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YAML Cheatsheet

Quick reference for YAML syntax.

Basic Structures

# Simple mapping (key: value)
name: John
age: 30
city: New York

# Simple sequence (list)
- apple
- banana
- carrot

# Nested structures
person:
  name: John
  age: 30
  hobbies:
    - reading
    - coding
    - hiking

Scalars

# Plain (unquoted)
title: Hello World

# Single quoted (literal, no escaping)
message: 'It''s a nice day'

# Double quoted (allows escaping)
path: "C:\\Windows\\System32"

# Multi-line literal (preserves newlines)
poem: |
  Roses are red
  Violets are blue
  YAML is great
  And so are you

# Multi-line folded (joins lines)
description: >
  This is a long paragraph
  that will be folded into
  a single line with spaces.

# Integer
count: 42

# Float
price: 19.99

# Scientific notation
avogadro: 6.022e23

# Hexadecimal
hex: 0x1A

# Octal
octal: 0o12

# Boolean values
enabled: true
disabled: false

# Null values
nothing: null
nothing: ~
nothing:  # empty value = null

Collections

# Flow mapping (JSON-like)
person: {name: John, age: 30}

# Flow sequence (JSON-like)
colors: [red, green, blue]

# Mixed
people: [
  {name: Alice, age: 25},
  {name: Bob, age: 30}
]

# Block mapping
person:
  name: John
  age: 30
  address:
    street: 123 Main St
    city: New York

# Block sequence
colors:
  - red
  - green
  - blue

# Mapping with complex keys
? - key1
  - key2
: value for complex key

# Or use explicit key indicator
? complex key
: value

Anchors & Aliases

# Define anchor with &
defaults: &defaults
  timeout: 30
  retries: 3
  log_level: info

# Reference with *
production:
  <<: *defaults
  host: prod.example.com

staging:
  <<: *defaults
  host: staging.example.com
  log_level: debug  # Override

Documents

# Single document (no markers needed)
name: value
list:
  - item1
  - item2

# Document 1
---
name: Document 1
type: config

# Document 2
---
name: Document 2
type: data

%YAML 1.2
---
# Document content
name: value
...

Comments

# Full line comment
name: value  # Inline comment

# Comments can go anywhere
person:
  # name: old_value  # Commented out
  name: new_value

Tags

# Explicit type tags
number: !!int 42
text: !!str 42
binary: !!binary SGVsbG8gV29ybGQ=

# Custom tags
date: !date 2025-12-10
config: !include config.yaml

Common Patterns

# Application config
app:
  name: MyApp
  version: 1.0.0
  debug: false

database:
  host: localhost
  port: 5432
  name: myapp_db
  credentials:
    username: admin
    password: secret

features:
  - authentication
  - api
  - admin_panel

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.14.2
    ports:
    - containerPort: 80

version: '3'
services:
  web:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./html:/usr/share/nginx/html
  db:
    image: postgres:13
    environment:
      POSTGRES_PASSWORD: secret

Tips & Gotchas

Indentation

  • Use spaces only, not tabs
  • Be consistent with indentation (usually 2 or 4 spaces)
  • Indentation determines structure

Quotes

  • Usually optional for simple strings
  • Required for: strings starting with special chars, reserved words (yes, no, true, false), numbers as strings
  • Example: version: "2" not version: 2

Reserved Words

These are interpreted as booleans/null unless quoted: 

# Interpreted as boolean true:
answer: yes
# String "yes":
answer: "yes"
Reserved: yes, no, true, false, on, off, null, ~

Timestamps

YAML 1.1 auto-converts timestamp-like strings: 

# May be interpreted as date in YAML 1.1:
version: 2020-10-01
# Safe:
version: "2020-10-01"

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