YAML — YAML Ain't Markup Language

Reference & Beautifier

# Strings — bare or quoted
name:        Ada Lovelace
title:       "Countess of Computing"
bio: |
  First programmer.
  Wrote the algorithm.

# Numbers, booleans, null
age:         36
pi:          3.14159
active:      true
nickname:    null

# Sequence (list)
scores:
  - 98
  - 100
  - 87

# Nested mapping (object)
address:
  city:      London
  postcode:  W1A 1AA

# Anchors & aliases
defaults: &defaults
  timeout: 30
production:
  <<: *defaults
  timeout: 60

key: — mapping key string — text value 42 — number true/false — boolean null — nothing &anchor *alias — reuse # comment — ignored

string

bare · "quoted" · 'single'

Bare words are strings. Quote when special chars needed.

number

42 · -7 · 3.14 · 1e6

Integer or float. Written without quotes.

boolean

true · false · yes · no

true/false (also yes/no, on/off in YAML 1.1).

null

null · ~ · (empty)

Explicit absence of value. Tilde ~ is shorthand.

mapping

key: value

Key–value pairs. Keys end with a colon and space.

sequence

- item1 - item2

Ordered list. Each item prefixed with "- ".

block scalar

key: | line one line two

| preserves newlines. > folds them into spaces.

anchor/alias

&name · *name · <<:

Define once with &, reuse with *. Merge maps with <<:.