Format YAML,
instantly.

What is YAML?

YAML (YAML Ain't Markup Language) is a human-readable data serialization format used for configuration files. Unlike JSON, which uses braces and quotes, YAML uses indentation to express structure — making it far easier to read and write by hand. That readability is why it's the default configuration language across the DevOps ecosystem. This tool targets the YAML 1.2 specification.

Why YAML is so easy to break

YAML's readability comes at a price: it is extremely sensitive to whitespace. A tab instead of spaces, an inconsistent indentation level, or a missing space after a colon can cause a parse failure — or worse, a silent error where the parser reads your structure differently than you intended. A formatter solves this by normalizing indentation and validating syntax with precise error locations.

The basic building blocks

Scalars are simple values — strings, numbers, booleans, and null. Mappings map keys to values with colons. Sequences are ordered lists denoted by dashes.

# Scalars
name: John Doe
age: 30
enabled: true

# Mapping (key-value pairs)
person:
  name: Alice
  address:
    street: 123 Main St

# Sequence (list)
fruits:
  - apple
  - banana
  - orange

Advanced features: anchors and multi-document files

Anchors (&) mark a node for reuse and aliases (*) reference it — ideal for DRY configuration. Multi-document files hold several documents separated by ---, common in Kubernetes manifests. Tick Expand anchors in the formatter to resolve them into their full values.

# Anchors and aliases
defaults: &defaults
  timeout: 30
  retries: 3

service-a:
  <<: *defaults
  name: service-a

# Multi-document file
---
kind: Service
metadata:
  name: my-service
---
kind: Deployment
metadata:
  name: my-deployment

Multi-line strings: block scalars

YAML offers two block styles for long strings. The literal style (|) preserves every line break — use it for shell scripts, certificates, and ConfigMap data. The folded style (>) converts single line breaks into spaces — use it for long prose that should reflow. A chomping indicator (- or +) controls the final trailing newline.

# Literal (|): keep every newline
script: |
  #!/bin/bash
  echo "line 1"
  echo "line 2"

# Folded (>): single breaks become spaces
description: >
  This long description folds
  into one readable line.

# Chomping: strip or keep the final newline
folded_strip: >-   # no trailing newline
  text here
literal_keep: |+   # keep trailing blank lines
  text here

Best practices

• Always use spaces for indentation — never tabs, and never mix levels.
• Quote ambiguous strings like "true", "1.0", or version numbers to prevent type coercion.
• Use comments liberally — YAML supports # comments.
• Keep nesting shallow — deeply nested YAML is hard to read and error-prone.
• Use anchors for repeated blocks instead of copying configuration.
• Validate before committing — a YAML validator catches syntax errors before they reach production.

When to Use YAML

YAML dominates the DevOps and cloud-native ecosystem: Kubernetes manifests, Docker Compose, GitHub Actions, Ansible, OpenAPI, and Helm charts. Strengths: most human-readable for nested structures, supports comments, anchors, and multi-document files. Weaknesses: whitespace sensitivity leads to subtle bugs, and parsing is slower than JSON.

When to Use JSON

JSON is the universal data-exchange format: REST APIs, package.json, NoSQL databases, and native browser support. Strengths: fast to parse everywhere, strict unambiguous syntax, universal language support. Weaknesses: no comments, no anchors, verbose brackets and commas.

When to Use TOML

TOML (Tom's Obvious, Minimal Language) is rising in language ecosystems: Cargo.toml for Rust and pyproject.toml for Python. Strengths: clear section headers, less whitespace-sensitive, short spec. Weaknesses: awkward for deep nesting, smaller ecosystem, no anchors.

Migrating Between Formats

JSON to YAML — remove brackets, replace commas with newlines, add indentation. YAML to JSON — add brackets, commas, and quotes. YAML to TOML — map nested keys to [table] sections. YAML to XML — map keys to elements. All are one click with our YAML to JSON, YAML to TOML, YAML to XML, and JSON to YAML converters.

# JSON input
{"server": {"host": "localhost", "port": 8080}}

# YAML output
server:
  host: localhost
  port: 8080