Best Open-source API Clients & Testing tools

Bruno

Local‑first API client that stores collections as plain files

Requestly

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

Insomnia

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

Scalar

Instant, offline‑first OpenAPI client with modern interactive docs

Hurl

Run and test HTTP requests from a single fast CLI

API Dash

Beautiful cross-platform API client with multimedia response preview

Hoppscotch

Lightweight API development ecosystem for testing and collaboration

Yaak

Fast, privacy-first desktop API client for modern protocols

Cartero

Native graphical HTTP client for testing APIs freely

ATAC

Terminal-based API client for free, offline HTTP testing

Curlie

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

Pororoca

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

Restfox

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

Yaade

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

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.