@mcp-apps/streamable-ui-kit

A Node host for MCP Streamable HTTP, protocol 2025-11-25. MIT licensed. Extracted from Claimbite so other projects can run the same host without the bill-auditing app.

It wraps @modelcontextprotocol/sdk 1.32.1 WebStandardStreamableHTTPServerTransport and fixes two gaps that showed up when that transport was mounted on Node http:

• A pre-read request body was forwarded into the web-standard transport, and Node then wrote raw SSE bytes where a chunk-size header belonged.

• A 202 or 204 with no Content-Length was framed as chunked, and fetch().text() never returned.

writeWebResponse drops transfer-encoding from the SDK response and sets Content-Length: 0 on 202 and 204.

Run the example

Node 22 or newer.

npm install
npm start

That listens on http://127.0.0.1:<port>/mcp and registers one tool, ping. Origins other than localhost are rejected. GET /.well-known/oauth-protected-resource returns RFC 9728 metadata with authorization_servers: [].

npm test

Related MCP server: MCP Compatible Server

Use it

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { startStreamableMcpServer } from "@mcp-apps/streamable-ui-kit";

const running = await startStreamableMcpServer({
  createServer: (client) => {
    const server = new McpServer({ name: "example", version: "0.0.1" });
    if (!client.elicitation) {
      // The client did not advertise elicitation. Refuse side effects in your tools.
    }
    return server;
  },
});

client.elicitation is true when the initialize body includes capabilities.elicitation. This package reports that flag. It does not refuse a tool call by itself.

parseSseEvents and parseSseJson live in @mcp-apps/streamable-ui-kit/sse and import nothing. A browser client can use them to read notifications/progress and a mid-stream elicitation/create before the POST body closes.

The package depends on @modelcontextprotocol/sdk and @cfworker/json-schema. It is not published to npm. Install from this repository.