TOML

Write valid TOML configuration files with correct types and structure.

Strings

• Basic strings "..." support escapes: \n, \t, \\, \"
• Literal strings '...' are raw—no escape sequences, backslash is literal
• Multiline basic """...""" allows newlines; leading newline after """ is trimmed
• Multiline literal '''...''' for raw blocks; no escape processing

Keys

• Bare keys: alphanumeric, dash, underscore only—key-name_1 valid
• Quoted keys for special chars: "key with spaces" or 'key.with.dots'
• Dotted keys a.b.c = 1 equivalent to nested tables—defines [a.b] implicitly
• Keys are case-sensitive—Key and key are different

Tables

• [table] defines table; all following key-values belong to it until next header
• [a.b.c] creates nested structure—parent tables created implicitly
• Dotted keys under [table] extend it: [fruit] then apple.color = "red" works
• Defining table after dotted key created it is error—order matters

Arrays of Tables

• [[array]] appends new table to array each time it appears
• [[products]] twice creates products[0] and products[1]
• Mix [array.nested] after [[array]] to add to most recent array element
• Cannot redefine static table as array or vice versa

Inline Tables

• point = { x = 1, y = 2 } for compact single-line tables
• Inline tables cannot span lines (until TOML 1.1)
• Cannot add keys to inline table after definition—immutable once closed
• Nested inline tables allowed but reduce readability

Types

• Integers: decimal, hex 0xDEAD, octal 0o755, binary 0b1010
• Underscores for readability: 1_000_000 is valid
• Floats: 3.14, 5e-10, inf, nan (case-sensitive)
• Booleans: true/false only—lowercase, no yes/no/on/off

Dates & Times

• RFC 3339 format: 2024-01-15T14:30:00Z or with offset +05:30
• Local datetime: 2024-01-15T14:30:00 (no timezone)
• Local date: 2024-01-15; Local time: 14:30:00
• Milliseconds supported: 14:30:00.123

Common Pitfalls

• No null type—omit key entirely for optional values
• Arrays must be homogeneous (TOML 1.0)—TOML 1.1 allows mixed types
• Trailing commas not allowed in arrays or inline tables
• Comment # only outside strings—no inline comment after value on same line works, but avoid ambiguity