YAML Syntax Guide

YAML syntax reference: scalars, collections, anchors, multi-line strings, and comparison with JSON equivalents.

📄 Free PDF Download

Print-friendly · 1-2 pages · No sign-up required

Basic Types

Type	YAML	JSON Equivalent
`String`	`name: Alice`	`"name": "Alice"`
`Integer`	`age: 30`	`"age": 30`
`Float`	`price: 9.99`	`"price": 9.99`
`Boolean`	`active: true`	`"active": true`
`Null`	`value: null # or ~`	`"value": null`
`Sequence`	`- a - b - c`	`["a", "b", "c"]`
`Mapping`	`key: value`	`{"key": "value"}`

Collections

# Block sequence
fruits:
  - apple
  - banana
  - cherry

# Inline sequence (flow style)
fruits: [apple, banana, cherry]

# Nested mapping
address:
  street: Main St
  city: Kyiv
  zip: 01001

# Inline mapping (flow style)
address: {street: Main St, city: Kyiv}

Multi-line Strings

Operator	Name	Behaviour
`\|`	`Literal block`	`Preserves newlines`
`>`	`Folded block`	`Newlines become spaces`
`\|-`	`Literal, strip`	`No trailing newline`
`>-`	`Folded, strip`	`Folded, no trailing newline`

Anchors & Aliases

# Define anchor
defaults: &defaults
  timeout: 30
  retries: 3

# Reference alias (merges defaults)
production:
  <<: *defaults
  host: prod.example.com

development:
  <<: *defaults
  host: localhost

Common Gotchas

› Indentation: MUST use spaces, NEVER tabs
› yes/no/on/off are parsed as booleans (quote if literal)
› 123 is integer; '123' is string — quote when in doubt
› Colons in strings: must quote — title: 'Error: not found'
› YAML 1.2 (default) fixes many YAML 1.1 quirks (octal, sexagesimal)
› Multiple documents in one file: separate with ---

Keep This Reference Handy

Download the PDF and keep it on your desk or share with your team.

Download YAML Syntax Guide PDF