AnAPI can be thought of as an instruction manual for communication between multiple software apparatuses. For example, an API may be used for database communication between web applications. By extracting the implementation and relinquishing data into objects, an API simplifies programming.

Open source API development ecosystem -https://hoppscotch.io (open-source alternative to Postman, Insomnia)

• UpdatedOct 7, 2025
• TypeScript

Opensource IDE For Exploring and Testing API's (lightweight alternative to Postman/Insomnia)

• UpdatedOct 7, 2025
• JavaScript

The open-source, cross-platform API client for GraphQL, REST, WebSockets, SSE and gRPC. With Cloud, Local and Git storage.

• UpdatedOct 7, 2025
• TypeScript

🥧 HTTPie CLI — modern, user-friendly command-line HTTP client for the API era. JSON support, colors, sessions, downloads, plugins & more.

• UpdatedDec 17, 2024
• Python

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

• UpdatedOct 7, 2025
• Java

Scalar is an open-source API platform:　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　🌐 Modern Rest API Client　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　📖 Beautiful API References　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　✨ 1st-Class OpenAPI/Swagger Support

• UpdatedOct 8, 2025
• Vue

A RWKV management and startup tool, full automation, only 8MB. And provides an interface compatible with the OpenAI API. RWKV is a large language model that is fully open source and available for commercial use.

• UpdatedAug 21, 2025
• TypeScript

A single API for all your integrations.

• UpdatedOct 8, 2025
• TypeScript

Official Notion JavaScript Client

• UpdatedSep 25, 2025
• TypeScript

Free and open-source API Client & Interceptor.

• UpdatedOct 7, 2025
• TypeScript

📚 A collection of useful resources for building RESTful HTTP+JSON APIs.

• UpdatedAug 21, 2024

🚀 HTTPie Desktop — cross-platform API testing client for humans. Painlessly test REST, GraphQL, and HTTP APIs.

• UpdatedMar 19, 2025

Insomnium is a fast local API testing tool that is privacy-focused and 100% local. For testing GraphQL, REST, WebSockets and gRPC. This is a fork of Kong/insomnia

• UpdatedApr 20, 2024
• JavaScript

The power of curl, the ease of use of httpie.

• UpdatedAug 24, 2025
• Go

PHP Curl Class makes it easy to send HTTP requests and integrate with web APIs

• UpdatedOct 6, 2025
• PHP

OpenAI API + Ruby! 🤖❤️ GPT-5 & Realtime WebRTC compatible!

• UpdatedAug 29, 2025
• Ruby

An API Client package to access the APIs for NBA.com

• UpdatedSep 30, 2025
• Python

A simple API client (postman like) in your terminal

• UpdatedSep 25, 2025
• Rust

Developer-first OpenSource API DevTool, Postman/Insomnia alternative.

• UpdatedJul 30, 2024
• TypeScript

DummyJSON.com provides different types of REST Endpoints filled with JSON data which you can use in developing the frontend with your favorite framework and library without worrying about writing a backend.

• UpdatedSep 16, 2025
• EJS