diff --git a/bluesky/input.py b/bluesky/input.py
index 164eae7..4264ef8 100644
--- a/bluesky/input.py
+++ b/bluesky/input.py
@@ -20,6 +20,7 @@ from cross.attachments import (
     MediaAttachment,
     QuoteAttachment,
     RemoteUrlAttachment,
+    TagsAttachment,
 )
 from cross.media import Blob, cleanup_blobs, download_blob
 from cross.post import Post, PostRef
@@ -187,6 +188,8 @@ class BlueskyBaseInputService(BlueskyService, InputService, ABC):
                     ]
                 ),
             )
+        if "tags" in record:
+            post.attachments.put(TagsAttachment(tags=record["tags"]))
 
         if parent:
             self._insert_post(
diff --git a/cross/attachments.py b/cross/attachments.py
index 902ef1a..c2358fd 100644
--- a/cross/attachments.py
+++ b/cross/attachments.py
@@ -8,39 +8,52 @@ class Attachment:
     pass
 
 
+# self labels, like CWs, or adult content labels
 @dataclass(kw_only=True)
 class LabelsAttachment(Attachment):
     labels: list[str]
 
 
+# languages used in the post
 @dataclass(kw_only=True)
 class LanguagesAttachment(Attachment):
     langs: list[str]
 
 
+# if media on this post is considered sensitive
 @dataclass(kw_only=True)
 class SensitiveAttachment(Attachment):
     sensitive: bool
 
 
+# link to the post on the current service
 @dataclass(kw_only=True)
 class RemoteUrlAttachment(Attachment):
     url: str
 
 
+# any media attachment. image, video, audio, flash games, etc.
 @dataclass(kw_only=True)
 class MediaAttachment(Attachment):
     blobs: list[Blob]
 
 
+# quote of some post on the same service
 @dataclass(kw_only=True)
 class QuoteAttachment(Attachment):
     quoted_id: str
     quoted_user: str
 
 
+# embed to an external website
 @dataclass(kw_only=True)
 class ExternalEmbedAttachment(Attachment):
     uri: str
     title: str | None
     desc: str | None
+
+
+# out-of-band tags (the correct kind of tags)
+@dataclass(kw_only=True)
+class TagsAttachment(Attachment):
+    tags: list[str]
diff --git a/mastodon/output.py b/mastodon/output.py
index 15593a3..8f65174 100644
--- a/mastodon/output.py
+++ b/mastodon/output.py
@@ -12,6 +12,7 @@ from cross.attachments import (
     QuoteAttachment,
     RemoteUrlAttachment,
     SensitiveAttachment,
+    TagsAttachment,
 )
 from cross.media import Blob
 from cross.post import Post, PostRef
@@ -299,7 +300,19 @@ class MastodonOutputService(MastodonService, OutputService):
 
             quoted_status_id = quoted_mappings[0]["identifier"]
 
-        post_tokens = post.tokens
+        post_tokens = post.tokens.copy()
+
+        # mastodon doesn't have out-of-band tag posting
+        # so append them at the end of the post
+        oob_tags = post.attachments.get(TagsAttachment)
+        if oob_tags and oob_tags.tags:
+            if post_tokens:
+                post_tokens.append(TextToken(text="\n\n"))
+
+            for tag in oob_tags.tags:
+                post_tokens.append(TagToken(tag=tag))
+                post_tokens.append(TextToken(text=" "))
+
         if (
             post.text_type == "text/x.misskeymarkdown"
             and self.instance_info.text_format != "text/x.misskeymarkdown"