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1.7.1 • Public • Published


Better TOML parsing and stringifying all in that familiar JSON interface.

Coverage Status

TOML Spec Support

The most recent version as of 2018-06-14: v0.4.0


const TOML = require('@iarna/toml')
const obj = TOML.parse(`[abc]
foo = 123
bar = [1,2,3]`)
/* obj =
{abc: {foo: 123, bar: [1,2,3]}}
const str = TOML.stringify(obj)
/* str =
foo = 123
bar = [ 1, 2, 3 ]

Visit the project github for more examples!

Why @iarna/toml

  • 100% test coverage.

  • Faster parser:

    Benchmark results showing @iarna/toml as 55x faster than toml and 5.1x faster than toml-j0.4

  • More correct parser. (Behavior carefully drawn from the spec and tested to within an inch of its life.)

  • Smallest parser bundle (if you use @iarna/toml/parse-string), 20kb.

  • No deps.

  • Detailed and easy to read error messages‼

> TOML.parse(src)
Error: Unexpected character, expecting string, number, datetime, boolean, inline array or inline table at row 6, col 5, pos 87:
5: "abc\"" = { abc=123,def="abc" }
6> foo=sdkfj

TOML.parse(str) → Object (example)

Also available with: require('@iarna/toml/parse-string')

Synchronously parse a TOML string and return an object.

TOML.stringify(obj) → String (example)

Also available with: require('@iarna/toml/stringify)

Serialize an object as TOML.


If an object TOML.stringify is serializing has a toJSON method then it will call it to transform the object before serializing it. This matches the behavior of JSON.stringify.

The one exception to this is that toJSON is not called for Date objects because JSON represents dates as strings and TOML can represent them natively.

moment objects are treated the same as native Date objects, in this respect.

TOML.stringify.value(obj) -> String

Also available with: require('@iarna/toml/stringify').value

Serialize a value as TOML would. This is a fragment and not a complete valid TOML document.

Promises and Streaming

The parser provides alternative async and streaming interfaces, for times that you're working with really absurdly big TOML files and don't want to tie-up the event loop while it parses.

TOML.parse.async(str[, opts]) → Promise(Object) (example)

Also available with: require('@iarna/toml/parse-async')

opts.blocksize is the amount text to parser per pass through the event loop. Defaults to 40kb.

Asynchronously parse a TOML string and return a promise of the resulting object. → Promise(Object) (example)

Also available with: require('@iarna/toml/parse-stream')

Given a readable stream, parse it as it feeds us data. Return a promise of the resulting object.

readable.pipe( → Transform (example)

Also available with: require('@iarna/toml/parse-stream')

Returns a transform stream in object mode. When it completes, emit the resulting object. Only one object will ever be emitted.

Lowlevel Interface (example) (example w/ parser debugging)

You construct a parser object, per TOML file you want to process:

const TOMLParser = require('@iarna/toml/lib/toml-parser.js')
const parser = new TOMLParser()

Then you call the parse method for each chunk as you read them, or in a single call:

parser.parse(`hello = 'world'`)

And finally, you call the finish method to complete parsing and retrieve the resulting object.

const data = parser.finish()

Both the parse method and finish method will throw if they find a problem with the string they were given. Error objects thrown from the parser have pos, line and col attributes. TOML.parse adds a visual summary of where in the source string there were issues using parse-pretty-error and you can too:

const prettyError = require('./parse-pretty-error.js')
const newErr = prettyError(err, sourceString)

What's Different

For the most part, this module is stricter than the toml module and about as strict as toml-j0.4. Adherence to the spec is needed if your TOML is going to be compatible between implementations. The toml module also has some extensions that are not yet standardized into a TOML release, but likely will be in the future.


  • The toml-j0.4 and toml modules both think that keys in inline tables may not be quoted. I believe they are in error and I allow quotes. The spec says this:

    Key/value pairs take the same form as key/value pairs in standard tables.

    Standard tables allow quoted keys and further, the ABNF from the standard allows them to be quoted.

    However, be aware that if you use quoted keys in inline tables you won't be able to parse your file with the toml-j0.4 or toml modules.

Improvements to make

  • In stringify:
    • Any way to produce comments. As a JSON stand-in I'm not too worried about this.
    • Stringification could use some work on its error reporting. It reports what's wrong, but not where in your data structure it was.
  • Further optimize the parser:
    • There are some debugging assertions left in the main parser, these should be moved to a subclass.
    • Make the whole debugging parser thing work as a mixin instead of as a superclass.


You can run them yourself with:

$ npm run benchmark

The results below are from my laptop using Node 10.5.0. The library versions tested were @iarna/toml@1.6.0, toml-j0.4@1.1.1, toml@2.3.3, @sgarciac/bombadil@0.0.7. The percentage after average results is the margin of error.

@iarna/​toml toml-j0.4 toml @sgarciac/​bombadil
Overall 48.50 3.58% 8.79 3.88% 0.83 1.01% crashed
Spec Example 3616 2.04% 961 3.66% 151 2.34% 604 1.80%
Spec Example: Hard Unicode 22433 1.91% 4178 1.98% 736 3.30% 893 1.24%
1000 Keys 989 2.18% 195 0.43% 10.92 2.31% 206 1.71%
Array With 1000 Tables With 1 Key 385 1.13% 133 0.77% 6.18 1.00% 113 1.65%
Array With 1000 Tables of Tables of 1 Key 200 0.37% 79.87 1.04% 3.72 1.57% 59.53 1.70%
1000 Element Inline Array 743 0.25% 444 0.26% 133 2.56% crashed
1000 Key Inline Table 736 0.50% 332 1.27% 16.32 3.35% crashed
40kb Multiline Single Quoted String 1122 3.03% 61.77 4.01% 68.24 2.59% 782 1.00%
40kb Multiline Double Quoted String 1074 3.54% 57.27 3.33% 5.42 0.65% 825 1.60%
Inline Array Nested 1000 deep 2662 0.69% 128 0.32% 15.75 2.08% 240 1.52%
Inline Tables Nested 1000 deep 1098 0.94% 197 1.82% 16.65 2.34% 221 1.84%
40kb Double Quoted String 1044 2.62% 90.21 0.24% 5.37 1.38% 812 1.03%
40kb Single Quoted String 1105 0.60% 82.79 4.56% 75.11 2.12% 825 1.34%


I write a by hand, honest-to-god, CHANGELOG for this project. It's a description of what went into a release that you the consumer of the module could care about, not a list of git commits, so please check it out!


The test suite is maintained at 100% coverage: Coverage Status

All of the official example files from the TOML spec are run through this parser. The parser's output is compared to that of toml and toml-j0.4 to ensure we're parsing this core material in the same way.

The stringifier is tested by round tripping these same files, asserting that TOML.parse(sourcefile) deepEqual TOML.parse(TOML.stringify(TOML.parse(sourcefile))

The files are from the TOML specification as of 183273af30102704a103f206f974636967c4da6d and specifically are:

Additional tests look at some more unusual use cases and error conditions are were drawn up primarily while achieving 100% coverage and are found in test/specific.js and and test/error.js respectively. Relatedly, test/stringify.js contains the same for stringification. Tests for the parsers debugging mode live in test/devel.js.

And finally, many stringification tests were borrowed from @othiym23's toml-stream module. They were fetched as of b6f1e26b572d49742d49fa6a6d11524d003441fa.


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