Three files: examples.md, yaml-cheatsheet.md and yaml-cheatsheet.yml

examples.md

adapted from this blog

# YAML
name: Jon

# YAML
object:
  attributes:
    - attr1
    - attr2
    - attr3
  methods: [ getter, setter ]

parses to this json

{"object": {"attributes": ["attr1", "attr2", "attr3"], ...

# YAML
sonnet: |
  I wish I could
  write a poem
  but I can"t

parses to:

{"sonnet": "I wish I could\nwrite a poem\nbut I can't\n"}

# YAML
---
document: this is doc 1
---
document: this is doc 2
...

name: SomeObject
attributes:
  - attr1
  - attr2
  - attr3
methods: [ getter, setter ]
---
name: MyPrettyObject
attributes:
  - attr1
  - attr2
  - attr3
methods: [ getter, setter ]

parses to:

{"attributes": ["attr1", "attr2", "attr3"],
 "methods": ["getter", "setter"],
 "name": "SomeObject"}
{"attributes": ["attr1", "attr2", "attr3"],
 "methods": ["getter", "setter"],
 "name": "MyPrettyObject"}

YAML also supports variables, or repeated nodes. The simplest explanation is that you define something as a variable by preceding it with "&NAME value" and you can refer to it with "*NAME" e.g.:

# YAML
some_thing: &NAME foobar
other_thing: *NAME

Parses to:

{"other_thing": "foobar", "some_thing": "foobar"}

yaml-cheatsheet.md

YAML 1.1: Reference card

---

Collection indicators:

    '? ' : Key indicator.
    ': ' : Value indicator.
    '- ' : Nested series entry indicator.
    ', ' : Separate in-line branch entries.
    '[]' : Surround in-line series branch.
    '{}' : Surround in-line keyed branch.

Scalar indicators:

    '''' : Surround in-line unescaped scalar ('' escaped ').
    '"'  : Surround in-line escaped scalar (see escape codes below).
    '|'  : Block scalar indicator.
    '>'  : Folded scalar indicator.
    '-'  : Strip chomp modifier ('|-' or '>-').
    '+'  : Keep chomp modifier ('|+' or '>+').
    1-9  : Explicit indentation modifier ('|1' or '>2').
           # Modifiers can be combined ('|2-', '>+1').

Alias indicators:

    '&'  : Anchor property.
    '*'  : Alias indicator.

Tag property: # Usually unspecified.

    none    : Unspecified tag (automatically resolved by application).
    '!'     : Non-specific tag (by default, "!!map"/"!!seq"/"!!str").
    '!foo'  : Primary (by convention, means a local "!foo" tag).
    '!!foo' : Secondary (by convention, means "tag:yaml.org,2002:foo").
    '!h!foo': Requires "%TAG !h! <prefix>" (and then means "<prefix>foo").
    '!<foo>': Verbatim tag (always means "foo").

Document indicators:

    '%'  : Directive indicator.
    '---': Document header.
    '...': Document terminator.

Misc indicators:

    ' #' : Throwaway comment indicator.
    '`@' : Both reserved for future use.

Special keys:

    '='  : Default "value" mapping key.
    '<<' : Merge keys from another mapping.

Core types: # Default automatic tags.

    '!!map' : { Hash table, dictionary, mapping }
    '!!seq' : { List, array, tuple, vector, sequence }
    '!!str' : Unicode string

More types:

    '!!set' : { cherries, plums, apples }
    '!!omap': [ one: 1, two: 2 ]

Language Independent Scalar types:

    { ~, null }              : Null (no value).
    [ 1234, 0x4D2, 02333 ]   : [ Decimal int, Hexadecimal int, Octal int ]
    [ 1_230.15, 12.3015e+02 ]: [ Fixed float, Exponential float ]
    [ .inf, -.Inf, .NAN ]    : [ Infinity (float), Negative, Not a number ]
    { Y, true, Yes, ON  }    : Boolean true
    { n, FALSE, No, off }    : Boolean false
    ? !!binary >
        R0lG...BADS=
    : >-
        Base 64 binary value.

