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Workflow Server MCP Demo (browser)

A browser demo for the @eclipse-glsp/server-mcp portable Fetch handler. The page opens a workflow GLSP session inside an in-page Web Worker and drives the MCP server through a Service Worker that intercepts fetch('/mcp', …) and proxies the request to the Worker via MessageChannel.

This package is private — it ships nothing; it's a local demo and manual test bench for the portable handler.

Why only a browser demo?

The browser variant needs a custom harness because external MCP clients can't reach an in-page launcher: a browser tab doesn't accept inbound network traffic. The Service Worker in this demo is what makes the in-page launcher reachable to a same-origin MCP client.

For the Node variant, no demo is needed in this repo — the launcher binds a real HTTP listener and announces its URL via stdout ([GLSP-MCP-Server]:Ready. {…}). Point any MCP client at that URL:

  • The official MCP Inspector is the best manual debug tool — runs as a local web UI and lets you exercise tools, prompts and resources interactively.
  • Claude Code, Cursor, or any other MCP-aware client also work.

The Node path is additionally covered by the automated end-to-end spec at packages/server-mcp/src/node/server/mcp-http-transport-e2e.spec.ts, which runs an MCP SDK Client over real HTTP against the launcher.

Running

From the repository root:

yarn workspace @eclipse-glsp-examples/workflow-server build
yarn workspace @eclipse-glsp-examples/workflow-server-mcp-demo start

The start script copies the worker bundle from @eclipse-glsp-examples/workflow-server-bundled-web, builds the page-side bundle, and serves the directory on http://localhost:8000/.

Open http://localhost:8000/ in a Chromium-based browser. Step through the buttons top-to-bottom; the workflow auto-renders once MCP is initialized, and Create task mutates the live session.

What it exercises

  1. The page acts as a minimal GLSP JSON-RPC client over postMessage to the in-page Web Worker (using vscode-jsonrpc/browser, bundled).
  2. GLSP initialize carries mcpServer: {} — the Worker's per-connection child container activates BrowserMcpServerModule's launcher as a GLSPServerInitializer.
  3. initializeClientSession opens a real workflow GLSP session with diagramType: workflow-diagram.
  4. A Service Worker (mcp-service-worker.js) intercepts fetch('/mcp', …) and proxies the request through a MessageChannel to the Worker.
  5. MCP tools (initialize, tools/list, session-info, query-elements, diagram-model, create-nodes) round-trip end-to-end against the live session.

The on-page SVG is a minimal schematic renderer — not the GLSP client; its only purpose is to make the MCP handlers' output visible so the demo can be eyeballed end-to-end.

Hard reset

If a stale Service Worker is misbehaving: DevTools → Application → Service Workers → Unregister, then close the tab and re-open. The page's Worker bundle URL is cache-busted per load, but the SW itself updates only on full lifecycle restart.