Best Open-source API Clients & Testing tools

Requestly

Local-first API client, interceptor, and mocking platform.

Bruno

Local‑first API client that stores collections as plain files

Scalar

Instant, offline‑first OpenAPI client with modern interactive docs

Hoppscotch

Lightweight API development ecosystem for testing and collaboration

Hurl

Run and test HTTP requests from a single fast CLI

Yaak

Fast, privacy-first desktop API client for modern protocols

Insomnia

Cross-platform API client for REST, GraphQL, gRPC, and more

Cartero

Native graphical HTTP client for testing APIs freely

API Dash

Beautiful cross-platform API client with multimedia response preview

Pororoca

HTTP testing tool with HTTP/2, HTTP/3, and WebSocket support

ATAC

Terminal-based API client for free, offline HTTP testing

Restfox

Offline-First HTTP & Socket Testing Client for Web & Desktop

Yaade

Self-hosted, collaborative API development environment with multi-user support

Curlie

Curlie: curl’s power with httpie’s friendly syntax

HTTPie

Human-friendly command-line HTTP client for the API era

Firecamp

Developer-first multi-protocol API platform with VSCode-inspired experience

Ezy

Desktop gRPC and gRPC-Web client for API testing

Prestige

In-browser, text-driven HTTP client for rapid API testing.