diff --git a/pycodeloop/tools/env.py b/pycodeloop/tools/env.py
index 0a34de3..ee29a86 100644
--- a/pycodeloop/tools/env.py
+++ b/pycodeloop/tools/env.py
@@ -55,6 +55,14 @@ class EnvTool(Tool):
             "name": {"type": "string"},
         },
     }
+    dangerous = True
+
+    def preview(self, name: str = "", **_) -> str:
+        return (
+            f"$ env {name}"
+            if name
+            else "$ env (list all variable names and masked values)"
+        )
 
     def run(self, name: str = "") -> ToolResult:
         if name:
diff --git a/tests/tools/test_env.py b/tests/tools/test_env.py
index 947a6ca..78f4068 100644
--- a/tests/tools/test_env.py
+++ b/tests/tools/test_env.py
@@ -61,6 +61,19 @@ def test_masks_pass_variants_and_auth(self):
         self.assertIn("SESSION_ID=***", result.output)
         self.assertIn("HOME=/tmp", result.output)
 
+    def test_is_dangerous_and_requires_confirmation(self):
+        self.assertTrue(EnvTool().dangerous)
+
+    def test_preview_names_the_single_variable_being_read(self):
+        self.assertEqual(
+            EnvTool().preview(name="MY_API_KEY"), "$ env MY_API_KEY"
+        )
+
+    def test_preview_warns_about_listing_every_variable(self):
+        preview = EnvTool().preview()
+
+        self.assertIn("all variable names and masked values", preview)
+
 
 if __name__ == "__main__":
     unittest.main()