TOML Parser for Node.js

If you haven't heard of TOML, well you're just missing out. Go check it out now. Back? Good.

TOML Spec Support

toml-node supports TOML v1.1.0, scoring 702/708 (99.2%) on the official toml-test compliance suite:

| | Pass | Total | Rate | |---|---|---|---| | Valid tests | 218 | 218 | 100% | | Invalid tests | 484 | 490 | 98.8% | | Total | 702 | 708 | 99.2% |

The 6 remaining failures are inherent JavaScript platform limitations shared by all JS TOML parsers: they cover UTF-8 encoding validation, which Node.js handles at the engine level before the parser sees the data.

Note that integers beyond Number.MAX_SAFE_INTEGER require the bigint option to parse losslessly; without it they throw a parse error rather than silently losing precision.

Feature Support

• Strings: basic, literal, multiline, all escape sequences (\uXXXX, \UXXXXXXXX, \xHH, \e)
• Integers: decimal, hexadecimal (0xDEADBEEF), octal (0o755), binary (0b11010110)
• Floats: decimal, scientific notation, inf, -inf, nan
• Booleans: true, false
• Dates/Times: offset date-time, local date-time, local date, local time; seconds optional
• Arrays: mixed types allowed
• Tables: standard, inline (with dotted/quoted keys, newlines, trailing commas), array of tables
• Keys: bare, quoted, dotted (fruit.apple.color = "red")
• Comments: # line comments

Installation

npm install toml

Requires Node.js 20 or later. Zero runtime dependencies.

Usage

const toml = require('toml');
const data = toml.parse(someTomlString);

toml.parse throws an exception on parse errors with line and column properties:

try {
  toml.parse(someBadToml);
} catch (e) {
  console.error(`Parsing error on line ${e.line}, column ${e.column}: ${e.message}`);
}

Nesting Depth Limit

To guard against stack overflow on maliciously deep input, arrays and inline tables may nest at most 500 levels deep by default; input past the limit throws a normal parse error. Adjust the limit with the maxDepth option:

toml.parse(someTomlString, { maxDepth: 100 });

Integer Range and BigInt

TOML requires parsers to handle the full range of 64-bit signed integers, but JavaScript's number type can only represent integers up to Number.MAX_SAFE_INTEGER (2⁵³ − 1) losslessly. By default, toml.parse returns integers as number and throws a parse error when a value falls outside the safe range, rather than silently returning a rounded value:

toml.parse('id = 771752188537605140');
// Error: Integer 771752188537605140 cannot be represented losslessly
// as a JavaScript number. Use the `bigint` option to parse integers
// as BigInt values.

Pass bigint: true to instead parse all integers as BigInt, preserving the full 64-bit range:

const data = toml.parse('id = 771752188537605140\ncount = 3', { bigint: true });
data.id     // 771752188537605140n
data.count  // 3n

Integers outside the 64-bit signed range always throw, in either mode, as required by the spec. Floats are unaffected by all of this: TOML floats are IEEE 754 binary64 values, which is exactly what a JavaScript number is, so every TOML float is represented as faithfully as the spec intends.

Date/Time Values

Offset date-times are returned as JavaScript Date objects. Local date-times, local dates, and local times are returned as strings since they have no timezone information and can't be losslessly represented as Date:

const data = toml.parse(`
odt = 1979-05-27T07:32:00Z       # Date object
ldt = 1979-05-27T07:32:00        # string: "1979-05-27T07:32:00"
ld  = 1979-05-27                  # string: "1979-05-27"
lt  = 07:32:00                    # string: "07:32:00"
`);

data.odt instanceof Date  // true
typeof data.ldt            // "string"
typeof data.ld             // "string"
typeof data.lt             // "string"

Temporal Support

Pass useTemporal: true to have date/time values returned as Temporal objects instead:

| TOML type | Returned as | | ---------------- | ------------------------- | | Offset date-time | Temporal.ZonedDateTime | | Local date-time | Temporal.PlainDateTime | | Local date | Temporal.PlainDate | | Local time | Temporal.PlainTime |

const data = toml.parse(`
odt = 1979-05-27T00:32:00-07:00
ldt = 1979-05-27T07:32:00
ld  = 1979-05-27
lt  = 07:32:00
`, { useTemporal: true });

data.odt.toString()  // "1979-05-27T00:32:00-07:00[-07:00]"
data.ldt.toString()  // "1979-05-27T07:32:00"
data.ld.toString()   // "1979-05-27"
data.lt.toString()   // "07:32:00"

Offset date-times become Temporal.ZonedDateTime values whose time zone is the original UTC offset (Z maps to the UTC time zone), so the offset written in the TOML document is preserved — unlike the default Date representation, which loses it. Fractional seconds beyond nanosecond precision are truncated, as permitted by the TOML spec.

useTemporal requires a runtime with the Temporal global. On runtimes that don't provide it yet, pass an implementation such as @js-temporal/polyfill via the temporal option:

const { Temporal } = require('@js-temporal/polyfill');
const data = toml.parse(someTomlString, { useTemporal: true, temporal: Temporal });

Once Temporal is broadly available, Temporal output is expected to become the default behavior in a future major version.

Special Float Values

inf and nan are returned as JavaScript Infinity and NaN:

const data = toml.parse(`
pos_inf = inf
neg_inf = -inf
not_a_number = nan
`);

data.pos_inf === Infinity   // true
data.neg_inf === -Infinity  // true
Number.isNaN(data.not_a_number) // true

Requiring .toml Files

You can use the toml-require package to require() your .toml files with Node.js.

Building & Testing

toml-node uses the Peggy parser generator (successor to PEG.js).

npm install
npm run build
npm test
npm run test:spec           # run toml-test compliance suite
npm run test:spec:failures  # show failure details

Changes to src/toml.pegjs require a rebuild with npm run build.

License

toml-node is licensed under the MIT license agreement. See the LICENSE file for more information.