Filters highlighted by Ansible : 

https://docs.ansible.com/ansible/latest/user_guide/playbooks_filters.html

List of Jinja2 Filters :

https://jinja.palletsprojects.com/en/2.11.x/templates/#builtin-filters

Common used Filters : 

- {‌{ my_var | default("myval") }} : assign default value "myval" to the variable "my_var" if it not defined.

- {‌{ user_password | password_hash('sha512') }} : transform the variable value to a sha512 password hash . Useful when using "user" module to create/update users with their passwords.

- The following filters change the format of the variable data structure to json or yaml or even to a pretty json or yaml :

{‌{ some_variable | to_json }}
{‌{ some_variable | to_yaml }}
{‌{ some_variable | to_nice_json }}
{‌{ some_variable | to_nice_yaml }}