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This repository contains a Go command line tool which converts JSON and YAML OpenAPI descriptions to and from equivalent Protocol Buffer representations.

Protocol Buffers provide a language-neutral, platform-neutral, extensible mechanism for serializing structured data. gnostic's Protocol Buffer models for the OpenAPI Specification can be used to generate code that includes data structures with explicit fields for the elements of an OpenAPI description. This makes it possible for developers to work with OpenAPI descriptions in type-safe ways, which is particularly useful in strongly-typed languages like Go and Dart.

gnostic reads OpenAPI descriptions into these generated data structures, reports errors, resolves internal dependencies, and writes the results in a binary form that can be used in any language that is supported by the Protocol Buffer tools. A plugin interface simplifies integration with API tools written in a variety of different languages, and when necessary, Protocol Buffer OpenAPI descriptions can be reexported as JSON or YAML.

gnostic compilation code and OpenAPI Protocol Buffer models are automatically generated from an OpenAPI JSON Schema. Source code for the generator is in the generate-gnostic directory.

Related Repositories

google/gnostic-models contains a lightweight distribution of the protobuf models generated by this project. Where a low-dependency integration of just these models is needed, Go projects can import packages from gnostic-models instead of gnostic.

google/gnostic-grpc contains a gnostic plugin that can generate an annotated Protocol Buffer description of an API that, when transcode, produces an API that conforms to a specified OpenAPI document. To go from protobuf to OpenAPI, see the protoc-gen-openapi tool in this project.

google/gnostic-go-generator contains an experimental gnostic plugin that generates a Go client for an API described by a specified OpenAPI document.


Feedback and contributions are welcome! Until there is a 1.0 release, please consider this prerelease software and work in progress. To ensure stable builds, we request that dependent projects always refer to tagged releases of gnostic.


gnostic can be run in any environment that supports Go and the Protocol Buffer Compiler.

Installation and Getting Started

The following instructions are for installing gnostic using Go modules, supported by Go 1.11 and later.

  1. Get this package by downloading it with git clone.

    git clone
    cd gnostic
  2. Verify that you have a local installation of protoc. You can get protoc here.

  3. Build gnostic with make. This uses go generate to build support code including code generated by protoc and the Go protoc plugin, which is automatically downloaded from by the script. This also builds all plugins and associated tools in this repo.

  4. Verify gnostic with make test. These tests are run by gnostic's continuous integration, so you should expect them to pass for all release versions.

  5. Run gnostic. This sample invocation creates a file in the current directory named petstore.pb that contains a binary Protocol Buffer description of a sample API.

        gnostic --pb-out=. examples/v2.0/json/petstore.json
  6. You can also compile files that you specify with a URL. Here's another way to compile the previous example. This time we're creating petstore.text, which contains a textual representation of the Protocol Buffer description. This is mainly for use in testing and debugging.

        gnostic --text-out=petstore.text
  7. For a sample application, see apps/report. This reads a binary Protocol Buffer encoding created by gnostic.

    go install ./apps/report ## automatically installed by the top-level Makefile
    report petstore.pb
  8. gnostic also supports plugins. gnostic's plugin interface is modeled on protoc's plugin.proto and is described in plugins/plugin.proto. Several plugins are implemented in the plugins directory. Others, like gnostic-grpc and gnostic-go-generator, are published in their own repositories. One such plugin is gnostic-vocabulary, which produces a summary of the word usage in an APIs interfaces. You can run gnostic-vocabulary with the following:

        gnostic examples/v2.0/json/petstore.json --vocabulary_out=.

    This will produce files named vocabulary.pb and vocabulary.json in examples/v2.0/json. For the format of vocabulary.pb, see metrics/vocabulary.proto.

  9. [Optional] A large part of gnostic is automatically-generated by the generate-gnostic tool. This uses JSON schemas to generate Protocol Buffer language files that describe supported API specification formats and Go-language files of code that will read JSON or YAML API descriptions into the generated protocol buffer models. Pre-generated versions of these files are checked into the openapiv2, openapiv3, and discovery directories. You can regenerate this code with the following:

    go install ./generate-gnostic
    generate-gnostic --v2
    generate-gnostic --v3
    generate-gnostic --discovery


Copyright 2017-2020, Google LLC.


Released under the Apache 2.0 license.

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