proto3 JSON serializer for TypeScript / JavaScript

This library implements proto3 JSON serialization and deserialization for protobuf.js protobuf objects according to the spec.

Note that the spec requires special representation of some google.protobuf.* types (Value, Struct, Timestamp, Duration, etc.), so you cannot just use .toObject() since the result won't be understood by protobuf in other languages. Hence this module.


const serializer = require('proto3-json-serializer');


import * as serializer from 'proto3-json-serializer';

Serialization: protobuf.js object to proto3 JSON

const root = protobuf.loadSync('test.proto');
const Type = root.lookupType('test.Message');
const message = Type.fromObject({...});

const serialized = serializer.toProto3JSON(message);

Serialization works with any object created by calling .create(), .decode(), or .fromObject() for a loaded protobuf type. It relies on the $type field so it will not work with a static object.

Deserialization: proto3 JSON to protobuf.js object

To deserialize an object from proto3 JSON, we must know its type (as returned by root.lookupType('...')). Pass this type as the first parameter to .fromProto3JSON:

const root = protobuf.loadSync('test.proto');
const Type = root.lookupType('test.Message');
const json = {...};

const deserialized = serializer.fromProto3JSON(Type, json);

Complete example

const assert = require('assert');
const path = require('path');
const protobuf = require('protobufjs');
const serializer = require('proto3-json-serializer');

// We'll take sample protos from google-proto-files but the code will work with any protos
const protos = require('google-proto-files');

// Load some proto file
const rpcProtos = protos.getProtoPath('rpc');
const root = protobuf.loadSync([
    path.join(rpcProtos, 'status.proto'),
    path.join(rpcProtos, 'error_details.proto'),
const Status = root.lookupType('google.rpc.Status');

// If you have a protobuf object that follows proto3 JSON syntax
// (this is an example of google.rpc.Status message in JSON)
const json = {
    code: 3,
    message: 'Test error message',
    details: [
            '@type': 'google.rpc.BadRequest',
            fieldViolations: [
                    field: 'field',
                    description: 'must not be null',

// You can deserialize it into a protobuf.js object:
const deserialized = serializer.fromProto3JSON(Status, json);

// And serialize it back
const serialized = serializer.toProto3JSON(deserialized);
assert.deepStrictEqual(serialized, json);


This is not an officially supported Google project.