Top 23 Java OpenAPI Projects

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1. openapi-generator

   1 264 26,395 9.9 Java

   OpenAPI Generator allows generation of API client libraries (SDK generation), server stubs, documentation and configuration automatically given an OpenAPI Spec (v2, v3)

   

   Project mention: Stop Advertising in Your Commits | news.ycombinator.com | 2026-05-26

   To be fair I've never used Laravel - but I do have a memory of code generators/scaffolders inserting files that made clear they were responsible for work

   /*

   * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).

   * Do not edit the class manually.

   */

2. SaaSHub

   www.saashub.com featured

   SaaSHub - Software Alternatives and Reviews. SaaSHub helps you find the best software and product alternatives

   

3. swagger-core

   2 6 7,528 8.7 Java

   Examples and server integrations for generating the Swagger API Specification, which enables easy access to your REST API

   

4. springfox

   3 7 5,932 0.0 Java

   Automated JSON API documentation for API's built with Spring

   

5. springdoc-openapi

   4 21 3,717 9.1 Java

   Library for OpenAPI 3 with spring-boot

   

6. Light-Java

   5 0 3,673 9.4 Java

   A fast, lightweight and more productive microservices framework

   

7. microcks

   6 1 1,960 9.6 Java

   The open source, cloud native tool for API Mocking and Testing. Microcks is a Cloud Native Computing Foundation incubating project 🚀

   

8. standard-webhooks

   7 20 1,690 7.7 Java

   The Standard Webhooks specification

   

   Project mention: Ace These 5 Backend Concepts to Become a Senior Engineer | dev.to | 2026-05-12

   Standard Webhooks is still a good reference. Not every provider follows it, but it gives a good mental model for how webhooks should work.

9. cats

   8 24 1,359 9.5 Java

   CATS is a REST API Fuzzer and negative testing tool for OpenAPI endpoints. CATS automatically generates, runs and reports tests with minimum configuration and no coding effort. Tests are self-healing and do not require maintenance. (by Endava)

   

10. Swagger Plugin for JetBrains

    9 0 1,174 5.5 Java

    A plugin to help you easily edit Swagger and OpenAPI specification files inside IntelliJ IDEA

    

11. openapi-diff

    10 5 1,085 8.7 Java

    Utility for comparing two OpenAPI specifications.

    

    Project mention: OpenAPI仕様の差分を比較し、CIで破壊的変更をブロックする方法 | dev.to | 2026-06-16

12. zilla

    11 10 691 9.3 Java

    🦎 A multi-protocol edge & service proxy. Seamlessly interface web apps, IoT clients, & microservices to Apache Kafka® via declaratively defined, stateless APIs.

    

13. Membrane Service Proxy

    12 1 610 9.8 Java

    Truly open source API gateway with native OpenAPI support. Written in Java, it is easily extensible, supports legacy XML and SOAP, and is optimized for container deployments.

    

14. spring-petclinic-rest

    13 2 578 7.7 Java

    REST version of the Spring Petclinic sample application

    

15. grpc-swagger

    14 1 441 0.0 Java

    Debugging gRPC application with swagger-ui.

    

16. swagger-petstore

    15 19 325 6.9 Java

    

17. znai

    16 5 277 9.2 Java

    Build functional, maintainable, beautiful User Guides with markdown and Znai plugins. Instant pages navigation. Local search. Multiple integrations to work with Python, Java, C++, OpenAPI, etc. Transform "getting started" sections into slideshow for your workshops. Manage multiple documentations with self-deployed znai hub.

    

18. tcases

    17 1 239 6.8 Java

    A model-based test case generator

    

19. RESTest

    18 1 233 4.6 Java

    RESTest: Automated Black-Box Testing of RESTful Web APIs

    

20. proteus

    19 0 199 4.5 Java

    Proteus is a blazing fast minimalist Java web server framework built atop Undertow. (by noboomu)

    

21. juneau

    20 0 94 9.9 Java

    Apache Juneau

    

22. oauth1-signer-java

    21 1 69 7.4 Java

    Zero dependency library for generating a Mastercard API compliant OAuth signature.

    

23. openapi-generics

    22 3 23 9.3 Java

    Prevent OpenAPI Generator from redefining your Java contract. Contract-preserving client generation for Spring Boot — available on Maven Central.

    

    Project mention: OpenAPI generators break generic API responses | news.ycombinator.com | 2026-03-30

24. Hexagonal Architecture Template

    23 0 23 6.9 Java

    Java-based microservice template built with Spring Boot, following Hexagonal Architecture (Ports and Adapters). Provides a modular REST API suitable for creating scalable, maintainable, and testable services.

    

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• OpenAPI generators break generic API responses

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• How OpenAPI Undermines a Good Developer Experience

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• 🚀 Spring Boot + OpenAPI Generator: Type-Safe Generic API Clients Without Boilerplate

  1 project | dev.to | 22 Sep 2025

• Programming in D: Tutorial and Reference

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• A note from our sponsor - SaaSHub
  www.saashub.com | 17 Jun 2026

  SaaSHub helps you find the best software and product alternatives Learn more →

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