YAML Cheatsheet – Complete Syntax Reference

Basics Start here

Structure rules

# Comments start with #
# Indentation uses SPACES only — never tabs
# YAML is case-sensitive
# Strings don't require quotes (usually)
# --- marks the start of a document
# ... marks the end of a document

⚠️ YAML uses spaces only for indentation. Tab characters will cause a parse error.

Scalars Values

Strings

unquoted: Hello World
single_quoted: 'It''s a test'
double_quoted: "Line 1\nLine 2"
with_colon: "value: with colon"
with_hash: "value # not a comment"

Numbers & Booleans

integer: 42
negative: -17
float: 3.14
scientific: 1.5e10
bool_true: true
bool_false: false
null_value: null
also_null: ~

Lists Sequences

Block style (recommended)

fruits:
  - apple
  - banana
  - cherry

ports:
  - 80
  - 443
  - 8080

Inline (flow) style

fruits: [apple, banana, cherry]

matrix:
  - [1, 2, 3]
  - [4, 5, 6]

empty_list: []

Maps Mappings

Block style

server:
  host: localhost
  port: 8080
  tls: true

Inline (flow) style

server: {host: localhost, port: 8080}

empty_map: {}

Multi-line Strings Block scalars

Literal block ( | ) — preserves newlines

message: |
  Line one
  Line two
  Line three
# Result: "Line one\nLine two\nLine three\n"

Folded block ( > ) — newlines become spaces

description: >
  This is a long sentence
  that wraps across lines
  in the source file.
# Result: "This is a long sentence that wraps..."

Strip trailing newline ( |- )

script: |-
  echo "hello"
  echo "world"
# No trailing newline at end

Keep extra newlines ( |+ )

text: |+
  Hello


# Keeps all trailing blank lines

Data Types Reference

Type	Example	Notes
String	`name: Alice`	Quotes optional unless special chars present
Integer	`port: 8080`	Decimal, hex (`0xFF`), octal (`0o77`)
Float	`ratio: 0.95`	Also `.inf`, `-.inf`, `.nan`
Boolean	`enabled: true`	`true`/`false` (lowercase in YAML 1.2)
Null	`value: null`	Also `~` or empty value
Date	`date: 2024-01-15`	ISO 8601 format
Datetime	`ts: 2024-01-15T10:00:00Z`	With timezone
Binary	`data: !!binary \|`	Base64 encoded
Force string	`zip: "01234"`	Quote to prevent type coercion

💡 Use quotes around values like "true", "null", "1.0", or "01234" when you need them treated as strings, not their native types.

Anchors & Aliases DRY configs

Define & reuse with & and *

defaults: &defaults
  timeout: 30
  retries: 3
  log_level: info

production:
  <<: *defaults
  log_level: warn  # override

staging:
  <<: *defaults
  timeout: 60    # override

Reuse a scalar value

image_tag: &tag v1.4.2

services:
  api:
    image: myapp/api:*tag
  worker:
    image: myapp/worker:*tag

Nested Structures Real-world

List of maps (common in K8s, CI configs)

steps:
  - name: Checkout
    uses: actions/checkout@v4
  - name: Build
    run: npm run build
    env:
      NODE_ENV: production
  - name: Test
    run: npm test

Special Characters Quoting guide

Character	Context	Fix
`:`	In a value	Quote the value: `"host:port"`
`#`	Inline in value	Quote it: `"color #fff"`
`@`, `	Start of value	Always quote
`{`, `[`	Start of value	Quote or use block style
`*`, `&`	Start of value	Quote to avoid anchor/alias parsing
`\|`, `>`	Start of value	Quote to avoid block scalar
`!`	Start of value	Quote (used for type tags)

Multi-document Files Advanced

Separate documents with ---

---  # Document 1: Deployment
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
---  # Document 2: Service
apiVersion: v1
kind: Service
metadata:
  name: my-app-svc