diff --git a/tools/terminal_tool.py b/tools/terminal_tool.py
index 6572174819af7..1768f80aed3c7 100644
--- a/tools/terminal_tool.py
+++ b/tools/terminal_tool.py
@@ -189,8 +189,24 @@ def _check_vercel_sandbox_requirements(config: dict[str, Any]) -> bool:
     return False
 
 
+# Cache for disk usage warning to avoid full rglob scan on every call.
+# The check is advisory-only — staleness for up to 5 minutes is acceptable.
+_disk_usage_cache: dict = {"timestamp": 0.0, "result": False}
+_DISK_USAGE_CACHE_TTL = 300.0  # seconds
+
+
 def _check_disk_usage_warning():
-    """Check if total disk usage exceeds warning threshold."""
+    """Check if total disk usage exceeds warning threshold.
+
+    Result is cached for :data:`_DISK_USAGE_CACHE_TTL` seconds (default:
+    5 minutes) to avoid an expensive recursive filesystem scan on every
+    terminal command.  The check is advisory-only so a stale result is
+    harmless.
+    """
+    import time as _time_mod
+    now = _time_mod.monotonic()
+    if now - _disk_usage_cache["timestamp"] < _DISK_USAGE_CACHE_TTL:
+        return _disk_usage_cache["result"]
     try:
         scratch_dir = _get_scratch_dir()
 
@@ -207,14 +223,16 @@ def _check_disk_usage_warning():
         
         total_gb = total_bytes / (1024 ** 3)
         
-        if total_gb > DISK_USAGE_WARNING_THRESHOLD_GB:
+        exceeded = total_gb > DISK_USAGE_WARNING_THRESHOLD_GB
+        if exceeded:
             logger.warning("Disk usage (%.1fGB) exceeds threshold (%.0fGB). Consider running cleanup_all_environments().",
                            total_gb, DISK_USAGE_WARNING_THRESHOLD_GB)
-            return True
-        
-        return False
+        _disk_usage_cache["timestamp"] = _time_mod.monotonic()
+        _disk_usage_cache["result"] = exceeded
+        return exceeded
     except Exception as e:
         logger.debug("Disk usage warning check failed: %s", e, exc_info=True)
+        # Don't update cache on error so the next call retries.
         return False