Responsively App is a free, open-source modified web browser built on Electron that previews a page at several device sizes at once and mirrors interactions across them, aimed at web developers doing responsive front-end work.

What it is

It is a desktop application written in TypeScript and released under the AGPL-3.0 licence, distributed through responsively.app and the responsively-org GitHub organisation, where it has roughly 25,200 stars, 1,403 forks and 324 open issues, with activity as recent as September 2026. Instead of a single viewport it presents a customizable layout of device previews of the same page and mirrors clicks, keystrokes and navigation across all of them.

The problem it solves is the slow loop of responsive testing: in a standard browser a developer checks one viewport at a time, resizing the window or opening device emulation, inspecting what changed, and then repeating the process at the next breakpoint. Responsively App replaces that one-device-at-a-time preview workflow with a single workspace holding 30+ built-in device profiles, one shared elements inspector and one-click screenshots. It also ships a browser extension for sending links from Chrome, Firefox or Edge straight into the app, and a built-in Model Context Protocol server that lets AI coding agents drive the same previews.

Key capabilities

• Mirrored user interactions across all device previews, so a click, a typed key or a navigation is applied to every device at once.
• A customizable preview layout for arranging the devices under test.
• One elements inspector shared by every device in the preview.
• 30+ built-in device profiles, with the option to add custom devices.
• One-click screenshots across all devices in the preview.
• Hot reloading support, so a running dev server refreshes in the previews as code is saved.
• A Model Context Protocol server on http://127.0.0.1:12720/mcp exposing tools such as navigate, list_devices, set_active_devices, screenshot, read_page, click and type_text; screenshots are JPEG images downscaled to at most 1000px wide.

Who uses it and how

• Front-end and responsive web developers who want phone, tablet and desktop widths visible at the same time rather than one after another.
• Developers running a local dev server with hot reloading, who keep the app open beside the editor and watch every preview update on save.
• Teams using AI coding agents: Claude Code connects with claude mcp add responsively -- npx -y @responsively/mcp and Cursor through a .cursor/mcp.json entry, after which the agent can load a URL, change active devices, click and type, and capture per-device screenshots for visual verification; the app starts on demand at the first tool call and is reused if it is already running.
• Developers on macOS, Windows or Linux who need a batch of screenshots across every configured device in one click.

Getting started

The application is downloaded from responsively.app for macOS, Windows and Linux, or installed with brew install --cask responsively, choco install responsively, winget install ResponsivelyApp, an rpm package, or a Linux AppImage from the releases page. The agent integration is added with claude mcp add responsively -- npx -y @responsively/mcp, or by pointing a client at http://127.0.0.1:12720/mcp while the app is running.

How it compares

No list of paid products that Responsively App replaces is given in the facts, and no comparable tool is named alongside it, so it stands alone in this registry with nothing here to measure it against directly. The only positioning the facts support is the project's own: a free, open-source application under AGPL-3.0 whose topics describe it as an opensource-alternative.

When to use it — and when not to

Because it is a desktop application rather than a hosted service, there is no database or SMTP to operate, but every developer has to install and run it locally, and the MCP server only listens on localhost while the app is open. Teams that need a browser-based or headless tool, or that cannot install desktop software on developer machines, should look elsewhere, and anyone redistributing a modified build should read the AGPL-3.0 obligations first. The README excerpt is thin and partly truncated, and 324 open issues indicate a sizeable backlog.

brew install --cask responsively

choco install responsively

winget install ResponsivelyApp

sudo rpm -i https://github.com/responsively-org/responsively-app/releases/download/v[VERSION]/Responsively-App-[VERSION].x86_64.rpm

claude mcp add responsively -- npx -y @responsively/mcp

{
  "mcpServers": {
    "responsively": {"command": "npx", "args": ["-y", "@responsively/mcp"]}
  }
}

claude mcp add --transport http responsively http://127.0.0.1:12720/mcp