Responsively App is a modified browser designed specifically for web developers who need to test responsive designs across multiple screen sizes simultaneously. It solves the pain point of manually resizing browser windows or switching between devices during development, offering a unified environment where all device views are displayed side-by-side with synchronized interactions. Built with Electron, React, and Redux, it runs natively on Mac, Windows, and Linux and integrates with browser extensions for seamless workflow integration.
The app leverages real browser engines (Chromium-based) to render pages accurately and includes developer tools like the Unified Inspector, hot reloading, and device profile customization. It’s open source, free to use, and supports package managers like Homebrew, Chocolatey, and winget for easy installation.
What You Get
- Mirrored User-interactions across all devices - Clicks, scrolls, and navigation actions performed on one device view are instantly replicated across all other device views in real time, eliminating repetitive testing.
- Unified Inspector for all devices - A single inspector panel lets you hover over any element to view its CSS properties, dimensions, and box model across all device previews simultaneously, using Cmd/Ctrl+I to activate.
- 30+ built-in device profiles - Pre-configured screen sizes for iPhones, iPads, Android devices, desktops, and tablets, with the ability to add custom device dimensions via UI.
- One-click screenshots of all devices - Capture full-page screenshots of every device view with a single click, or take viewport-specific screenshots using device toolbar camera icons.
- Custom Preview Suits - Save and switch between custom combinations of device layouts (e.g., mobile + tablet + desktop) for rapid context switching during testing.
- Hot reloading support - Automatically refreshes the preview when code changes are detected, accelerating iterative design and debugging workflows.
Common Use Cases
- Testing mobile-first responsive layouts - A frontend developer uses Responsively to verify how a new CSS grid layout behaves across 10+ screen sizes simultaneously, catching overflow and alignment issues before deployment.
- Client demo presentations - A UI designer showcases a website’s responsiveness to clients by flipping between device views in real time, demonstrating adaptive behavior without switching tabs or devices.
- Debugging cross-device CSS issues - A web developer identifies inconsistent button spacing on iPad vs. iPhone by using the Unified Inspector to compare computed styles across devices side-by-side.
- Automating screenshot documentation - A QA engineer generates full-device screenshots for design handoff documents with one click, replacing manual screen captures and reducing errors.
Under The Hood
Architecture
- Clear separation of concerns between UI components, system-level operations, and platform-specific logic, with distinct modules for device emulation, menu creation, and app updates
- Event-driven communication via typed interfaces ensures type-safe inter-process communication between Electron renderer and main processes
- Dependency injection is implemented through prop drilling and context providers, with well-defined data transfer objects for state flow
- Design patterns like Singleton, Factory, and Observer are applied consistently, though state management remains loosely coupled to React hooks without formal state libraries
Tech Stack
- React 18 and TypeScript form the foundation of a type-safe UI layer, enhanced with Material UI and Iconify for consistent design and scalable icons
- Next.js 14 with App Router enables server components and optimized rendering pipelines
- Redux Toolkit manages application state with immutable updates and middleware support
- Webpack 5 with environment-aware configurations supports seamless Electron integration
- Vitest and Testing Library provide comprehensive test coverage with realistic user interaction simulation
- Electron powers desktop packaging, complemented by electron-settings for persistent local storage and deep OS integration
Code Quality
- Extensive end-to-end and unit test suites validate UI interactions, navigation flows, and error recovery with high fidelity
- Consistent naming conventions and test organization mirror the application’s layered architecture, improving maintainability
- Robust error handling includes user-friendly overlays and state-clearing mechanisms to preserve UI integrity during failures
- Strong type safety, modern tooling, and thorough mocking of system APIs ensure reliability across legacy and modern code paths
What Makes It Unique
- Native Electron integration enables real-time, pixel-accurate responsive testing without external browsers or proxies
- Built-in IPC system provides seamless access to system-level APIs like clipboard and file system, eliminating external dependencies
- Dynamic device profile management with auto-refreshing environment metadata offers unmatched visibility into rendering contexts during development
- Context-aware screenshot and device switching workflows are tightly coupled with live DOM inspection, creating a unified debugging experience
- Adaptive theming with native dark mode detection and device-specific icon styling delivers a cohesive, system-respecting interface