Scalars

A scalar is a single value: string, number, boolean, null.

string: hello
number: 42
float: 3.14
boolean: true
null_value: null

Type inference (YAML's footgun):

• true, True, TRUE, yes, Yes, on, On → boolean true (YAML 1.1).
• false, no, off → boolean false.
• null, Null, NULL, ~, empty → null.
• 42 → integer.
• 3.14 → float.
• 0xff → 255 (hex).
• 0o17 → 15 (octal in YAML 1.2).
• 2024-01-01 → date.
• Anything else → string.

YAML 1.1's "Norway problem": country code NO → boolean false. Caused real bugs.

YAML 1.2 (preferred): only true, false, null are special. Others are strings.

To force string: quote it.

string: hello       # string
quoted: "true"      # string "true"
real_bool: true     # boolean
zip: "01234"        # string (without quotes, leading 0 → octal in 1.1)

Quoting:

• Single quotes: '...'. No escapes; '' for embedded '.
• Double quotes: "...". JSON-style escapes (\n, \", \u00ff).

escaped: "first\nsecond"
literal: 'first\nsecond'    # backslash-n LITERAL, no newline

Multi-line strings:

• Literal block (|): preserve newlines.
• Folded block (>): join lines with spaces; blank lines stay.

literal: |
  line 1
  line 2
  line 3

folded: >
  these lines
  will be joined
  with spaces.

  Blank line stays.

Result:

• literal: "line 1\nline 2\nline 3\n".
• folded: "these lines will be joined with spaces.\nBlank line stays.\n".

Modifiers:

• |+ keep trailing newlines.
• |- strip trailing newlines.
• >- strip + fold.