diff --git a/nanobot/agent/tools/shell.py b/nanobot/agent/tools/shell.py
index 18eff64..9c6f1f6 100644
--- a/nanobot/agent/tools/shell.py
+++ b/nanobot/agent/tools/shell.py
@@ -26,7 +26,8 @@ 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"\b(format|mkfs|diskpart)\b",   # disk operations
+            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
             r"\b(shutdown|reboot|poweroff)\b",  # system power
diff --git a/tests/test_exec_curl.py b/tests/test_exec_curl.py
new file mode 100644
index 0000000..2f53fcf
--- /dev/null
+++ b/tests/test_exec_curl.py
@@ -0,0 +1,97 @@
+r"""Tests for ExecTool safety guard — format pattern false positive.
+
+The old deny pattern `\b(format|mkfs|diskpart)\b` matched "format" inside
+URLs (e.g. `curl https://wttr.in?format=3`) because `?` is a non-word
+character, so `\b` fires between `?` and `f`.
+
+The fix splits the pattern:
+  - `(?:^|[;&|]\s*)format\b`  — only matches `format` as a standalone command
+  - `\b(mkfs|diskpart)\b`     — kept as-is (unique enough to not false-positive)
+"""
+
+import re
+
+import pytest
+
+from nanobot.agent.tools.shell import ExecTool
+
+
+# --- Guard regression: "format" in URLs must not be blocked ---
+
+
+@pytest.mark.asyncio
+async def test_curl_with_format_in_url_not_blocked():
+    """curl with ?format= in URL should NOT be blocked by the guard."""
+    tool = ExecTool(working_dir="/tmp")
+    result = await tool.execute(
+        command="curl -s 'https://wttr.in/Brooklyn?format=3'"
+    )
+    assert "blocked by safety guard" not in result
+
+
+@pytest.mark.asyncio
+async def test_curl_with_format_in_post_body_not_blocked():
+    """curl with 'format=json' in POST body should NOT be blocked."""
+    tool = ExecTool(working_dir="/tmp")
+    result = await tool.execute(
+        command="curl -s -d 'format=json' https://httpbin.org/post"
+    )
+    assert "blocked by safety guard" not in result
+
+
+@pytest.mark.asyncio
+async def test_curl_without_format_not_blocked():
+    """Plain curl commands should pass the guard."""
+    tool = ExecTool(working_dir="/tmp")
+    result = await tool.execute(command="curl -s https://httpbin.org/get")
+    assert "blocked by safety guard" not in result
+
+
+# --- The guard still blocks actual format commands ---
+
+
+@pytest.mark.asyncio
+async def test_guard_blocks_standalone_format_command():
+    """'format c:' as a standalone command must be blocked."""
+    tool = ExecTool(working_dir="/tmp")
+    result = await tool.execute(command="format c:")
+    assert "blocked by safety guard" in result
+
+
+@pytest.mark.asyncio
+async def test_guard_blocks_format_after_semicolon():
+    """'echo hi; format c:' must be blocked."""
+    tool = ExecTool(working_dir="/tmp")
+    result = await tool.execute(command="echo hi; format c:")
+    assert "blocked by safety guard" in result
+
+
+@pytest.mark.asyncio
+async def test_guard_blocks_format_after_pipe():
+    """'echo hi | format' must be blocked."""
+    tool = ExecTool(working_dir="/tmp")
+    result = await tool.execute(command="echo hi | format")
+    assert "blocked by safety guard" in result
+
+
+# --- Regex unit tests (no I/O) ---
+
+
+def test_format_pattern_blocks_disk_commands():
+    """The tightened pattern still catches actual format commands."""
+    pattern = r"(?:^|[;&|]\s*)format\b"
+
+    assert re.search(pattern, "format c:")
+    assert re.search(pattern, "echo hi; format c:")
+    assert re.search(pattern, "echo hi | format")
+    assert re.search(pattern, "cmd && format d:")
+
+
+def test_format_pattern_allows_urls_and_flags():
+    """The tightened pattern does NOT match format inside URLs or flags."""
+    pattern = r"(?:^|[;&|]\s*)format\b"
+
+    assert not re.search(pattern, "curl https://wttr.in?format=3")
+    assert not re.search(pattern, "echo --output-format=json")
+    assert not re.search(pattern, "curl -d 'format=json' https://api.example.com")
+    assert not re.search(pattern, "python -c 'print(\"{:format}\".format(1))'")