diff --git a/pylib/anki/tags.py b/pylib/anki/tags.py
index 2fd52375e..bb48e47c3 100644
--- a/pylib/anki/tags.py
+++ b/pylib/anki/tags.py
@@ -42,30 +42,14 @@ class TagManager:
     def register(
         self, tags: Collection[str], usn: Optional[int] = None, clear=False
     ) -> None:
-        if usn is None:
-            preserve_usn = False
-            usn_ = 0
-        else:
-            usn_ = usn
-            preserve_usn = True
-
-        self.col.backend.register_tags(
-            tags=" ".join(tags), preserve_usn=preserve_usn, usn=usn_, clear_first=clear
-        )
+        print("tags.register() is deprecated and no longer works")
 
     def registerNotes(self, nids: Optional[List[int]] = None) -> None:
-        "Add any missing tags from notes to the tags list."
-        # when called without an argument, the old list is cleared first.
-        if nids:
-            lim = " where id in " + ids2str(nids)
-            clear = False
-        else:
-            lim = ""
-            clear = True
-        self.register(
-            self.col.backend.get_note_tags(nids),
-            clear=clear,
-        )
+        "Clear unused tags and add any missing tags from notes to the tag list."
+        self.clear_unused_tags()
+
+    def clear_unused_tags(self):
+        self.col.backend.clear_unused_tags()
 
     def byDeck(self, did, children=False) -> List[str]:
         basequery = "select n.tags from cards c, notes n WHERE c.nid = n.id"
diff --git a/rslib/backend.proto b/rslib/backend.proto
index 974e9d759..1bfecfbce 100644
--- a/rslib/backend.proto
+++ b/rslib/backend.proto
@@ -165,7 +165,6 @@ service BackendService {
   rpc RemoveNotes(RemoveNotesIn) returns (Empty);
   rpc AddNoteTags(AddNoteTagsIn) returns (UInt32);
   rpc UpdateNoteTags(UpdateNoteTagsIn) returns (UInt32);
-  rpc GetNoteTags(GetNoteTagsIn) returns (GetNoteTagsOut);
   rpc ClozeNumbersInNote(Note) returns (ClozeNumbersInNoteOut);
   rpc AfterNoteUpdates(AfterNoteUpdatesIn) returns (Empty);
   rpc FieldNamesForNotes(FieldNamesForNotesIn) returns (FieldNamesForNotesOut);
@@ -208,10 +207,10 @@ service BackendService {
 
   // tags
 
-  rpc RegisterTags(RegisterTagsIn) returns (Bool);
+  rpc ClearUnusedTags(Empty) returns (Empty);
   rpc AllTags(Empty) returns (AllTagsOut);
-  rpc SetTagCollapsed(SetTagCollapsedIn) returns (Bool);
-  rpc ClearTag(String) returns (Bool);
+  rpc SetTagCollapsed(SetTagCollapsedIn) returns (Empty);
+  rpc ClearTag(String) returns (Empty);
   rpc TagTree(Empty) returns (TagTreeNode);
 
   // config/preferences
@@ -811,13 +810,6 @@ message AddOrUpdateDeckConfigLegacyIn {
   bool preserve_usn_and_mtime = 2;
 }
 
-message RegisterTagsIn {
-  string tags = 1;
-  bool preserve_usn = 2;
-  int32 usn = 3;
-  bool clear_first = 4;
-}
-
 message AllTagsOut {
   repeated Tag tags = 1;
 }
@@ -950,14 +942,6 @@ message UpdateNoteTagsIn {
   bool regex = 4;
 }
 
-message GetNoteTagsIn {
-  repeated int64 nids = 1;
-}
-
-message GetNoteTagsOut {
-  repeated string tags = 1;
-}
-
 message CheckDatabaseOut {
   repeated string problems = 1;
 }
diff --git a/rslib/src/backend/mod.rs b/rslib/src/backend/mod.rs
index 170f978f9..15863b5dc 100644
--- a/rslib/src/backend/mod.rs
+++ b/rslib/src/backend/mod.rs
@@ -44,6 +44,7 @@ use crate::{
         get_remote_sync_meta, sync_abort, sync_login, FullSyncProgress, NormalSyncProgress,
         SyncActionRequired, SyncAuth, SyncMeta, SyncOutput, SyncStage,
     },
+    tags::join_tags,
     template::RenderedNode,
     text::{escape_anki_wildcards, extract_av_tags, strip_av_tags, AVTag},
     timestamp::TimestampSecs,
@@ -974,14 +975,6 @@ impl BackendService for Backend {
         })
     }
 
-    fn get_note_tags(&self, input: pb::GetNoteTagsIn) -> BackendResult<pb::GetNoteTagsOut> {
-        self.with_col(|col| {
-            Ok(pb::GetNoteTagsOut {
-                tags: col.storage.get_note_tags(to_nids(input.nids))?,
-            })
-        })
-    }
-
     fn cloze_numbers_in_note(&self, note: pb::Note) -> BackendResult<pb::ClozeNumbersInNoteOut> {
         let mut set = HashSet::with_capacity(4);
         for field in &note.fields {
@@ -1360,34 +1353,32 @@ impl BackendService for Backend {
         Ok(pb::AllTagsOut { tags })
     }
 
