diff --git a/src/specify_cli/extensions/__init__.py b/src/specify_cli/extensions/__init__.py
index c22445ebe0..dabde70bbc 100644
--- a/src/specify_cli/extensions/__init__.py
+++ b/src/specify_cli/extensions/__init__.py
@@ -432,9 +432,13 @@ def _validate(self):
                             f"Invalid hook '{hook_name}': "
                             "expected a mapping or list of mappings"
                         )
-                    if not entry.get("command"):
+                    command = entry.get("command")
+                    # #5080: same rule as validate_events() in events/__init__.py.
+                    # A truthy non-string (e.g. command: [foo]) passed a bare
+                    # truthiness check and crashed hook registration mid-install.
+                    if not isinstance(command, str) or not command.strip():
                         raise ValidationError(
-                            f"Hook '{hook_name}' missing required 'command' field"
+                            f"Hook '{hook_name}' missing required 'command' string"
                         )
                     if "priority" in entry:
                         priority = entry["priority"]
diff --git a/tests/specify_cli/extensions/test_command_add.py b/tests/specify_cli/extensions/test_command_add.py
index 44423b5fdc..f898fa052f 100644
--- a/tests/specify_cli/extensions/test_command_add.py
+++ b/tests/specify_cli/extensions/test_command_add.py
@@ -40,6 +40,34 @@
 class TestExtensionAddCLI:
     """CLI tests for ``specify extension add``."""
 
+    @pytest.mark.parametrize("command", [
+        pytest.param(["speckit.test-ext.hello"], id="list"),
+        pytest.param({"name": "speckit.test-ext.hello"}, id="mapping"),
+    ])
+    def test_add_dev_rejects_invalid_hook_command_before_writing_files(
+        self, extension_dir, project_dir, command
+    ):
+        """Malformed hook commands must leave no installed artifacts (#5080)."""
+        manifest_path = extension_dir / "extension.yml"
+        data = yaml.safe_load(manifest_path.read_text(encoding="utf-8"))
+        data["hooks"]["after_tasks"]["command"] = command
+        manifest_path.write_text(yaml.safe_dump(data), encoding="utf-8")
+        agent_dir = project_dir / ".claude"
+        (agent_dir / "skills").mkdir(parents=True)
+        before = set(agent_dir.rglob("*"))
+
+        with patch.object(Path, "cwd", return_value=project_dir):
+            result = CliRunner().invoke(app, ["extension", "add", "--dev", str(extension_dir)])
+
+        assert result.exit_code == 1, result.output
+        assert isinstance(result.exception, SystemExit), repr(result.exception)
+        output = strip_ansi(result.output)
+        assert "after_tasks" in output and "'command'" in output, output
+        assert "Traceback" not in output
+        assert not (project_dir / ".specify/extensions/test-ext").exists()
+        assert set(agent_dir.rglob("*")) == before
+        assert ExtensionRegistry(project_dir / ".specify/extensions").get("test-ext") is None
+
     def test_add_dev_links_copilot_agent_when_supported(
         self, extension_dir, project_dir, temp_dir
     ):
diff --git a/tests/test_extensions.py b/tests/test_extensions.py
index f2a75d08a4..07142e9c24 100644
--- a/tests/test_extensions.py
+++ b/tests/test_extensions.py
@@ -878,6 +878,26 @@ def test_non_dict_hook_entry_raises_validation_error(self, temp_dir, valid_manif
         with pytest.raises(ValidationError, match="Invalid hook 'after_tasks'"):
             ExtensionManifest(manifest_path)
 
+    @pytest.mark.parametrize("as_list", [False, True])
+    @pytest.mark.parametrize("command", [
+        pytest.param(["speckit.test-ext.hello"], id="list"),
+        pytest.param({"name": "speckit.test-ext.hello"}, id="mapping"),
+        pytest.param(123, id="integer"),
+        pytest.param(True, id="boolean"),
+        pytest.param("  ", id="blank"),
+    ])
+    def test_hook_command_must_be_a_string(
+        self, temp_dir, valid_manifest_data, command, as_list
+    ):
+        """Reject non-string commands before hook registration can fail (#5080)."""
+        entry = {"command": command}
+        valid_manifest_data["hooks"]["after_tasks"] = [entry] if as_list else entry
+        manifest_path = temp_dir / "extension.yml"
+        manifest_path.write_text(yaml.safe_dump(valid_manifest_data), encoding="utf-8")
+
+        with pytest.raises(ValidationError, match="Hook 'after_tasks' missing required 'command' string"):
+            ExtensionManifest(manifest_path)
+
     def test_hook_single_mapping_still_accepted(self, extension_dir):
         """Existing single-mapping hook manifests parse unchanged (regression)."""
         manifest_path = extension_dir / "extension.yml"