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5.0.4 • Public • Published


Encode and parse data in the Concise Binary Object Representation (CBOR) data format (RFC7049).


$ npm install --save cbor

NOTE This package now requires node.js 8.3 or higher. It will work on node.js 6, in a less-tested, less-featureful way. Please start upgrading if it is possible for you.


See the full API documentation.

For a command-line interface, see cbor-cli.


var cbor = require('cbor');
var assert = require('assert');
var encoded = cbor.encode(true); // returns <Buffer f5>
cbor.decodeFirst(encoded, function(error, obj) {
  // error != null if there was an error
  // obj is the unpacked object
  assert.ok(obj === true);
// Use integers as keys?
var m = new Map();
m.set(1, 2);
encoded = cbor.encode(m); // <Buffer a1 01 02>

Allows streaming as well:

var cbor = require('cbor');
var fs = require('fs');
var d = new cbor.Decoder();
d.on('data', function(obj){
var s = fs.createReadStream('foo');
var d2 = new cbor.Decoder({input: '00', encoding: 'hex'});
d.on('data', function(obj){

There is also support for synchronous decodes:

try {
  console.log(cbor.decodeFirstSync('02')); // 2
  console.log(cbor.decodeAllSync('0202')); // [2, 2]
} catch (e) {
  // throws on invalid input

The sync encoding and decoding are exported as a leveldb encoding, as cbor.leveldb.


The synchronous routines for encoding and decoding will have problems with objects that are larger than 16kB, which the default buffer size for Node streams. There are a few ways to fix this:

  1. pass in a highWaterMark option with the value of the largest buffer size you think you will need:
cbor.encodeOne(Buffer.alloc(40000), {highWaterMark: 65535})
  1. use stream mode. Catch the data, finish, and error events. Make sure to call end() when you're done.
const enc = new cbor.Encoder()
enc.on('data', buf => /* send the data somewhere */)
enc.on('error', console.error)
enc.on('finish', () => /* tell the consumer we are finished */)
enc.end(['foo', 1, false])
  1. use encodeAsync(), which uses the approach from approach 2 to return a memory-inefficient promise for a Buffer.

Supported types

The following types are supported for encoding:

  • boolean
  • number (including -0, NaN, and ±Infinity)
  • string
  • Array, Set (encoded as Array)
  • Object (including null), Map
  • undefined
  • Buffer
  • Date,
  • RegExp
  • url.URL
  • BigInt (If your JS version supports them)
  • bignumber

Decoding supports the above types, including the following CBOR tag numbers:

Tag Generated Type
0 Date
1 Date
2 bignumber
3 bignumber
4 bignumber
5 bignumber
32 url.URL
35 RegExp

Adding new Encoders

There are several ways to add a new encoder:

encodeCBOR method

This is the easiest approach, if you can modify the class being encoded. Add an encodeCBOR method to your class, which takes a single parameter of the encoder currently being used. Your method should return true on success, else false. Your method may call encoder.push(buffer) or encoder.pushAny(any) as needed.

For example:

class Foo {
  constructor () { = 1
    this.two = 2
  encodeCBOR (encoder) {
    const tagged = new Tagged(64000, [, this.two])
    return encoder.pushAny(tagged)

You can also modify an existing type by monkey-patching an encodeCBOR function onto its prototype, but this isn't recommended.


Sometimes, you want to support an existing type without modification to that type. In this case, call addSemanticType(type, encodeFunction) on an existing Encoder instance. The encodeFunction takes an encoder and an object to encode, for example:

class Bar {
  constructor () {
    this.three = 3
const enc = new Encoder()
enc.addSemanticType(Bar, (encoder, b) => {

Adding new decoders

Most of the time, you will want to add support for decoding a new tag type. If the Decoder class encounters a tag it doesn't support, it will generate a Tagged instance that you can handle or ignore as needed. To have a specific type generated instead, pass a tags option to the Decoder's constructor, consisting of an object with tag number keys and function values. The function will be passed the decoded value associated with the tag, and should return the decoded value. For the Foo example above, this might look like:

const d = new Decoder({tags: { 64000: (val) => {
  // check val to make sure it's an Array as expected, etc.
  const foo = new Foo() = val[0]
  foo.two = val[1]
  return foo


The tests for this package use a set of test vectors from RFC 7049 appendix A by importing a machine readable version of them from For these tests to work, you will need to use the command git submodule update --init after cloning or pulling this code. See for more information.

Get a list of build steps with npm run. I use npm run dev, which rebuilds, runs tests, and refreshes a browser window with coverage metrics every time I save a .js file. If you don't want to run the fuzz tests every time, set a NO_GARBAGE environment variable:

env NO_GARBAGE=1 npm run dev

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