YAML Cheat Sheet

Everything you need to know about YAML syntax — scalars, sequences, mappings, multi-line strings, anchors, and the type coercion gotchas that catch everyone.

Last updated: May 21, 2026

Scalars (Values)

YAML	Type	JSON equivalent
name: Alice	String (bare)	"name": "Alice"
name: "Alice"	String (quoted)	"name": "Alice"
name: 'Alice'	String (single-quoted)	"name": "Alice"
age: 30	Integer	"age": 30
price: 9.99	Float	"price": 9.99
active: true	Boolean (true)	"active": true
active: false	Boolean (false)	"active": false
value: null	Null	"value": null
value: ~	Null (tilde shorthand)	"value": null
count: 1e3	Scientific notation	"count": 1000
hex: 0xFF	Hex integer (YAML 1.1)	"hex": 255

Mappings (Objects)

# Block style (most readable)
server:
  host: localhost
  port: 3000
  debug: true

# Flow style (inline, like JSON)
server: {host: localhost, port: 3000, debug: true}

Keys and values separated by : (colon + space). Nesting via indentation (2 spaces recommended).

Sequences (Arrays)

# Block style
tags:
  - admin
  - editor
  - user

# Flow style (inline)
tags: [admin, editor, user]

# Array of objects
users:
  - name: Alice
    role: admin
  - name: Bob
    role: user

Multi-line Strings

Indicator	Behaviour	Result
\| (literal block)	Preserves newlines exactly	Line breaks kept as-is
> (folded block)	Folds newlines into spaces	Becomes a single paragraph
\|- (strip)	Literal, no trailing newline	Final newline removed
\|+ (keep)	Literal, keep all trailing newlines	Trailing newlines preserved

# Literal block — newlines preserved
description: |
  Line one.
  Line two.
  Line three.

# Folded block — newlines become spaces
summary: >
  This long text will be
  folded into one line.

Anchors & Aliases

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

# Reuse with * alias
production:
  <<: *defaults   # merge — overrides defaults
  host: prod.example.com

staging:
  <<: *defaults
  host: staging.example.com

&name defines an anchor. *name references it. <<: *name merges the anchor's keys.

Type Coercion Gotchas (YAML 1.1)

YAML value	Parsed as	Fix
yes / no	true / false	Quote: "yes"
on / off	true / false	Quote: "on"
True / False / TRUE	boolean	Quote if string intended
Null / NULL	null	Quote if string intended
1.0	float 1.0	Use !!str to force string
0755	Octal 493 (YAML 1.1)	Quote: "0755"
1_000_000	Integer 1000000	Numeric separator — use quotes if string
2001-01-23	Date object	Quote: "2001-01-23" for string

Special Syntax

# CommentComments — from # to end of line. YAML natively supports comments.

---Document start marker. Separates multiple documents in one file.

...Document end marker.

!!str, !!int, !!boolExplicit type tags to override auto-detection.

|, >Multi-line string indicators (literal and folded).

&anchor / *aliasDefine and reference reusable nodes.

{}, []Flow-style (inline) mapping and sequence.

? keyExplicit complex key syntax.

YAML vs JSON Quick Comparison

Feature	YAML	JSON
Comments	Yes (#)	No
Trailing commas	N/A	Not allowed
String quotes	Optional (bare strings ok)	Required (double only)
Multiline strings	Yes (\| and >)	Only via \n escape
Anchors/aliases	Yes	No
Data types	6 + dates, binary…	6 (string/number/bool/null/array/object)
File extension	.yaml or .yml	.json
Whitespace	Significant (indentation)	Ignored

Client-Side Processing

Input Data Stays on Device

Instant Local Execution

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What is YAML Cheat Sheet?

YAML (YAML Ain't Markup Language) is a human-friendly data serialization format used extensively for configuration files (Docker Compose, GitHub Actions, Kubernetes, Ansible, etc.). It uses indentation for structure instead of brackets, making it readable but sensitive to whitespace.

This cheat sheet covers all YAML syntax: scalar types and their auto-detection, block and flow styles, multi-line string blocks, anchors (`&`) and aliases (`*`), and the notorious type coercion pitfalls that cause unexpected parse results.

How to Use YAML Cheat Sheet

Browse the sections or use Ctrl+F to find a specific topic. Each entry shows the YAML syntax with a description and the equivalent JSON value. For validation, use the YAML Validator tool.

Common Use Cases

DevOps engineers writing Kubernetes manifests, Docker Compose, or Ansible playbooks.
Developers configuring GitHub Actions workflows who need YAML syntax reminders.
Students learning YAML who want a structured reference alongside JSON.
Engineers debugging YAML parse errors caused by indentation or type coercion.

Example Input and Output

YAML mapping demonstrating key scalar types and sequences.

YAML

name: Alice
age: 30
active: true
tags:
  - admin
  - user
address:
  city: London

Equivalent JSON

{"name":"Alice","age":30,"active":true,"tags":["admin","user"],"address":{"city":"London"}}

Tip: use a validator

YAML indentation errors are hard to spot visually. Paste your YAML into the YAML Validator to get the exact line of the parse error.

Frequently Asked Questions

Why does "yes" become true in YAML?

YAML 1.1 (used by many parsers) auto-converts yes, no, on, off, true, false (and their capitalised variants) to booleans. YAML 1.2 only treats true/false as booleans. Quote the string to prevent coercion: "yes".

What is the difference between | and > in multi-line strings?

| (literal block) preserves newlines exactly. > (folded block) folds newlines into spaces (like word-wrap), making the string a single line. Both preserve a trailing newline by default.

Can YAML have comments?

Yes — YAML supports comments with #. Unlike JSON, YAML comments are official syntax and are ignored by parsers.

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