# msgpack-lite > Fast Pure JavaScript MessagePack Encoder and Decoder Latest version **0.2.2** (published 2026-09-02) · MIT license · 0 weekly downloads ## Install ```sh npm install msgpack-lite pnpm add msgpack-lite yarn add msgpack-lite bun add msgpack-lite ``` Provides the command `msgpack`. ## Health **Score 68/100 (B)** — status: active. Positive: has types package; no vulnerabilities; has provenance; recently updated; high maintenance score; high quality score. Warnings: low downloads; no esm support; pre 1.0. ## Facts | | | |---|---| | Version | 0.2.2 | | Published | 2026-09-02 | | First published | 2015-07-27 | | Weekly downloads | 0 | | License | MIT | | TypeScript types | separate (@types/msgpack-lite) | | Module format | CommonJS | | Dependencies | 4 | | Unpacked size | 117.4 KB | | Known vulnerabilities | 0 | | Install scripts | no | | Provenance | attested (GitHub Actions) | | GitHub stars | 1036 | | Author | @kawanet | | Maintainers | kawanet | | Keywords | arraybuffer, buffer, fluentd, messagepack, msgpack, serialize, stream, typedarray, uint8array | ## Links - npm: https://www.npmjs.com/package/msgpack-lite - Repository: https://github.com/kawanet/msgpack-lite - Issues: https://github.com/kawanet/msgpack-lite/issues - npm.io page: https://npm.io/package/msgpack-lite ## Dependencies (4) - [ieee754](https://npm.io/package/ieee754.md) ^1.2.1 - [isarray](https://npm.io/package/isarray.md) ^2.0.5 - [event-lite](https://npm.io/package/event-lite.md) ^1.0.0 - [int64-buffer](https://npm.io/package/int64-buffer.md) ^1.1.1 ## Alternatives - [flatbuffers](https://npm.io/package/flatbuffers.md) — 6.0M weekly downloads - [jwt-simple](https://npm.io/package/jwt-simple.md) — 259.5K weekly downloads - [@exodus/patch-broken-hermes-typed-arrays](https://npm.io/package/@exodus/patch-broken-hermes-typed-arrays.md) — 28.5K weekly downloads - [@native-to-anchor/buffer-layout](https://npm.io/package/@native-to-anchor/buffer-layout.md) — 12.2K weekly downloads - [binary-parser-encoder](https://npm.io/package/binary-parser-encoder.md) — 5.3K weekly downloads ## Recent versions - 0.2.2 (latest) — 2026-09-02 - 0.2.1 — 2026-08-27 - 0.2.0 — 2026-08-26 - 0.1.27 — 2026-08-26 - 0.1.26 — 2016-10-14 - 0.1.20 — 2016-04-22 - 0.1.19 — 2016-04-20 - 0.1.18 — 2016-04-13 - 0.1.17 — 2016-02-26 - 0.1.16 — 2016-02-16 - 0.1.15 — 2016-01-04 - 0.1.14 — 2015-12-21 - 0.1.13 — 2015-09-04 - 0.1.11 — 2015-08-23 - 0.1.9 — 2015-08-22 - … 4 more at https://npm.io/package/msgpack-lite/versions ## README # msgpack-lite [![Node.js CI](https://github.com/kawanet/msgpack-lite/workflows/Node.js%20CI/badge.svg?branch=main)](https://github.com/kawanet/msgpack-lite/actions/) [![npm version](https://img.shields.io/npm/v/msgpack-lite)](https://www.npmjs.com/package/msgpack-lite) [![gzip size](https://img.badgesize.io/https://cdn.jsdelivr.net/npm/msgpack-lite/dist/msgpack.min.js?compression=gzip)](https://cdn.jsdelivr.net/npm/msgpack-lite/dist/msgpack.min.js) Fast Pure JavaScript MessagePack Encoder and Decoder Online demo: [http://kawanet.github.io/msgpack-lite/](http://kawanet.github.io/msgpack-lite/) ### Encoding and Decoding MessagePack ```js const msgpack = require("msgpack-lite"); // encode from JS Object to MessagePack (Buffer) const buffer = msgpack.encode({"foo": "bar"}); // decode from MessagePack (Buffer) to JS Object const data = msgpack.decode(buffer); // => {"foo": "bar"} // if encode/decode receives an invalid argument an error is thrown ``` ### Writing to MessagePack Stream ```js const fs = require("fs"); const msgpack = require("msgpack-lite"); const writeStream = fs.createWriteStream("test.msp"); const encodeStream = msgpack.createEncodeStream(); encodeStream.pipe(writeStream); // send multiple objects to