diff --git a/tests/test_permissions.py b/tests/test_permissions.py
new file mode 100644
index 0000000..bc3023e
--- /dev/null
+++ b/tests/test_permissions.py
@@ -0,0 +1,87 @@
+from __future__ import annotations
+
+import unittest
+
+from src.permissions import ToolPermissionContext
+
+
+class TestToolPermissionContext(unittest.TestCase):
+    # 1. Empty context blocks nothing
+    def test_empty_context_blocks_nothing(self) -> None:
+        ctx = ToolPermissionContext()
+        self.assertFalse(ctx.blocks("anything"))
+        self.assertFalse(ctx.blocks(""))
+
+    # 2. Exact name blocking (case insensitive)
+    def test_exact_name_blocking(self) -> None:
+        ctx = ToolPermissionContext.from_iterables(deny_names=["dangerous_tool"])
+        self.assertTrue(ctx.blocks("dangerous_tool"))
+        self.assertTrue(ctx.blocks("Dangerous_Tool"))
+        self.assertTrue(ctx.blocks("DANGEROUS_TOOL"))
+        self.assertFalse(ctx.blocks("safe_tool"))
+
+    # 3. Prefix blocking (case insensitive)
+    def test_prefix_blocking(self) -> None:
+        ctx = ToolPermissionContext.from_iterables(deny_prefixes=["admin_"])
+        self.assertTrue(ctx.blocks("admin_delete"))
+        self.assertTrue(ctx.blocks("Admin_Delete"))
+        self.assertTrue(ctx.blocks("ADMIN_CREATE"))
+        self.assertFalse(ctx.blocks("user_admin"))
+
+    # 4. Combined name + prefix blocking
+    def test_combined_name_and_prefix_blocking(self) -> None:
+        ctx = ToolPermissionContext.from_iterables(
+            deny_names=["rm"],
+            deny_prefixes=["sudo_"],
+        )
+        self.assertTrue(ctx.blocks("rm"))
+        self.assertTrue(ctx.blocks("sudo_restart"))
+        self.assertFalse(ctx.blocks("ls"))
+
+    # 5. Non-matching names are allowed
+    def test_non_matching_names_allowed(self) -> None:
+        ctx = ToolPermissionContext.from_iterables(
+            deny_names=["blocked"],
+            deny_prefixes=["bad_"],
+        )
+        self.assertFalse(ctx.blocks("allowed"))
+        self.assertFalse(ctx.blocks("good_tool"))
+        self.assertFalse(ctx.blocks("not_bad"))
+
+    # 6. from_iterables with None args
+    def test_from_iterables_none_args(self) -> None:
+        ctx = ToolPermissionContext.from_iterables(deny_names=None, deny_prefixes=None)
+        self.assertEqual(ctx.deny_names, frozenset())
+        self.assertEqual(ctx.deny_prefixes, ())
+        self.assertFalse(ctx.blocks("anything"))
+
+    def test_from_iterables_default_args(self) -> None:
+        ctx = ToolPermissionContext.from_iterables()
+        self.assertEqual(ctx.deny_names, frozenset())
+        self.assertEqual(ctx.deny_prefixes, ())
+
+    # 7. from_iterables normalizes to lowercase
+    def test_from_iterables_normalizes_to_lowercase(self) -> None:
+        ctx = ToolPermissionContext.from_iterables(
+            deny_names=["FooBar"],
+            deny_prefixes=["PFX_"],
+        )
+        self.assertIn("foobar", ctx.deny_names)
+        self.assertNotIn("FooBar", ctx.deny_names)
+        self.assertEqual(ctx.deny_prefixes, ("pfx_",))
+        self.assertTrue(ctx.blocks("FOOBAR"))
+        self.assertTrue(ctx.blocks("pfx_something"))
+
+    # 8. Multiple deny_names
+    def test_multiple_deny_names(self) -> None:
+        ctx = ToolPermissionContext.from_iterables(
+            deny_names=["tool_a", "tool_b", "tool_c"],
+        )
+        self.assertTrue(ctx.blocks("tool_a"))
+        self.assertTrue(ctx.blocks("tool_b"))
+        self.assertTrue(ctx.blocks("tool_c"))
+        self.assertFalse(ctx.blocks("tool_d"))
+
+
+if __name__ == "__main__":
+    unittest.main()