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+# no-changed-when
+
+This rule checks that tasks return changes to results or conditions. Unless
+tasks only read information, you should ensure that they return changes in the
+following ways:
+
+- Register results or conditions and use the `changed_when` clause.
+- Use the `creates` or `removes` argument.
+
+You should always use the `changed_when` clause on tasks that do not naturally
+detect if a change has occurred or not. Some of the most common examples are
+[shell] and [command] modules, which run arbitrary commands.
+
+One very common workaround is to use a boolean value like `changed_when: false`
+if the task never changes anything or `changed_when: true` if it always changes
+something, but you can also use any expressions, including ones that use the
+registered result of a task, like in our example below.
+
+This rule also applies to handlers, not only to tasks because they are also
+tasks.
+
+## Problematic Code
+
+```yaml
+---
+- name: Example playbook
+  hosts: localhost
+  tasks:
+    - name: Does not handle any output or return codes
+      ansible.builtin.command: cat {{ my_file | quote }} # <- Does not handle the command output.
+```
+
+## Correct Code
+
+```yaml
+---
+- name: Example playbook
+  hosts: localhost
+  tasks:
+    - name: Handle shell output with return code
+      ansible.builtin.command: cat {{ my_file | quote }}
+      register: my_output # <- Registers the command output.
+      changed_when: my_output.rc != 0 # <- Uses the return code to define when the task has changed.
+```
+
+[shell]:
+  https://docs.ansible.com/ansible/latest/collections/ansible/builtin/shell_module.html
+[command]:
+  https://docs.ansible.com/ansible/latest/collections/ansible/builtin/command_module.html