CHANGELOG.md
index fd0007c..b33ddb6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [v4.0.0] - Unreleased
+
+- [possum/at_uri] `collection` field now stores a parsed NSID
+- [possum/at_uri] `collection` and `rkey` now return a `Result(value, Nil)` since
+  fields might not be present.
+
 ## [v3.0.0] - 2026-07-13
 
 ### Added
diff --git a/src/possum/at_uri.gleam b/src/possum/at_uri.gleam
index 604bedf..158c305 100644
--- a/src/possum/at_uri.gleam
+++ b/src/possum/at_uri.gleam
@@ -1,7 +1,9 @@
+import gleam/option
 import gleam/result
 import gleam/string
 import possum/did
 import possum/handle
+import possum/nsid
 
 pub type ParseError {
   /// Only "at://" is supported
@@ -14,6 +16,8 @@ pub type ParseError {
   InvalidDidAuthority(reason: did.ParseError)
   /// Authority is an empty string
   MissingAuthority
+  /// Collection is not a valid NSID
+  InvalidCollection(reason: nsid.ParseError)
 }
 
 pub type Authority {
@@ -49,9 +53,9 @@ pub opaque type AtUri {
     /// Identifier, can be a DID or a Handle
     authority: Authority,
     /// Path
-    collection: String,
+    collection: option.Option(nsid.Nsid),
     /// Query string
-    rkey: String,
+    rkey: option.Option(String),
   )
 }
 
@@ -83,12 +87,15 @@ pub fn authority(self: AtUri) -> Authority {
 /// let string = "at://did:plc:vwzwgnygau7ed7b7wt5ux7y2/app.bsky.feed.post/3k5nobkf2w72g"
 /// let assert Ok(at_uri) = at_uri.parse(string)
 ///
-/// assert at_uri.collection(at_uri) == "app.bsky.feed.post"
+/// assert at_uri.collection(at_uri) == Ok("app.bsky.feed.post")
 /// ```
 ///
 /// See also: [Aturi](#AtUri)
-pub fn collection(self: AtUri) -> String {
-  self.collection
+pub fn collection(self: AtUri) -> Result(nsid.Nsid, Nil) {
+  case self.collection {
+    option.Some(nsid) -> Ok(nsid)
+    option.None -> Error(Nil)
+  }
 }
 
 /// Return the rkey part of the Uri
@@ -101,12 +108,15 @@ pub fn collection(self: AtUri) -> String {
 /// let string = "at://did:plc:vwzwgnygau7ed7b7wt5ux7y2/app.bsky.feed.post/3k5nobkf2w72g"
 /// let assert Ok(at_uri) = at_uri.parse(string)
 ///
-/// assert at_uri.rkey(at_uri) == "3k5nobkf2w72g"
+/// assert at_uri.rkey(at_uri) == Ok("3k5nobkf2w72g")
 /// ```
 ///
 /// See also: [Aturi](#AtUri)
-pub fn rkey(self: AtUri) -> String {
-  self.rkey
+pub fn rkey(self: AtUri) -> Result(String, Nil) {
+  case self.rkey {
+    option.Some(rkey) -> Ok(rkey)
+    option.None -> Error(Nil)
+  }
 }
 
 /// Parse a String into a valid At-Uri type
@@ -145,27 +155,39 @@ pub fn parse(content: String) -> Result(AtUri, ParseError) {
     //          ^^ authority
     [authority] -> {
       use authority <- result.map(parse_authority(authority))
-      AtUri(authority:, collection: "", rkey: "")
+      AtUri(authority:, collection: option.None, rkey: option.None)
     }
 
     // Contains at least authority and collection
     // ex: at://did:plc:vwzwgnygau7ed7b7wt5ux7y2/app.bsky.feed.post
     //          ^^ authority                     ^^ collection
     [authority, collection] -> {
-      use authority <- result.map(parse_authority(authority))
-      AtUri(authority:, collection:, rkey: "")
+      use authority <- result.try(parse_authority(authority))
+      use collection <- result.map(parse_collection(collection))
+      AtUri(authority:, collection: option.Some(collection), rkey: option.None)
     }
 
     // Contains authority, collection and rkey
     // ex: at://did:plc:vwzwgnygau7ed7b7wt5ux7y2/app.bsky.feed.post/3k5nobkf2w72g
     //          ^^ authority                     ^^ collection      ^^ rkey
     [authority, collection, rkey, ..] -> {
-      use authority <- result.map(parse_authority(authority))
-      AtUri(authority:, collection:, rkey:)
+      use authority <- result.try(parse_authority(authority))
+      use collection <- result.map(parse_collection(collection))
+
+      AtUri(
+        authority:,
+        collection: option.Some(collection),
+        rkey: option.Some(rkey),
+      )
     }
   }
 }
 
+fn parse_collection(collection: String) -> Result(nsid.Nsid, ParseError) {
+  nsid.parse(collection)
+  |> result.map_error(InvalidCollection)
+}
+
 fn parse_authority(string: String) -> Result(Authority, ParseError) {
   case string {
     "did:" <> _rest ->
@@ -204,9 +226,15 @@ pub fn to_string(self: AtUri) -> String {
   }
 
   let path = case self.collection, self.rkey {
-    "", _ -> ""
-    collection, "" -> "/" <> collection
-    collection, rkey -> "/" <> collection <> "/" <> rkey
+    // Authority only
+    option.None, _ -> ""
+
+    // Authority and collection
+    option.Some(nsid), option.None -> "/" <> nsid.to_string(nsid)
+
+    // Authority, collection and rkey
+    option.Some(nsid), option.Some(rkey) ->
+      "/" <> nsid.to_string(nsid) <> "/" <> rkey
   }
 
   "at://" <> host <> path