Hoppscotch

Hoppscotch is an open-source API development ecosystem for building, sending, and inspecting API requests, positioned as an alternative to Postman and Insomnia. It supports the full range of HTTP methods (including custom methods some APIs use) plus GraphQL, WebSocket, Server-Sent Events, and other protocols, with real-time request/response handling in a deliberately lightweight, minimalist interface.

It's available as a web app, desktop app, and CLI, and can run fully offline, on-premises, or in the cloud depending on how a team wants to deploy it. As a Progressive Web App it supports instant loading and offline use via service workers, and its themes and settings sync across cloud or local sessions.

Hoppscotch is a fit for developers who want a fast, self-hostable API client for building and testing requests during development, rather than a proprietary desktop-only tool.