Escape codes:

 Numeric   : { "\x12": 8-bit, "\u1234": 16-bit, "\U00102030": 32-bit }
 Protective: { "\\": '\', "\"": '"', "\ ": ' ', "\<TAB>": TAB }
 C         : { "\0": NUL, "\a": BEL, "\b": BS, "\f": FF, "\n": LF, "\r": CR,
               "\t": TAB, "\v": VTAB }
 Additional: { "\e": ESC, "\_": NBSP, "\N": NEL, "\L": LS, "\P": PS }

yaml-cheatsheet.yml

%YAML 1.1   # Reference card
---
Collection indicators:
    '? ' : Key indicator.
    ': ' : Value indicator.
    '- ' : Nested series entry indicator.
    ', ' : Separate in-line branch entries.
    '[]' : Surround in-line series branch.
    '{}' : Surround in-line keyed branch.
Scalar indicators:
    '''' : Surround in-line unescaped scalar ('' escaped ').
    '"'  : Surround in-line escaped scalar (see escape codes below).
    '|'  : Block scalar indicator.
    '>'  : Folded scalar indicator.
    '-'  : Strip chomp modifier ('|-' or '>-').
    '+'  : Keep chomp modifier ('|+' or '>+').
    1-9  : Explicit indentation modifier ('|1' or '>2').
           # Modifiers can be combined ('|2-', '>+1').
Alias indicators:
    '&'  : Anchor property.
    '*'  : Alias indicator.
Tag property: # Usually unspecified.
    none    : Unspecified tag (automatically resolved by application).
    '!'     : Non-specific tag (by default, "!!map"/"!!seq"/"!!str").
    '!foo'  : Primary (by convention, means a local "!foo" tag).
    '!!foo' : Secondary (by convention, means "tag:yaml.org,2002:foo").
    '!h!foo': Requires "%TAG !h! <prefix>" (and then means "<prefix>foo").
    '!<foo>': Verbatim tag (always means "foo").
Document indicators:
    '%'  : Directive indicator.
    '---': Document header.
    '...': Document terminator.
Misc indicators:
    ' #' : Throwaway comment indicator.
    '`@' : Both reserved for future use.
Special keys:
    '='  : Default "value" mapping key.
    '<<' : Merge keys from another mapping.
Core types: # Default automatic tags.
    '!!map' : { Hash table, dictionary, mapping }
    '!!seq' : { List, array, tuple, vector, sequence }
    '!!str' : Unicode string
More types:
    '!!set' : { cherries, plums, apples }
    '!!omap': [ one: 1, two: 2 ]
Language Independent Scalar types:
    { ~, null }              : Null (no value).
    [ 1234, 0x4D2, 02333 ]   : [ Decimal int, Hexadecimal int, Octal int ]
    [ 1_230.15, 12.3015e+02 ]: [ Fixed float, Exponential float ]
    [ .inf, -.Inf, .NAN ]    : [ Infinity (float), Negative, Not a number ]
    { Y, true, Yes, ON  }    : Boolean true
    { n, FALSE, No, off }    : Boolean false
    ? !!binary >
        R0lG...BADS=
    : >-
        Base 64 binary value.
Escape codes:
 Numeric   : { "\x12": 8-bit, "\u1234": 16-bit, "\U00102030": 32-bit }
 Protective: { "\\": '\', "\"": '"', "\ ": ' ', "\<TAB>": TAB }
 C         : { "\0": NUL, "\a": BEL, "\b": BS, "\f": FF, "\n": LF, "\r": CR,
               "\t": TAB, "\v": VTAB }
 Additional: { "\e": ESC, "\_": NBSP, "\N": NEL, "\L": LS, "\P": PS }