This is likely hair splitting, but you are far more likely getting bitten by the monster amount of variance in jinja2 versions/behaviors than by anything "yaml-y"

For example, yaml does not care about this whatsoever

  - name: skip on Tuesdays
    when: ansible_date_time.weekday != "Tuesday"

but different ansible versions are pretty yolo about whether one needs to additionally wrap those fields in jinja2 mustaches

  - name: skip on Tuesdays
    when: '{{ ansible_date_time.weekday != "Tuesday" }}'

and another common bug is when the user tries to pass in a boolean via "-e" because those are coerced into string key-value pairs as in

  $ ansible -e not_today=true -m debug -a var=not_today all
  localhost | SUCCESS => {
    "not_today": "true"
  }

but if one uses the jinja/python compatible flavor, it does the thing

  $ ansible -e not_today=True -m debug -a var=not_today all
  localhost | SUCCESS => {
    "not_today": true
  }

It may be more work than you care for, since sprinkling rampant |bool likely doesn't actively hurt anything, but the |type_debug filter[1] can help if it's behaving mysteriously

1: https://docs.ansible.com/ansible/11/collections/ansible/buil...

Yep. I just want strict yaml:

anything encased in quotes is a string, anything not is not a string (bool, int or float)

There have been several write-ups about it: https://news.ycombinator.com/item?id=43113997 https://news.ycombinator.com/item?id=15046223

Empty the footgun before firing.

This effectively means that a new version of specification didn't solve the problem at all.