This blog contains some handy var dumping tips. For example, to dump the setup facts:

# Dump facts for domain example.com
ansible -i inventory_file  some_host -m setup

Another one is to dump all the vars for everything for some serious debugging. Save this to it’s own yml file.

---
- name: dump all
  hosts: all
 
  tasks:
    - name: Print some debug information 
      vars: 
        msg: |
          Module Variables ("vars"):
          --------------------------------
          {{ vars | to_nice_json }} 
          
          Environment Variables ("environment"):
          --------------------------------
          {{ environment | to_nice_json }} 
          
          GROUP NAMES Variables ("group_names"):
          --------------------------------
          {{ group_names | to_nice_json }}
          
          GROUPS Variables ("groups"):
          --------------------------------
          {{ groups | to_nice_json }}
          
          HOST Variables ("hostvars"):
          --------------------------------
          {{ hostvars | to_nice_json }} 
    
      debug: 
        msg: "{{ msg.split('\n') }}"       
      tags: debug_info

Beware – you can get a lot of output, but can be useful if you are trying to find out what vars are defined and which are overridden when you’ve got them set in groups, hosts and roles!