pi-mcp-apps0.1.0

Render MCP Apps (SEP-1865) from the servers already connected in pi

richardanaya Published 8 days ago MIT ~279 downloads/mo

Untested on omp

This is a pi package. No one has reported whether it works on omp yet. If you try it, add your result below.

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pi-mcp-apps

Pi extension for MCP Apps, stable 2026-01-26, extension id io.modelcontextprotocol/ui.

It uses the MCP servers already connected in Pi. It does not open a second connection and it does not register a slash command.

What the host does

During MCP initialize, the client advertises:

{ "io.modelcontextprotocol/ui": { "mimeTypes": ["text/html;profile=mcp-app"] } }

When Pi reports hasUI and a tool result comes from a tool whose _meta.ui.resourceUri is a ui:// resource, the extension reads that resource and hosts the page. It does not launch a browser. The deprecated flat _meta["ui/resourceUri"] key is still accepted. mcp_apps_open hosts a URI you name. HTML may arrive as text or base64 blob. The MIME type must be text/html;profile=mcp-app.

The words "Open MCP App" are drawn under the tool call as a clickable link only when Pi reports hasUI. Console and print mode leave the tool result unchanged and do not host a page for it. mcp_apps_open still returns a URL when called.

Tools with visibility that does not include "model" are removed from the active tool list. "app" is required before this host will proxy tools/call from a view, and the call stays on that view's server. Omitted visibility means ["model", "app"].

Page and sandbox

Open the link in a browser. The page is 127.0.0.1. The app runs in a sandboxed iframe on 127.0.0.2 at the same port. The outer sandbox iframe is allow-scripts allow-same-origin. The inner view iframe is allow-scripts.

The sandbox sends ui/notifications/sandbox-proxy-ready. The host answers with ui/notifications/sandbox-resource-ready, including the raw HTML, the CSP, and any permission policy from _meta.ui. The sandbox injects that CSP and sets the inner allow attribute. Undeclared origins are dropped. If the resource omits CSP, the header is the spec default: default-src 'none', 'self' plus 'unsafe-inline' for scripts and styles, img-src and media-src limited to 'self' and data:, connect-src 'none', frame-src 'none', object-src 'none', base-uri 'self'.

After ui/notifications/initialized, the host sends ui/notifications/tool-input, ui/notifications/tool-result, and ui/notifications/host-context-changed with the window size. Nothing is sent to the view before initialized.

ui/initialize returns protocol 2026-01-26, host info, openLinks, serverTools, serverResources, logging, the sandbox CSP that was applied, and host context (inline only, desktop, locale, time zone). ui/request-display-mode always results in inline. This host does not offer fullscreen or picture-in-picture.

View requests

Method	Behavior
`ping`	Empty result
`tools/call`	Proxied when visibility includes `app`
`resources/read`	Proxied to the same server
`notifications/message`	Accepted
`ui/message`	`role: "user"` text is delivered with `sendUserMessage` (`deliverAs: "followUp"`)
`ui/update-model-context`	Stored and added on later turns. It does not start a turn
`ui/open-link`	`http:` and `https:` URLs are opened with `xdg-open`
`ui/request-display-mode`	Stays `inline`

tools/call from the view returns the server result to the view. It does not start a model turn.

Install

Node 22 or newer. Peer dependency @earendil-works/pi-coding-agent 1.0.1. The hook also patches the running Pi 1.1 bundle at dist/bundle/chunks/runtime-*.js.

pi install npm:pi-mcp-apps

Local load: pi -e ~/repos/pi-mcp-apps/index.ts.

Not in this host

Partial tool-argument streaming, theme CSS variables, and ui/resource-teardown are not sent. Views live until the Pi process exits. A dedicated domain from resource metadata is not mapped to another origin; the sandbox origin is always 127.0.0.2.