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YAML Formatter & Validator — Beautify, Lint, and Convert YAML Online

Free online YAML formatter and validator. Beautify messy YAML, detect errors with line numbers, convert YAML to JSON, view tree structure, and copy results instantly. No upload needed.

Updated

What is the YAML Formatter & Validator — Beautify, Lint, and Convert YAML Online?

Struggling with messy YAML files? Our YAML Formatter and Validator is a free, browser-based tool that instantly beautifies, validates, and converts your YAML — no uploads, no installations, no server round-trips.

Whether you're cleaning up a Kubernetes manifest, debugging a CI config, or converting YAML to JSON, this tool does it all in real time.

What Makes This Tool Different

Feature Most Online Tools Our Tool
Line-numbered error messages ❌ ✅
Tree structure view ❌ ✅
YAML → JSON conversion ⚠️ Basic ✅ Full
Multi-document (---) support ⚠️ Rare ✅
Statistics (keys, arrays, scalars) ❌ ✅
One-click copy ✅ ✅
100% client-side (zero uploads) ❌ ✅

Supported Formats

  • Format / Beautify — Clean up minified or inconsistent YAML with configurable indent (2 or 4 spaces)
  • Validate / Lint — Catch indentation errors, unclosed quotes, duplicate keys, and structural issues with exact line numbers
  • Convert to JSON — See the parsed JSON equivalent instantly
  • Tree View — Explore nested objects and arrays visually
  • Statistics — Get a breakdown of keys, values, arrays, objects, scalars, and nulls

Keywords

yaml formatter, yaml validator, yaml beautifier, yaml to json, yaml pretty print, yaml lint, yaml parser, yaml checker, yaml cleaner, yaml minifier, online yaml formatter, format yaml online, validate yaml online, yaml to json online

How it works

This tool runs 100% in your browser — no data is sent to any server. Here's what happens when you click Validate & Format:

Step 1 — Tokenization

Your raw YAML string is split into individual lines. Each line is analyzed for:

  • Indentation level (leading spaces)
  • Whether it's a comment (#), document separator (---), empty line, array item (-), or key-value pair

Step 2 — Parsing

A custom recursive-descent parser builds a JavaScript object from the tokens. It handles:

  • Scalars — strings, numbers, booleans, null
  • Arrays — list items with proper nesting
  • Objects — key-value maps with unlimited nesting
  • Multi-document — --- separators create an array of documents

If parsing fails, the exact error (with line number) is caught and displayed.

Step 3 — Validation

Beyond parse errors, the validator checks for common YAML mistakes:

  • Inconsistent indentation (e.g., mixing 2 and 4 spaces)
  • Unclosed single or double quotes
  • List items without a parent key
  • Colons followed by non-indented content (likely a block scalar mistake)

All errors are reported with line and column numbers.

Step 4 — Formatting

The parsed object is converted back to a YAML string using configurable options:

  • Indent — 2 or 4 spaces per level
  • Quote style — auto, single ('), or double (")
  • Sort keys — alphabetically sort object keys

Step 5 — Tree & JSON

  • The parsed object is rendered as a collapsible tree view so you can explore nested structures
  • A JSON preview is generated via JSON.stringify() for easy copying

Step 6 — Statistics

The tool counts:

  • Total lines, documents, keys, values
  • Number of objects, arrays, scalars, nulls

All results are available for one-click copy.

Examples

Beautify messy YAML

Paste unformatted or minified YAML and get clean, consistently indented output.

name:John Doe
age:30
address:
street:123 Main St
city:Boston
zip:02101
name: John Doe
age: 30
address:
  street: 123 Main St
  city: Boston
  zip: 02101

Validate YAML with line-numbered errors

Instantly detect indentation issues, unclosed quotes, and structural problems with exact line numbers.

key: value
  bad: indent
list:
- item1
- item2
  extra: space
Line 2, Col 1 — Inconsistent indentation (expected multiple of 2 spaces, got 4).

Convert YAML to JSON

Transform any valid YAML document into formatted JSON with one click.

server:
  host: localhost
  port: 8080
  ssl: true
features:
  - logging
  - auth
{
  "server": {
    "host": "localhost",
    "port": 8080,
    "ssl": true
  },
  "features": [
    "logging",
    "auth"
  ]
}

Multi-document YAML with tree view

Process YAML files with multiple documents separated by --- and explore the structure visually.

---
name: App One
version: 1.0
---
name: App Two
version: 2.0
name: App One
version: 1.0
---
name: App Two
version: 2.0

Frequently asked questions

What is a YAML formatter?

A YAML formatter (also called a YAML beautifier or pretty printer) takes messy, minified, or inconsistently indented YAML and converts it into a clean, readable format with consistent spacing and indentation.

How do I validate YAML online?

Paste your YAML into this tool and click Validate & Format. It will instantly detect errors like bad indentation, unclosed quotes, and structural issues — each with the exact line and column number so you can fix them fast.

Can I convert YAML to JSON with this tool?

Yes. After validating, the tool shows a JSON Preview of the parsed YAML. Click the copy button to grab the JSON string. It supports nested objects, arrays, booleans, numbers, nulls, and strings.

Does this tool support multi-document YAML files?

Yes. If your YAML contains multiple documents separated by ---, the tool processes all of them. You'll see the document count in the statistics panel and each document is formatted separately in the output.

Is my YAML data uploaded to a server?

No. This tool runs 100% client-side in your browser. Your YAML never leaves your device. There are no network calls, no backend, and no data storage.

What YAML features does this formatter support?

It supports scalars (strings, numbers, booleans, null), arrays, nested objects, multi-document YAML (---), and configurable formatting options (2/4 space indent, quote style, key sorting). Block scalars (| and >) are parsed but displayed as plain text in the tree view.

Why is my YAML showing a validation error?

Common causes:

  • Inconsistent indentation — mixing spaces and tabs, or using 2 spaces in one place and 4 in another
  • Unclosed quotes — a ' or " without a matching closing quote on the same line
  • List item without parent — a - item that isn't indented under a key
  • Colon without value — a key ending in : where the next line isn't indented (likely a block scalar) The error message tells you the exact line and column.

Can I sort keys alphabetically?

Yes. Toggle the Sort keys button before formatting. This will alphabetically sort all object keys in the output, which is useful for version control diffs and consistent configs.

What's the difference between this and yamllint?

yamllint This Tool
Runs in browser ❌ (CLI only) ✅
Line-numbered errors ✅ ✅
Tree view ❌ ✅
YAML → JSON ❌ ✅
Multi-document ✅ ✅
Copy to clipboard ❌ ✅
Zero install ❌ ✅

Is this tool free to use?

Yes, completely free. No sign-up and no limits. It's an open-source browser-based utility.

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