-    fn set_tag_collapsed(&self, input: pb::SetTagCollapsedIn) -> BackendResult<pb::Bool> {
+    fn set_tag_collapsed(&self, input: pb::SetTagCollapsedIn) -> BackendResult<pb::Empty> {
         self.with_col(|col| {
             col.transact(None, |col| {
                 col.set_tag_collapsed(&input.name, input.collapsed)?;
-                Ok(pb::Bool { val: true })
+                Ok(().into())
             })
         })
     }
 
-    fn register_tags(&self, input: pb::RegisterTagsIn) -> BackendResult<pb::Bool> {
+    fn clear_unused_tags(&self, _input: pb::Empty) -> BackendResult<pb::Empty> {
         self.with_col(|col| {
             col.transact(None, |col| {
-                let usn = if input.preserve_usn {
-                    Usn(input.usn)
-                } else {
-                    col.usn()?
-                };
-                col.register_tags(&input.tags, usn, input.clear_first)
-                    .map(|val| pb::Bool { val })
+                let old_tags = col.storage.all_tags()?;
+                let note_tags = join_tags(&col.storage.get_note_tags()?);
+                col.register_tags(&note_tags, col.usn()?, true)?;
+                col.update_tags_collapse(old_tags)?;
+                Ok(().into())
             })
         })
     }
 
-    fn clear_tag(&self, tag: pb::String) -> BackendResult<pb::Bool> {
+    fn clear_tag(&self, tag: pb::String) -> BackendResult<pb::Empty> {
         self.with_col(|col| {
             col.transact(None, |col| {
                 col.storage.clear_tag(tag.val.as_str())?;
-                Ok(pb::Bool { val: true })
+                Ok(().into())
             })
         })
     }
diff --git a/rslib/src/dbcheck.rs b/rslib/src/dbcheck.rs
index 80cccbc30..ac76b0147 100644
--- a/rslib/src/dbcheck.rs
+++ b/rslib/src/dbcheck.rs
@@ -295,17 +295,8 @@ impl Collection {
             }
         }
 
-        let new_tags = self.storage.all_tags_sorted()?;
-        for old in old_tags.into_iter() {
-            for new in new_tags.iter() {
-                if new.name == old.name {
-                    self.storage.set_tag_collapsed(&new.name, new.collapsed)?;
-                    break;
-                } else if new.name.starts_with(&old.name) {
-                    self.set_tag_collapsed(&old.name, old.collapsed)?;
-                }
-            }
-        }
+        // restore tags collapse state and re-register old tags that are parents of used ones
+        self.update_tags_collapse(old_tags)?;
 
         // if the collection is empty and the user has deleted all note types, ensure at least
         // one note type exists
diff --git a/rslib/src/storage/note/mod.rs b/rslib/src/storage/note/mod.rs
index e109d9f33..b2d582a93 100644
--- a/rslib/src/storage/note/mod.rs
+++ b/rslib/src/storage/note/mod.rs
@@ -158,17 +158,10 @@ impl super::SqliteStorage {
     }
 
     // get distinct note tags
-    pub(crate) fn get_note_tags(&self, nids: Vec<NoteID>) -> Result<Vec<String>> {
-        if nids.is_empty() {
-            self.db
-                .prepare_cached("select distinct tags from notes")?
-                .query_and_then(NO_PARAMS, |r| Ok(r.get_raw(0).as_str()?.to_owned()))?
-                .collect()
-        } else {
-            self.db
-                .prepare_cached("select distinct tags from notes where id in ?")?
-                .query_and_then(nids, |r| Ok(r.get_raw(0).as_str()?.to_owned()))?
-                .collect()
-        }
+    pub(crate) fn get_note_tags(&self) -> Result<Vec<String>> {
+        self.db
+            .prepare_cached("select distinct tags from notes")?
+            .query_and_then(NO_PARAMS, |r| Ok(r.get_raw(0).as_str()?.to_owned()))?
+            .collect()
     }
 }
diff --git a/rslib/src/tags.rs b/rslib/src/tags.rs
index 6de9d2031..f7c61ace4 100644
--- a/rslib/src/tags.rs
+++ b/rslib/src/tags.rs
@@ -272,6 +272,22 @@ impl Collection {
         self.storage.set_tag_collapsed(name, collapsed)
     }
 
+    /// Update collapse state of existing tags and register tags in old_tags that are parents of those tags
+    pub(crate) fn update_tags_collapse(&self, old_tags: Vec<Tag>) -> Result<()> {
+        let new_tags = self.storage.all_tags_sorted()?;
+        for old in old_tags.into_iter() {
+            for new in new_tags.iter() {
+                if new.name == old.name {
+                    self.storage.set_tag_collapsed(&new.name, old.collapsed)?;
+                    break;
+                } else if new.name.starts_with(&old.name) {
+                    self.set_tag_collapsed(&old.name, old.collapsed)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
     fn replace_tags_for_notes_inner<R: Replacer>(
         &mut self,
         nids: &[NoteID],