diff --git a/app.py b/app.py
index 72d0711..140c18c 100644
--- a/app.py
+++ b/app.py
@@ -2,6 +2,7 @@ import os
 import select
 import sys
 import time
+import unicodedata
 from collections import deque
 from importlib import import_module
 from pathlib import Path
@@ -53,7 +54,9 @@ TOOL_REGISTRY = {
         "module": "intelligent_tool",
         "class": "IntelligentCommunicationTool",
         "kwargs": {
-            "model": os.environ.get("MISTLE_LLM_MODEL", "mistral/mistral-small")
+            "model": os.environ.get(
+                "MISTLE_LLM_MODEL", "mistral/mistral-small"
+            )
         },
         "description": "Uses an LLM to craft a polite reply to private tells.",
     },
@@ -61,7 +64,9 @@ TOOL_REGISTRY = {
         "module": "intelligent_tool",
         "class": "IntelligentCommunicationTool",
         "kwargs": {
-            "model": os.environ.get("MISTLE_LLM_MODEL", "mistral/mistral-small")
+            "model": os.environ.get(
+                "MISTLE_LLM_MODEL", "mistral/mistral-small"
+            )
         },
         "description": "Alias of 'intelligent'. Uses an LLM to craft a polite reply to private tells.",
     },
@@ -74,6 +79,38 @@ TOOL_DESCRIPTIONS = {
 from telnetclient import TelnetClient
 
 
+_UMLAUT_TRANSLATION = str.maketrans(
+    {
+        "ä": "ae",
+        "ö": "oe",
+        "ü": "ue",
+        "Ä": "Ae",
+        "Ö": "Oe",
+        "Ü": "Ue",
+        "ß": "ss",
+    }
+)
+
+
+def sanitize_for_mud(text: str) -> str:
+    """Return ASCII-only text suitable for Silberland's input parser."""
+    if not text:
+        return ""
+
+    replaced = text.translate(_UMLAUT_TRANSLATION)
+    normalized = unicodedata.normalize("NFKD", replaced)
+    cleaned: list[str] = []
+    for ch in normalized:
+        if unicodedata.combining(ch):
+            continue
+        code = ord(ch)
+        if 32 <= code <= 126:
+            cleaned.append(ch)
+        else:
+            cleaned.append("?")
+    return "".join(cleaned)
+
+
 class SessionState:
     """Share Telnet session state safely across threads."""
 
@@ -113,8 +150,9 @@ class SessionState:
         self._listeners_lock = Lock()
 
     def send(self, client: TelnetClient, message: str) -> None:
+        sanitized = sanitize_for_mud(message)
         with self._send_lock:
-            client.send(message)
+            client.send(sanitized)
 
     def tool_send(
         self,
@@ -125,12 +163,14 @@ class SessionState:
         stop_event: Event,
     ) -> bool:
         """Send on behalf of the tool while respecting a minimum cadence."""
+        sanitized = sanitize_for_mud(message)
+
         while not stop_event.is_set():
             with self._send_lock:
                 now = time.time()
                 elapsed = now - self._last_tool_send
                 if elapsed >= min_interval:
-                    client.send(message)
+                    client.send(sanitized)
                     self._last_tool_send = now
                     return True
                 wait_time = min_interval - elapsed
@@ -340,10 +380,10 @@ def login(
             state.update_output(banner)
 
     if user:
-        client.send(user)
+        client.send(sanitize_for_mud(user))
         time.sleep(0.2)
     if password:
-        client.send(password)
+        client.send(sanitize_for_mud(password))
 
     response = client.receive(timeout=response_timeout)
     if response:
@@ -414,7 +454,7 @@ def graceful_shutdown(
         if state:
             state.send(client, exit_command)
         else:
-            client.send(exit_command)
+            client.send(sanitize_for_mud(exit_command))
         farewell = client.receive(timeout=2.0)
         if farewell:
             print(farewell, end="" if farewell.endswith("\n") else "\n")