@developmentseed/mcp-view

The view-side bridge for MCP Apps UI views: the ui/* postMessage protocol as two small functions.

An MCP tool can ship a UI view — an HTML bundle the server exposes as a ui://<toolset>/<id> resource, which the host renders inline in the chat instead of raw JSON. The bundle runs in a sandboxed iframe and talks to its host over ui/* JSON-RPC-over-postMessage. This package wraps the official SDK so your view never has to know which host it landed in.

npm install @developmentseed/mcp-view

Use

import { onData, sendMessage } from "@developmentseed/mcp-view";

// The tool's structuredContent, delivered by the host once the tool has run.
onData((data) => render(data));

// A user turn back into the conversation, so the model calls the next tool.
button.onclick = () => sendMessage("clip this to the Severn catchment");

That's the whole surface. onData registers your handler and connects to the host; sendMessage posts a message as if the user had typed it.

Optionally identify your view during the ui/initialize handshake — call it before the first onData or sendMessage:

import { configure } from "@developmentseed/mcp-view";

configure({ name: "dataset-gallery", version: "1.2.0" });

Hosts

The same bundle works unchanged in any MCP Apps host — Claude.ai, ChatGPT, Goose, VS Code — and in the Chainlit chat agent bundled with mcp-toolsets-runtime, which implements the host end of this protocol.

Views are progressive enhancement: a tool's message and structured content still stand on their own in a plain MCP client that can't render them, so shipping a view never makes a tool unusable anywhere.

Serving the view

Building and serving the bundle is the server's job, not this package's. If you're using mcp-toolsets-runtime, declare VIEWS = {tool_name: view_id} in your toolset and ship the built bundle at <package>/views/<view_id>.html — see CONSUMING.md.

Notes

• ESM only, with TypeScript types included.
• Versioned in lockstep with the Python mcp-toolsets-runtime distribution, from the same repository.

MIT © Development Seed