YAML Formatter Online

Rule 1: Indentation with Spaces

YAML uses indentation to show structure. Use spaces, not tabs. Each level is typically 2 spaces.

name: MyApp
version: 1.0
server:
  host: localhost
  port: 8080

Rule 2: Key-Value with Colon

Every mapping key must end with a colon : followed by a space. The value comes after the space.

name: "MyApp"      # correct
host: localhost   # correct
# host localhost  # wrong - missing colon

Rule 3: No Duplicate Keys

Keys at the same level must be unique. Duplicate keys will cause a validation error.

# Wrong - duplicate "app":
app:
  name: App1
app:
  name: App2

# Correct - different parent keys:
server1:
  host: localhost
server2:
  host: example.com

Rule 4: Lists with Hyphen

List items start with - (hyphen + space). Nested properties are indented under each item.

fruits:
  - name: Apple
    color: red
  - name: Banana
    color: yellow
  - "Orange"

Rule 5: Quoting Strings

Use quotes for strings with special characters like {}, [], :#, or reserved chars like @ and `.

email: "user@example.com"
path: "/etc/nginx"
message: "key: value pair"
tag: "@mention"  # must be quoted

Rule 6: Comments with Hash

Comments start with # preceded by a space. They can appear on their own line or after a value.

# This is a comment
name: MyApp   # inline comment
version: 2.0

Flow Collections (Inline)

Use {} for mappings and [] for sequences. Brackets must be balanced.

user: {name: John, age: 30}
colors: [red, green, blue]
matrix: [[1, 2], [3, 4]]

Block Scalars

Use | to preserve newlines or > to fold them into one line.

description: |
  This preserves
  line breaks
message: >
  This folds into
  one line

Data Types

YAML supports strings, numbers, booleans, and null without explicit type declarations.

count: 42              # integer
price: 9.99            # float
enabled: true          # boolean
active: yes            # also true
empty: ~               # null
missing: null          # also null

Document Markers

Use --- to start a document and ... to end one. Multiple documents can exist in one file.

---
name: Document1
---
name: Document2
...

Mixed Tabs and Spaces

YAML does not allow mixing tabs and spaces. Use the validator to find and fix these issues. The beautifier converts tabs to spaces automatically.

Missing Colon After Key

Forgetting the : after a key name is one of the most common mistakes. Every key-value pair requires the colon separator.

Orphaned Indentation

Indented content must have a parent key above it. A line indented under a key with a simple value (not a block) will fail validation.

Unclosed Brackets

Every { needs a matching }, and every [ needs a ]. The validator checks for balanced flow collections.

What is a YAML formatter?

A YAML formatter normalizes indentation, spacing, and structure in YAML documents so they are consistent and easy to read. It helps prevent parsing errors caused by inconsistent whitespace.

Is this YAML formatter free?

Yes. All tools are completely free and run locally in your browser. No signup, no limits, no hidden costs.

Does the tool store my data?

No. Your YAML data never leaves your browser. All processing happens locally on your device, ensuring complete privacy and security.

How do I format YAML?

Paste your YAML into the input area and click the "Beautify" button. The tool will normalize all indentation to consistent 2-space levels and format the structure for readability.

What is YAML minification?

Minification removes empty lines, trailing whitespace, and unnecessary blank space to produce a more compact document. Click "Minify" to compress your YAML.

Can I validate my YAML?

Yes! Click the "Validate" button to check your YAML for syntax errors including: mixed tabs/spaces, missing colons, duplicate keys, orphaned indentation, unclosed brackets, reserved characters, and invalid indentation jumps.

Can I use this for Docker Compose or Kubernetes configs?

Yes. Any valid YAML document works — including docker-compose.yml, Kubernetes manifests, Ansible playbooks, GitHub Actions workflows, and more.

My YAML still looks wrong after beautifying.

Make sure your input is valid YAML first. Run the validator to catch issues, fix them, and then re-run the beautifier. Common issues include unquoted special characters and incorrect list formatting.

Can I use this tool offline?

Yes! Once you've visited the page, all functionality works offline thanks to service workers and local processing.