YAML Formatter & Validator - Format YAML Online

Free YAML formatter, validator and linter. Format, lint, validate and convert YAML files directly in your browser.

Input YAML

Output

Paste your YAML here...

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What is YAML?

YAML (YAML Ain't Markup Language) is a human-readable data serialization language. It is commonly used for configuration files, data exchange between languages, and in applications where data is being stored or transmitted. YAML's syntax is designed to be easy to read and write, using indentation to represent data structure, making it popular in DevOps, CI/CD pipelines (GitHub Actions, GitLab CI), Docker Compose, Kubernetes, and Ansible.

YAML vs JSON

Both YAML and JSON are data serialization formats, but they serve different purposes. YAML prioritizes human readability with a minimal syntax using indentation — it supports comments, anchors, and complex data types. JSON is more machine-oriented with strict syntax using braces and brackets — it's the standard for web APIs and has faster parsing. YAML is a superset of JSON, meaning any valid JSON is also valid YAML. Our tool lets you convert between both formats seamlessly.

YAML Examples

Basic YAML

name: John Doe
age: 30
active: true
skills:
  - Python
  - JavaScript
  - DevOps

Docker Compose

version: '3.8'
services:
  web:
    image: nginx:latest
    ports:
      - 8080:80
    volumes:
      - ./app:/usr/share/nginx/html

YAML Syntax Guide

Key-Value Pairs

Basic structure: key: value. Strings do not require quotes unless they contain special characters.

Lists

Use - prefix for list items. Each item can be any YAML type including nested objects.

Nested Objects

Use indentation (2 or 4 spaces) to represent nested structures. Consistent indentation is required.

Comments

Use # for comments. YAML supports inline and block comments.

How to Use YAML Formatter

1
Paste your YAML content into the input editor
2
Click "Format" to beautify or "Validate" to check for errors
3
Use "YAML to JSON" or "JSON to YAML" to convert between formats
4
Copy the formatted output or download it as a file

Frequently Asked Questions

What is YAML used for?

YAML is primarily used for configuration files in software development and DevOps. Common use cases include Docker Compose files, Kubernetes manifests, CI/CD pipeline definitions (GitHub Actions, GitLab CI), Ansible playbooks, and application configuration. YAML's readability makes it ideal for files that developers and operators need to read and edit manually.

Is it safe to validate YAML online?

Yes. Our YAML validator runs entirely in your browser using JavaScript. Your YAML data never leaves your device — we do not upload, store, or share any data. All parsing, validation, and conversion happens locally on your machine.

Can YAML be converted to JSON?

Yes. YAML is a superset of JSON, meaning any JSON document is valid YAML, and most YAML can be converted to JSON. Our tool provides one-click conversion between YAML and JSON in both directions. Note that some YAML-specific features like anchors and aliases may not have a direct JSON equivalent.

What are common YAML errors?

Common YAML errors include: inconsistent indentation (mixing tabs and spaces), using tabs instead of spaces, missing colons after keys, incorrect list formatting, and unquoted strings that look like other YAML types (like 'true', 'false', 'null', or numbers). Our validator catches these errors and shows you exactly where they occur.

How do I format or validate a Docker Compose file?

Paste your docker-compose.yml into the input editor and click Validate to check the YAML syntax, then Format to clean up the indentation. Note that this tool checks YAML syntax only — it does not validate Docker-specific semantics such as image names or port ranges.

What are YAML anchors and aliases?

Anchors (&name) mark a block of YAML so it can be reused later with an alias (*name). They are a built-in way to avoid repetition — for example, defining one default settings block and referencing it from several services. Anchors and aliases are a YAML-only feature with no direct JSON equivalent, which is why converting anchored YAML to JSON expands the reused content.

YAML vs TOML — which format should I use?

YAML is more flexible and widely used in DevOps tooling (Docker Compose, Kubernetes, Ansible, GitHub Actions). TOML is stricter and simpler, designed for configuration files in ecosystems like Rust (Cargo.toml) and Python (pyproject.toml). If humans will hand-edit the file, YAML is usually more pleasant; for simple key-value configuration with little nesting, TOML is a solid choice.

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