stream encodeStream.write({foo: "bar"}); encodeStream.write({baz: "qux"}); // call this once you're done writing to the stream. encodeStream.end(); ``` ### Reading from MessagePack Stream ```js const fs = require("fs"); const msgpack = require("msgpack-lite"); const readStream = fs.createReadStream("test.msp"); const decodeStream = msgpack.createDecodeStream(); // show multiple objects decoded from stream readStream.pipe(decodeStream).on("data", console.warn); ``` ### Decoding MessagePack Bytes Array ```js const msgpack = require("msgpack-lite"); // decode() accepts Buffer instance per default msgpack.decode(Buffer.from([0x81, 0xA3, 0x66, 0x6F, 0x6F, 0xA3, 0x62, 0x61, 0x72])); // decode() also accepts Array instance msgpack.decode([0x81, 0xA3, 0x66, 0x6F, 0x6F, 0xA3, 0x62, 0x61, 0x72]); // decode() accepts raw Uint8Array instance as well msgpack.decode(new Uint8Array([0x81, 0xA3, 0x66, 0x6F, 0x6F, 0xA3, 0x62, 0x61, 0x72])); ``` ### Command Line Interface A CLI tool bin/msgpack converts data stream from JSON to MessagePack and vice versa. ```sh $ echo '{"foo": "bar"}' | ./bin/msgpack -Jm | od -tx1 0000000 81 a3 66 6f 6f a3 62 61 72 $ echo '{"foo": "bar"}' | ./bin/msgpack -Jm | ./bin/msgpack -Mj {"foo":"bar"} ``` ### Installation ```sh $ npm install --save msgpack-lite ``` ### Tests Run tests on node.js: ```sh $ make test ``` ### Browser Build Browser version [msgpack.min.js](https://cdn.jsdelivr.net/npm/msgpack-lite/dist/msgpack.min.js) is also available. 50KB minified, 14KB gziped. ```html ``` ### MessagePack Mapping Table The following table shows how JavaScript objects (value) will be mapped to [MessagePack formats](https://github.com/msgpack/msgpack/blob/master/spec.md) and vice versa. Source Value|MessagePack Format|Value Decoded ----|----|---- null, undefined|nil format family|null Boolean (true, false)|bool format family|Boolean (true, false) Number (32bit int)|int format family|Number (int or double) Number (64bit double)|float format family|Number (double) String|str format family|String Buffer|bin format family|Buffer Array|array format family|Array Map|map format family|Map (if `usemap=true`) Object (plain object)|map format family|Object (or Map if `usemap=true`) Object (see below)|ext format family|Object (see below) Note that both `null` and `undefined` are mapped to nil `0xC1` type. This means `undefined` value will be *upgraded* to `null` in other words. ### Extension Types The MessagePack specification allows 128 application-specific extension types. The library uses the following types to make round-trip conversion possible for JavaScript native objects. Type|Object|Type|Object ----|----|----|---- 0x00||0x10| 0x01|EvalError|0x11|Int8Array 0x02|RangeError|0x12|Uint8Array 0x03|ReferenceError|0x13|Int16Array 0x04|SyntaxError|0x14|Uint16Array 0x05|TypeError|0x15|Int32Array 0x06|URIError|0x16|Uint32Array 0x07||0x17|Float32Array 0x08||0x18|Float64Array 0x09||0x19|Uint8ClampedArray 0x0A|RegExp|0x1A|ArrayBuffer 0x0B|Boolean|0x1B|Buffer 0x0C|String|0x1C| 0x0D|Date|0x1D|DataView 0x0E|Error|0x1E| 0x0F|Number|0x1F| Other extension types are mapped to built-in ExtBuffer object. ### Custom Extension Types (Codecs) Register a custom extension type number to serialize/deserialize your own class instances. ```js const msgpack = require("msgpack-lite"); const codec = msgpack.createCodec(); codec.addExtPacker(0x3F, MyVector, myVectorPacker); codec.addExtUnpacker(0x3F, myVectorUnpacker); const data = new MyVector(1, 2); const encoded = msgpack.encode(data, {codec: codec}); const decoded = msgpack.decode(encoded, {codec: codec}); function MyVector(x, y) { this.x = x; this.y = y; } function myVectorPacker(vector) { const array = [vector.x, vector.y]; return msgpack.encode(array); // return