YAML

Type Coercion Traps

• yes, no, on, off, true, false → boolean; quote if literal string: "yes"
• NO (Norway country code) → false in YAML 1.1; always quote country codes
• 1.0 → float, 1 → int; quote version numbers: "1.0"
• 010 → octal (8) in YAML 1.1; quote or use 0o10 explicitly
• null, ~, empty value → null; quote if literal: "null", "~"
• .inf, -.inf, .nan → special floats; quote if literal strings

Indentation

• Spaces only—tabs are forbidden and cause parse errors
• Consistent indent width required within document—2 spaces conventional
• Sequence items - count as indentation—nested content aligns after the space

Strings

• Colon followed by space : triggers key-value—quote strings containing :
• # starts comment unless quoted—quote strings with #
• Leading/trailing spaces stripped from unquoted strings—quote to preserve
• Quote strings starting with @, `, *, &, !, |, >, {, [, %

Multiline Strings

• | literal block preserves newlines; > folded block joins lines with spaces
• Trailing newline: |- and >- strip final newline; |+ and >+ keep trailing blank lines
• Indentation of first content line sets the block indent—be consistent

Structure

• Duplicate keys: YAML spec says last wins, but some parsers error—avoid duplicates
• Anchors &name and aliases *name reduce repetition—but aliases can't override anchor values
• Document separator --- starts new document; ... ends document—useful in streams
• Empty documents between --- markers are valid but often unintended

Comments

• # only valid at line start or after whitespace—key:value#comment has no comment
• No inline comments after multiline block scalars—comment applies to next line
• No multi-line comment syntax—each line needs #

Compatibility

• YAML 1.1 vs 1.2: boolean words (yes/no), octal syntax differ—know which version parser uses
• JSON is valid YAML 1.2—but YAML features (anchors, multiline) don't round-trip to JSON
• Some parsers limit nesting depth or file size—test with expected data scale