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Protobuf to JSON-Schema compiler

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Protobuf to JSON-Schema compiler

This takes protobuf definitions and converts them into JSONSchemas, which can be used to dynamically validate JSON messages.

Useful for people who define their data using ProtoBuf, but use JSON for the "wire" format.

"Heavily influenced" by Google's protobuf-to-BigQuery-schema compiler.


Note: This tool requires Go 1.11+ to be installed.

Install this plugin using Go:

GO111MODULE=on \
go get &&
go install


Note: This plugin requires the

CLI to be installed.

protoc-gen-jsonschema is designed to run like any other proto generator. The following examples show how to use options flags to enable different generator behaviours (more examples in the Makefile too).

protoc \ # The protobuf compiler
--jsonschema_out=. \ # jsonschema out directory
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto # proto input directories and folders


| CONFIG | DESCRIPTION | |--------|-------------| |

| Require all fields in schema | |
| Allow null values in schema | |
| Enable debug logging | |
| Disallow additional properties in schema | |
| Disallow big integers as strings | |
| Use JSON field names only | |
| Prefix the output filename with package | |
| Use proto and JSON field names |


Require all fields

Because proto3 doesn't accommodate this.

protoc \
--jsonschema_out=all_fields_required:. \
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto

Allow NULL values

By default, JSONSchemas will reject NULL values unless we explicitly allow them

protoc \
--jsonschema_out=allow_null_values:. \
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto

Enable debug logging

protoc \
--jsonschema_out=debug:. \
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto

Disallow additional properties

JSONSchemas won't validate JSON containing extra parameters

protoc \
--jsonschema_out=disallow_additional_properties:. \
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto

Disallow permissive validation of big-integers as strings

(eg scientific notation)

protoc \
--jsonschema_out=disallow_bigints_as_strings:. \
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto

Prefix generated schema files with their package name (as a directory)

protoc \
--jsonschema_out=prefix_schema_files_with_package:. \
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto

Target specific messages within a proto file

# Generates MessageKind10.jsonschema and MessageKind11.jsonschema
# Use this to generate json schema from proto files with multiple messages
# Separate schema names with '+'
protoc \
--jsonschema_out=messages=[MessageKind10+MessageKind11]:. \
--proto_path=testdata/proto testdata/proto/TwelveMessages.proto

Generate fields with JSON names

protoc \
--jsonschema_out=json_fieldnames:. \
--proto_path=testdata/proto testdata/proto/ArrayOfPrimitives.proto

Sample protos (for testing)


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