Buffer serialized } function myVectorUnpacker(buffer) { const array = msgpack.decode(buffer); return new MyVector(array[0], array[1]); // return Object deserialized } ``` The first argument of `addExtPacker` and `addExtUnpacker` should be an integer within the range of 0 and 127 (0x0 and 0x7F). `myVectorPacker` is a function that accepts an instance of `MyVector`, and should return a buffer representing that instance. `myVectorUnpacker` is the opposite: it accepts a buffer and should return an instance of `MyVector`. If you pass an array of functions to `addExtPacker` or `addExtUnpacker`, the value to be encoded/decoded will pass through each one in order. This allows you to do things like this: ```js codec.addExtPacker(0x00, Date, [Number, msgpack.encode]); ``` You can also pass the `codec` option to `msgpack.Decoder(options)`, `msgpack.Encoder(options)`, `msgpack.createEncodeStream(options)`, and `msgpack.createDecodeStream(options)`. If you wish to modify the default built-in codec, you can access it at `msgpack.codec.preset`. ### Custom Codec Options `msgpack.createCodec()` function accepts some options. It does NOT have the preset extension types defined when no options given. ```js const codec = msgpack.createCodec(); ``` `preset`: It has the preset extension types described above. ```js const codec = msgpack.createCodec({preset: true}); ``` `safe`: It runs a validation of the value before writing it into buffer. This is the default behavior for some old browsers which do not support `ArrayBuffer` object. ```js const codec = msgpack.createCodec({safe: true}); ``` `useraw`: It uses `raw` formats instead of `bin` and `str`. ```js const codec = msgpack.createCodec({useraw: true}); ``` `int64`: It decodes msgpack's `int64`/`uint64` formats with [int64-buffer](https://github.com/kawanet/int64-buffer) object. ```js const codec = msgpack.createCodec({int64: true}); ``` `binarraybuffer`: It ties msgpack's `bin` format with `ArrayBuffer` object, instead of `Buffer` object. ```js const codec = msgpack.createCodec({binarraybuffer: true, preset: true}); ``` `uint8array`: It returns Uint8Array object when encoding, instead of `Buffer` object. ```js const codec = msgpack.createCodec({uint8array: true}); ``` `usemap`: Uses the global JavaScript Map type, if available, to unpack MessagePack map elements. ```js const codec = msgpack.createCodec({usemap: true}); ``` ### Compatibility Mode The [compatibility mode](https://github.com/kawanet/msgpack-lite/issues/22) respects for [msgpack's old spec](https://github.com/msgpack/msgpack/blob/master/spec-old.md). Set `true` to `useraw`. ```js // default mode handles both str and bin formats individually msgpack.encode("Aa"); // => (str format) msgpack.encode(Buffer.from([0x41, 0x61])); // => (bin format) msgpack.decode(Buffer.from([0xa2, 0x41, 0x61])); // => 'Aa' (String) msgpack.decode(Buffer.from([0xc4, 0x02, 0x41, 0x61])); // => (Buffer) // compatibility mode handles only raw format both for String and Buffer const options = {codec: msgpack.createCodec({useraw: true})}; msgpack.encode("Aa", options); // => (raw format) msgpack.encode(Buffer.from([0x41, 0x61]), options); // => (raw format) msgpack.decode(Buffer.from([0xa2, 0x41, 0x61]), options); // => (Buffer) msgpack.decode(Buffer.from([0xa2, 0x41, 0x61]), options).toString(); // => 'Aa' (String) ``` ### Repository - [https://github.com/kawanet/msgpack-lite](https://github.com/kawanet/msgpack-lite) ### See Also - [http://msgpack.org/](http://msgpack.org/) ### License The MIT License (MIT) Copyright (c) 2015-2026 Yusuke Kawasaki Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. --- _Source: https://npm.io/package/msgpack-lite · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._