diff --git a/data/settings.json b/data/settings.json
index bcbd20a..9ee2d23 100644
--- a/data/settings.json
+++ b/data/settings.json
@@ -13,7 +13,8 @@
     "admin_command_list": [
         "shrug",
         "emoji_size",
-        "emoji_list"
+        "emoji_list",
+        "mutual_rooms"
     ],
     "command_list": [
         "ping",
@@ -32,7 +33,8 @@
         "shrug": "{prefix}shrug {text}: Append ¯\\_(ツ)_/¯ to the text",
         "emoji_size": "{prefix}emoji_size {size}: Set the default emoji size",
         "emoji_list": "{prefix}emoji_list: Get a list of usable custom emojis",
-        "aw": "{prefix}aw (Search term): Search the Arch Wiki"
+        "aw": "{prefix}aw (Search term): Search the Arch Wiki",
+        "mutual_rooms": "{prefix}mutual_rooms {user}: Get list of rooms shared with user"
     },
     "source_url": "https://g.deadca.de/deadcade/Matrix-Selfbot"
 }
diff --git a/main.py b/main.py
index 406a465..2549a07 100644
--- a/main.py
+++ b/main.py
@@ -12,7 +12,7 @@ import requests # XKCD command
 import difflib # XKCD Title lookup
 import subprocess # GIF Emojis, ping command (admin)
 import random # roll command, http cat without args
-import datetime # Ratelimiting
+import datetime # Ratelimiting, room member cache invalidation
 
 # External dependencies
 import nio # Matrix library, matirx-nio[e2e]
@@ -59,6 +59,7 @@ credentials = load_data(settings["credentials_path"])
 # Set up global variables
 client = None
 ratelimits = {}
+room_member_cache = {}
 
 # Common function definitions
 # Filter a title for local lookup with XKCD
@@ -128,7 +129,7 @@ def resize_image(filename, size):
 
 # Mentions a user
 def mention(user):
-    return f"[{user.split(':')[0][1:]}](https://matrix.to/#/{user})"
+    return f"<a href=\"https://matrix.to/#/{user}\">{user.split(':')[0][1:]}</a>"
 
 # Send file to homeserver
 async def send_file(filename):
@@ -324,6 +325,55 @@ async def aw(args, room, event):
     else:
         return await send_text(room.room_id, "Please provide a search term.")
 
+async def mutual_rooms(args, room, event):
+    global client, room_member_cache
+    # Custom arg parser, because we need to use formatted_body for mentions from modern clients
+    if len(args) > 0:
+        args = event.formatted_body.split(" ")[1:] if event.formatted_body else event.body.split(" ")[1:]
+    user = ""
+    for arg in args:
+        if arg.startswith("href"):
+            # Parse user from a matrix.to link
+            try:
+                user = "@" + arg.replace("%40", "@").replace("%3A", ":").split("@")[1].split('"')[0]
+            except Exception:
+                pass
+            break
+        elif arg.startswith("@"):
+            # User is direct text
+            user = arg
+            break
+    if not user:
+        return await send_text(room.room_id, "Error parsing user MXID")
+
+    # Create a list of mutual rooms
+    # Determine if the cache is usable
+    usecache = "date" in room_member_cache and room_member_cache["date"] > int(datetime.datetime.utcnow().timestamp())
+    mutual = []
+    # Get list of rooms the bot user is in
+    joined_rooms = await client.joined_rooms()
+    # If cache is invalid
+    if not usecache:
+        # Reset the cache timestamp
+        room_member_cache["date"] = int(datetime.datetime.utcnow().timestamp()) + 1800
+    # Check every room
+    for lroom in joined_rooms.rooms:
+        members = []
+        # If there's a valid cache entry
+        if usecache and lroom in room_member_cache:
+            # Use cache
+            members = room_member_cache[lroom]
+        else:
+            # Grab room member list from HS and store it in cache
+            members = await client.joined_members(lroom)
+            members = members.members
+            room_member_cache[lroom] = members
+        # Check if user is in room
+        if user in [x.user_id for x in members]:
+            mutual.append(lroom)
+    # Send room list
+    return await send_text(room.room_id, "List of mutual rooms with " + mention(user) + ":\n" + "\n".join([f"<a href=\"https://matrix.to/#/{x.replace(':', '%3A')}\">{x}</a>" for x in mutual]) + "\n")
+
 async def unknown_callback(room: nio.MatrixRoom, event: nio.UnknownEvent) -> None:
     if event.type == "m.reaction":
         # Get the ID of the event this was a reaction to