Facet MCP server

Facet

Facet is a free, open-source tool for testing responsive web design. It shows a web page on many phones, tablets, laptops and desktop monitors at once. It mirrors what you do in one device to all the others, and it checks every screen size for layout problems while you work: sideways scrolling, tiny tap targets, unreadable text and more.

Facet is an independent, open-source alternative to Responsively App. It has the same core idea, plus real device emulation and built-in audits. It shares no code with Responsively.

It comes in three forms that share one catalogue of 292 device profiles:

• Facet Web: a website. Paste a link, see it on many screens. Nothing to install.
• Facet desktop: an Electron app with full device emulation, audits and an MCP server.
• facet-check: a command-line tool and MCP server, so CI and AI coding agents can check a page on many devices: npx @chandra14/facet-check localhost:3000.

Facet Web

https://chndr-prksh.github.io/facet/

Paste any link and it opens side by side on the devices you pick. A shared link reopens the same page on the same devices, for example this one.

• 292 device profiles with search, presets, saved sets, any custom size, and drag-resizable panes.
• Side-by-side, wrapped and one-at-a-time layouts, fit-to-window zoom, rotation, device frames.
• A/B compare: a second link beside the first on every device.
• Column-grid and thumb-reach overlays.
• Works with localhost, so you can point it at a project in development.

The limit every website of this kind has. A site can tell browsers not to display it inside another page, and most large sites do (55 of 71 popular sites checked in October 2026). Facet Web detects this and says so instead of showing an unexplained blank pane. Because it uses frames, it also gets the viewport size exactly right but cannot change pixel density, touch input or the user agent; the desktop app does.

Facet Helper (in extension/) is a small Chrome and Edge extension that removes that limit. In tabs showing Facet Web, and only there, it strips the headers that forbid framing, so any site loads. It also mirrors scrolling, clicks, typing and navigation between devices and flags devices where the page overflows sideways. Install it from the Help panel on the site (download, unzip, Load unpacked). It is not on the Chrome Web Store.

npm run web:dev        # the website on http://localhost:5180
npm run test:web       # 21 checks, with and without the extension

Pushing to main deploys the site to GitHub Pages.

Command line, CI and AI agents

facet-check loads a page in headless Chromium on several emulated devices and reports the problems on each. It gives the element at fault and how to fix it.

npx @chandra14/facet-check example.com                      # the six most common screen sizes
npx @chandra14/facet-check localhost:3000 -d phones --screenshots shots
npx @chandra14/facet-check https://example.com --json --fail-on error   # for CI

It also runs as an MCP server, so a coding agent can check its own CSS changes across screen sizes:

claude mcp add facet -- npx -y @chandra14/facet-check mcp

Tools: checkresponsive, screenshot, compareelement, auditaccessibility, listdevices. See cli/README.md for every option.

Run the desktop app

npm install
npm run dev        # development, with hot reload
npm run pack       # builds dist/mac-arm64/Facet.app (unsigned)
npm test           # 55 end-to-end checks against the built app

Shortened. The full README is on GitHub.