YAML Cheat Sheet

Q: Can I use tabs in YAML?

Not for indentation — YAML only allows spaces there, and a tab is a parse error. Tabs are fine inside quoted strings.

Q: What is the difference between | and > in YAML?

| (literal) keeps every line break. > (folded) joins lines with spaces and keeps only blank-line breaks. Add - to drop the final newline: |-.

Q: Why did my value turn into true or false?

Older YAML 1.1 parsers read words like yes, no, on, off and NO as booleans. Quote the value to keep it as text.

Q: What do --- and ... mean?

--- starts a new document, so one file can hold several. ... ends a document without starting a new one.

The syntax you need for config files, how each value is parsed, multi-line strings, anchors, and the gotchas that turn NO into false.

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Updated 28 October 2026

Format and validate YAML with line numbers, or convert between YAML and JSON.

Open the YAML formatter

YAML basics

# A comment
name: Alice            # key: value (a space after the colon)
age: 30
address:               # nested map: indent with spaces, never tabs
  city: London
  zip: "SW1A 1AA"
roles:                 # list
  - admin
  - editor
inline_map: {a: 1, b: 2}
inline_list: [x, y, z]

Indent with spaces only. A tab in the indentation is an error.
Put a space after the colon: key: value. key:value is one string.
Items at the same level must line up exactly. Two spaces per level is the usual style.
YAML 1.2 is a superset of JSON, so any JSON document is also valid YAML.

Try ↗ buttons below open the example in the YAML formatter, which shows how it is parsed.

Values and how they are parsed

Type	YAML	Parsed as
Plain string	`title: Hello world`	"Hello world"	Try ↗
Single-quoted	`s: 'it''s'`	"it's" — '' is a literal quote; no escapes	Try ↗
Double-quoted	`s: "tab\there"`	Escapes like \n, \t and \u00e9 work	Try ↗
Integer	`n: 42`	42	Try ↗
Float	`n: 3.14`	3.14	Try ↗
Hex / octal	`n: 0x1F`	31. Octal in YAML 1.2 is 0o755	Try ↗
Infinity / NaN	`n: .inf`	Infinity (also -.inf and .nan)	Try ↗
Boolean	`ok: true`	true / false	Try ↗
Null	`v: ~`	null — also null or an empty value	Try ↗
Date	`d: 2026-10-28`	A date in js-yaml and PyYAML; quote it to keep a string	Try ↗

Multi-line strings: | and >

Style	YAML	Value
Literal — keeps line breaks	`t: \|` `line1` `line2`	`"line1\nline2\n"`
Literal, no final newline	`t: \|-` `line1` `line2`	`"line1\nline2"`
Folded — joins lines with spaces	`t: >` `line1` `line2`	`"line1 line2\n"`
Keep all trailing newlines	`t: \|+`	Like `\|` but trailing blank lines are kept

A blank line inside folded text (>) becomes a line break. Use | for scripts, certificates and anything where line breaks matter.

Anchors, aliases and merge keys

defaults: &defaults      # & names this node
  adapter: postgres
  pool: 5

development:
  <<: *defaults          # * reuses it; << merges its keys in
  database: dev_db

test:
  <<: *defaults
  pool: 2                # keys you set win over merged ones

<< merge keys come from YAML 1.1. js-yaml, PyYAML and most config tools support them, but they are not part of the YAML 1.2 core schema.

Multiple documents in one file

One file can hold several documents separated by ---. Kubernetes manifests use this to put several resources in one file. ... marks the end of a document and is rarely needed.

kind: Service
metadata:
  name: web
---
kind: Deployment
metadata:
  name: web

The YAML formatter handles multi-document files; YAML → JSON turns them into a JSON array.

YAML gotchas

Problem	Example	What happens	Fix
The Norway problem	`country: NO`	YAML 1.1 parsers such as PyYAML read `NO`, `yes`, `on` and `off` as booleans. YAML 1.2 parsers such as js-yaml keep them as strings	Quote it: `country: "NO"`
Version numbers	`version: 1.10`	Parsed as the number 1.1	Quote it: `version: "1.10"`
Leading zeros	`mode: 0755`	Octal 493 in YAML 1.1, decimal 755 in YAML 1.2	Quote it, or write `0o755`
Colon in a value	`title: Note: read me`	Error: a second key on the same line	Quote the value
Special first character	`ref: *main`	Strings starting with * & ! @ ` % \| have special meanings	Quote the value
Tabs	A tab before `key:`	Error — tabs are not allowed for indentation	Indent with spaces
Duplicate keys	`a: 1` … `a: 2`	An error in js-yaml; other parsers silently keep the last one	Remove the duplicate
Dates	`released: 2026-10-28`	Becomes a date object, not a string	Quote it if you need the text

YAML in code

Language	Read YAML	Write YAML
Python (PyYAML)	`yaml.safe_load(text)`	`yaml.safe_dump(data, sort_keys=False)`
JavaScript (js-yaml)	`yaml.load(text)`	`yaml.dump(data)`
Go (yaml.v3)	`yaml.Unmarshal(data, &v)`	`yaml.Marshal(v)`
Java (SnakeYAML)	`new Yaml().load(text)`	`new Yaml().dump(data)`
Ruby	`YAML.safe_load(text)`	`data.to_yaml`
Command line (yq)	`yq '.spec.replicas' deploy.yaml`	`yq -o=json deploy.yaml` (to JSON)

Use the safe loaders (safe_load, js-yaml's default load) for anything you didn't write yourself — full loaders can create arbitrary objects.

Frequently asked questions

Can I use tabs in YAML?

Not for indentation — YAML only allows spaces there, and a tab is a parse error. Tabs are fine inside quoted strings.

What is the difference between | and > in YAML?

| (literal) keeps every line break. > (folded) joins lines with spaces and keeps only blank-line breaks. Add - to drop the final newline: |-.

Why did my value turn into true or false?

Older YAML 1.1 parsers read words like yes, no, on, off and NO as booleans. Quote the value to keep it as text.

Is JSON valid YAML?

Yes, in YAML 1.2: every JSON document is a valid YAML document. The JSON → YAML converter turns JSON into the more readable block style.

What do --- and ... mean?

--- starts a new document, so one file can hold several. ... ends a document without starting a new one.