Ansible YAML Indentation Error: How to Fix It (Examples)

Today we’re going to talk about Ansible troubleshooting and specifically about indentation errors. I’m Luca Berton and welcome to today’s episode of Ansible Pilot

Demo

The best way of talking about Ansible troubleshooting is to jump in a live Playbook to show you practically the error and how to solve it!

Error

---
- name: blockinfile module demo
  hosts: all
  become: true
  tasks:
- name: Generate /etc/hosts file
  ansible.builtin.blockinfile:
    state: present
    dest: /etc/hosts
    content: |
      192.168.0.200 Playbook demo.example.com

Fix

---
- name: blockinfile module demo
  hosts: all
  become: true
  tasks:
  - name: Generate /etc/hosts file
      ansible.builtin.blockinfile:
        state: present
        dest: /etc/hosts
        content: |
          192.168.0.200 Playbook demo.example.com

code with ❤️ in GitHub

See also: Ansible troubleshooting - Error parser-error

Conclusion

Now you know better how to troubleshoot the most common Ansible error about indentation.

Understanding YAML Indentation in Ansible

YAML (YAML Ain't Markup Language) is whitespace-sensitive. Ansible playbooks are written in YAML, which means indentation determines the structure of your configuration. Unlike Python (which uses 4 spaces by default), YAML is flexible about the number of spaces, but you must be consistent.

The Golden Rules

Never use tabs — YAML only accepts spaces Be consistent — pick 2 spaces (Ansible standard) and stick with it List items (-) must be at the same indentation level as their siblings Key-value pairs under a mapping must be indented deeper than the parent

See also: Ansible troubleshooting - AWS Failed to import the required Python library (botocore or boto3)

Common Indentation Errors

Error 1: Tasks not indented under tasks:

# ❌ WRONG — task is at same level as tasks key
- name: my playbook
  hosts: all
  tasks:
  - name: install package
    ansible.builtin.apt:
      name: curl

# ✅ CORRECT — task is indented under tasks
- name: my playbook
  hosts: all
  tasks:
    - name: install package
      ansible.builtin.apt:
        name: curl

Error 2: Module parameters not indented under module name

# ❌ WRONG — path is at same level as file module
    - name: create file
      ansible.builtin.file:
      path: /tmp/test
      state: touch

# ✅ CORRECT — path is indented under file module
    - name: create file
      ansible.builtin.file:
        path: /tmp/test
        state: touch

Error 3: Mixing tabs and spaces

This is invisible but devastating. Your editor might insert tabs that look like spaces. Use cat -A playbook.yml to reveal tabs (shown as ^I).

# Check for hidden tabs
$ cat -A playbook.yml | grep "\^I"

Error 4: Inconsistent indentation depth

# ❌ WRONG — mixed 2-space and 4-space indentation
- name: my playbook
  hosts: all
  tasks:
    - name: first task
      ansible.builtin.debug:
        msg: "hello"
    - name: second task
      ansible.builtin.debug:
          msg: "world"  # 4 extra spaces instead of 2!

How to Prevent Indentation Errors

1. Use ansible-lint

pip install ansible-lint
ansible-lint playbook.yml

2. Use yamllint

pip install yamllint
yamllint playbook.yml

3. Configure your editor

VS Code — Install the "YAML" extension by Red Hat and add to settings.json:

{
  "[yaml]": {
    "editor.tabSize": 2,
    "editor.insertSpaces": true,
    "editor.detectIndentation": false
  }
}

vim — Add to .vimrc:

autocmd FileType yaml setlocal ts=2 sts=2 sw=2 expandtab

4. Use --syntax-check before running

ansible-playbook playbook.yml --syntax-check

See also: Ansible Vault Error: Fix 'Attempting to Decrypt but No Vault Secrets Found'

FAQ

Why does Ansible use YAML?

YAML is human-readable, widely supported, and doesn't require closing tags or brackets. However, its whitespace sensitivity means indentation errors are the #1 most common Ansible problem.

Can I use 4 spaces instead of 2?

Yes, but the Ansible community standard is 2 spaces. The important thing is consistency within a file.

How do I fix "mapping values are not allowed here"?

This almost always means a colon (:) in a value that YAML is interpreting as a key-value separator. Either quote the value or fix the indentation:

# ❌ Triggers error
msg: Error: something broke
# ✅ Fix with quotes
msg: "Error: something broke"

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