diff --git a/ahtcg_bot.py b/ahtcg_bot.py
index a7b2578..8a09755 100755
--- a/ahtcg_bot.py
+++ b/ahtcg_bot.py
@@ -8,6 +8,7 @@ import discord
 from discord.ext import commands, tasks
 
 from arkhamdb import ArkhamDBClient, ArkhamDBDeck
+from validate_decks import Validator
 from secret import TOKEN
 
 
@@ -119,16 +120,30 @@ class ArkhamDBUpdater(commands.Bot):
                 self.status_for_deck(prefix, deck)
                 for prefix, deck in latest_decks.values()
             )
+
             message_embed = discord.Embed(
                 title=f"Updated as of {datetime.now()}", description=message_text
             )
 
+            cards = await self.arkhamdb_client.get_cards()
+            validator = Validator(cards)
+            validation_errors = list(
+                validator.validate([deck for _, deck in latest_decks.values()])
+            )
+            if validation_errors:
+                message_embed.add_field(
+                    name="Card overuse:", value="\n".join(validation_errors)
+                )
+
             if (
                 last_message is not None
                 and last_message.author.id == self.user.id
                 and len(last_message.embeds) == 1
             ):
-                if message_text != last_message.embeds[0].description:
+                if (
+                    message_embed.description != last_message.embeds[0].description
+                    or message_embed.fields != last_message.embeds[0].fields
+                ):
                     await last_message.edit(embed=message_embed)
             else:
                 await channel.send(embed=message_embed)
diff --git a/arkhamdb.py b/arkhamdb.py
index b53b695..1f4ead2 100644
--- a/arkhamdb.py
+++ b/arkhamdb.py
@@ -1,9 +1,12 @@
-from typing import TypedDict, Optional, Union
+from collections.abc import Iterator
+from typing import TypedDict, Optional, Union, Any
 
 import aiohttp
 
 ARKHAMDB_ORIGIN = "https://arkhamdb.adamgoldsmith.name"
 
+ArkhamDBCard = Any
+
 
 class ArkhamDBDeck(TypedDict):
     id: int
@@ -42,6 +45,10 @@ class ArkhamDBClient:
     async def close(self) -> None:
         await self._session.close()
 
+    async def get_cards(self) -> list[ArkhamDBCard]:
+        async with self._session.get(self.origin + "/api/public/cards/") as resp:
+            return await resp.json()
+
     async def get_latest_deck(self, deck_id: int) -> ArkhamDBDeck:
         next_deck_id = deck_id
         deck = None
diff --git a/validate_decks.py b/validate_decks.py
new file mode 100644
index 0000000..f8b3791
--- /dev/null
+++ b/validate_decks.py
@@ -0,0 +1,32 @@
+from collections import defaultdict
+from collections.abc import Iterator
+
+from arkhamdb import ArkhamDBCard, ArkhamDBDeck
+
+
+class Validator:
+    cards_by_code: dict[str, ArkhamDBCard]
+
+    def __init__(self, cards: list[ArkhamDBCard]) -> None:
+        cards: list[ArkhamDBCard]
+        self.cards_by_code = {card["code"]: card for card in cards}
+
+    def validate(self, decks: list[ArkhamDBDeck]) -> Iterator[str]:
+        card_total_counts = defaultdict(lambda: 0)
+        for deck in decks:
+            for code, count in deck["slots"].items():
+                card_total_counts[code] += count
+
+        for code, count in card_total_counts.items():
+            try:
+                card = self.cards_by_code[code]
+                quantity = card["quantity"]
+                # assume two copies of the core set
+                if card["pack_code"] == "core":
+                    quantity = quantity * 2
+
+                if count > quantity:
+                    in_decks = [deck["id"] for deck in decks if code in deck["slots"]]
+                    yield f"Too many copies of {card['name']}! ({count} > {quantity}), in decks {in_decks}"
+            except KeyError:
+                yield f'Did not find card with code "{code}"'