YAML Syntax Check and Validator for YAML & Ansible

Validate YAML online, detect syntax errors, check indentation, review warnings, and fix common YAML and Ansible issues faster.

Language

Live validation Show formatted result Resolve aliases during formatting Support merge key <<

Input YAML

Formatted result

Note: a regular textarea cannot highlight parts of text inside the field. That is why this editor marks line numbers and jumps to the error location.

What this YAML validator checks

This online YAML validator is designed for plain YAML files and Ansible playbooks. It helps identify the kinds of problems that commonly break parsing, deployment, and automation workflows.

YAML syntax errors and parser failures
Indentation problems caused by spaces or tabs
Duplicate keys in the same YAML mapping
Alias, anchor, and merge key issues
Formatting output for easier debugging
Common Ansible playbook quality warnings

Common YAML errors with examples

Bad indentation

YAML is indentation-sensitive. Even one misplaced space can break the whole document.

Bad

items:
 - apple
  - banana

Good

items:
  - apple
  - banana

Missing colon after a key

A mapping key usually needs a colon before the value.

Bad

name John
age: 30

Good

name: John
age: 30

Tabs used for indentation

YAML should use spaces for indentation. Tabs often cause parser errors.

Bad

tasks:
	- debug:
	    msg: hello

Good

tasks:
  - debug:
      msg: hello

Duplicate keys

Using the same key twice in one mapping can hide values and break automation.

Bad

service:
  enabled: true
  enabled: false

Good

service:
  enabled: false

Broken anchors or aliases

An alias must reference an anchor that already exists.

Bad

defaults: *base

Good

defaults: &base
  retries: 3
copy: *base

Quoted values changing data types

Quoted booleans, nulls, or numbers become strings instead of native YAML values.

Bad

enabled: "true"
port: "8080"

Good

enabled: true
port: 8080

Common Ansible YAML issues

Ansible playbooks often fail because YAML structure looks valid at first glance but does not match what the tool expects. This validator helps catch both syntax errors and common playbook mistakes earlier.

Tasks without a clear name
Missing hosts in a play definition
Handlers or vars using the wrong YAML structure
Commands lists indented at the wrong level
Quoted booleans, nulls, and numbers that change data types

YAML validation FAQ

What are the most common YAML syntax errors?

The most common YAML errors are bad indentation, missing colons, duplicate keys, broken lists, and anchors or aliases used incorrectly.

How do I fix YAML indentation errors?

Use spaces consistently, keep items on the same level aligned, and avoid tabs in indentation.

Does this validator support Ansible files?

Yes. The validator can check standard YAML syntax and many common problems seen in Ansible playbooks.

Why is my YAML valid in one tool but invalid in another?

Different tools may apply different YAML versions or extra rules. Duplicate keys, merge keys, and implicit types are common sources of differences.

Can I automatically fix YAML issues?

This tool can automatically fix some simple issues, but structural problems may still need manual review.

Do quoted true or false values stay booleans?

No. In most cases quoted values such as "true" or "false" become strings, not booleans.