diff --git a/nanobot/agent/tools/shell.py b/nanobot/agent/tools/shell.py
index d1ad36359..3412a11a7 100644
--- a/nanobot/agent/tools/shell.py
+++ b/nanobot/agent/tools/shell.py
@@ -106,7 +106,7 @@ class ExecTool(Tool):
             r"\brm\s+-[rf]{1,2}\b",          # rm -r, rm -rf, rm -fr
             r"\bdel\s+/[fq]\b",              # del /f, del /q
             r"\brmdir\s+/s\b",               # rmdir /s
-            r"(?:^|[;&|]\s*)format\b",       # format (as standalone command only)
+            r"(?:^|[;&|]\s*)format(?!=)\b",   # format (as standalone command only)
             r"\b(mkfs|diskpart)\b",          # disk operations
             r"\bdd\s+if=",                   # dd
             r">\s*/dev/sd",                  # write to disk
diff --git a/tests/tools/test_exec_security.py b/tests/tools/test_exec_security.py
index 844d535c0..fb6731f03 100644
--- a/tests/tools/test_exec_security.py
+++ b/tests/tools/test_exec_security.py
@@ -243,3 +243,44 @@ def test_exec_still_blocks_real_outside_path_via_redirect(tmp_path):
     blocked = tool._guard_command("echo pwn > /etc/issue", str(workspace))
     assert blocked is not None
     assert "path outside working dir" in blocked
+
+
+# --- format command blocking -----------------------------------------------
+
+
+@pytest.mark.parametrize(
+    "command",
+    [
+        "format C: /q",
+        "format D: /fs:ntfs",
+        "&& format",
+        "| format",
+        "&format",
+        ";format",
+        "|format",
+    ],
+)
+def test_exec_blocks_format_command(command):
+    """The Windows ``format`` disk command must be denied."""
+    tool = ExecTool()
+    result = tool._guard_command(command, "/tmp")
+    assert result is not None
+    assert "deny pattern filter" in result.lower()
+
+
+@pytest.mark.parametrize(
+    "command",
+    [
+        # URL parameter &format= must NOT be blocked (regression).
+        'curl -s "wttr.in/xxx?lang=zh&format=%l:+%c+%t+%h+%w&1"',
+        'curl -s "wttr.in/xxx?format=%l:+%c+%t+%h+%w&1"',
+        # format as a non-command word in a normal argument.
+        "echo format",
+        "echo reformat",
+    ],
+)
+def test_exec_allows_format_in_url_and_args(command):
+    """``format`` inside URL parameters or as a non-command arg must be allowed."""
+    tool = ExecTool()
+    result = tool._guard_command(command, "/tmp")
+    assert result is None