Kaleidoscope

Kaleidoscope is a responsive preview and inspection tool for web apps. Load a local or public URL once, view it across device profiles, capture screenshots, inspect trusted local pages, and let MCP clients automate the workflow.

What You Can Do

• Preview local and public HTTP/HTTPS pages across mobile, tablet, and desktop devices.

• Compare multiple breakpoints side by side.

• Capture screenshots across several device profiles in one run.

• Record scripted walkthrough videos with visible cursor movement.

• Preview authenticated pages with temporary cookie and header injection.

• Inspect trusted local pages and map selected elements back to source context.

• Use MCP tools from Claude Code, Codex, Cursor, Windsurf, VS Code, and other stdio MCP clients.

Visual Tour

Install

Install the MCP package globally:

npm install -g kaleidoscope-mcp-server

The executable name is:

kaleidoscope-mcp

Screenshots and walkthrough recording require Playwright Chromium:

npx playwright install chromium

The npm package includes the Kaleidoscope MCP server, backend, and built web client. When an MCP tool needs Kaleidoscope and no server is already running, it can start the packaged runtime automatically.

MCP Client Setup

Use kaleidoscope-mcp as a stdio MCP server command.

Claude Code, Claude Desktop, Cursor, Windsurf, VS Code, and similar clients:

{
  "mcpServers": {
    "kaleidoscope": {
      "command": "kaleidoscope-mcp",
      "env": {
        "KALEIDOSCOPE_SERVER_URL": "http://localhost:5000"
      }
    }
  }
}

Codex config.toml:

[mcp_servers.kaleidoscope]
command = "kaleidoscope-mcp"
enabled = true
startup_timeout_sec = 20
tool_timeout_sec = 60

[mcp_servers.kaleidoscope.env]
KALEIDOSCOPE_SERVER_URL = "http://localhost:5000"

Codex desktop connector UI:

• Name: kaleidoscope

• Transport: STDIO

• Command to launch: kaleidoscope-mcp

• Arguments: leave empty

• Environment variable: KALEIDOSCOPE_SERVER_URL=http://localhost:5000

• Working directory: leave blank

You can also run it ad hoc with npx:

npx -y kaleidoscope-mcp-server

For MCP clients that use JSON config:

{
  "mcpServers": {
    "kaleidoscope": {
      "command": "npx",
      "args": ["-y", "kaleidoscope-mcp-server"],
      "env": {
        "KALEIDOSCOPE_SERVER_URL": "http://localhost:5000"
      }
    }
  }
}

On Windows, using the installed kaleidoscope-mcp command is usually more reliable than wrapping npx through cmd /c.

Common Workflows

Preview A Local App

1. Start your app, for example on http://localhost:3000.

2. Ask your MCP client to run kaleidoscope_start.

3. Ask it to prepare a responsive preview for your URL.

4. Open http://localhost:5000 if you want to use the visual workspace directly.

Capture Screenshots

Use capture_screenshots with device IDs or common names:

{
  "url": "http://localhost:3000",
  "devices": ["iphone-14", "ipad", "desktop-hd"]
}

Responses include screenshot metadata and Markdown-ready image references when the MCP client supports rich content.

Record A Walkthrough

Use record_walkthrough with structured steps or a simple script:

click #open-settings
type "hello@example.com" into #email
click button[type="submit"]
wait 800ms

Walkthroughs are saved as local .webm files and returned as MCP artifacts.

Preview Authenticated Pages

Use preview_with_auth to create a temporary proxy session with cookies or safe custom headers. This is useful for checking logged-in screens without changing your app.

Inspect A Local Page

Inspect mode works with trusted loopback targets such as localhost and 127.0.0.1. It can discover likely selectors and return source context for selected elements when a workspace root is configured.

MCP Tools

• kaleidoscope_status, kaleidoscope_start, kaleidoscope_stop

• kaleidoscope_list_devices

• preview_responsive

• capture_screenshots

• record_walkthrough

• preview_with_auth

• inject_mock_data

• discover_page_elements

• inspect_element_source

Environment Options

• KALEIDOSCOPE_SERVER_URL: Kaleidoscope backend URL. Defaults to http://localhost:5000.

• KALEIDOSCOPE_REQUEST_TIMEOUT_MS: MCP request timeout. Defaults to 60000.

• KALEIDOSCOPE_WORKSPACE_ROOT: source-inspection root for local projects.

• KALEIDOSCOPE_ARTIFACT_ROOT: allowed root for user-selected walkthrough output directories.

• KALEIDOSCOPE_WALKTHROUGH_DIR: default output directory for walkthrough videos.

• KALEIDOSCOPE_PROXY_TIMEOUT_MS: proxy request timeout. Defaults to 30000.

• KALEIDOSCOPE_PROXY_MAX_RESPONSE_BYTES: proxy response byte limit. Defaults to 10485760.

Troubleshooting

• Browser executable not found: run npx playwright install chromium in the same environment that launches the MCP server.

• spawn C:\Windows\system32\cmd.exe ENOENT: install the package globally and configure your MCP client to run kaleidoscope-mcp directly.

• sourceDir must be inside...: set KALEIDOSCOPE_WORKSPACE_ROOT to the project root you want Kaleidoscope to inspect.

• output_dir must stay inside...: set KALEIDOSCOPE_ARTIFACT_ROOT or KALEIDOSCOPE_WALKTHROUGH_DIR, then use an output directory below it.

• Port conflicts: set KALEIDOSCOPE_SERVER_URL=http://localhost:<free-port> or stop the process using port 5000.

Privacy And Safety

• Kaleidoscope is designed for local preview and inspection workflows.

• The local API binds to 127.0.0.1 by default.

• Inspect mode is limited to loopback targets, and source reads must stay under KALEIDOSCOPE_WORKSPACE_ROOT.

• Walkthrough output directories must stay under KALEIDOSCOPE_ARTIFACT_ROOT or KALEIDOSCOPE_WALKTHROUGH_DIR.

• Auth proxy sessions are temporary and cleaned up automatically.

• Public tunnel URLs created with tools such as cloudflared or ngrok should be treated as public.

License

Kaleidoscope is released under the MIT License. See LICENSE.