Bruno is a comprehensive API client and testing tool built with Electron, React, and Redux. It provides a full-featured interface for creating, sending, and analyzing HTTP/WebSocket/gRPC/GraphQL requests, similar to Postman but with an open-source core. The application features a modular architecture with separate packages for the GUI (bruno-app), Electron main process (bruno-electron), CLI (bruno-cli), request handling (bruno-requests), file storage (bruno-filestore), and shared utilities (bruno-common). Key capabilities include environment and variable management with secure secret handling, pre-request and test scripting using a custom BruJS runtime, collection organization and workspaces, import/export from formats like Postman, OpenAPI, and Insomnia, mock server functionality, and code generation from requests. The UI uses styled-components for theming with light/dark/system themes, and incorporates advanced features like AI-assisted request building and OpenAPI synchronization. The codebase demonstrates strong engineering practices with extensive unit and end-to-end testing, TypeScript throughout, and a clean separation of concerns between the main and renderer processes via IPC. Notable reusable components include a secure variable interpolation system, cross-platform detection utilities, persistent state hooks, and a worker-offloaded file format parser.