WebWeaver Nexus MCP Server

An MCP server that exposes WebWeaver Nexus services — waitlist signup (with an embedded form UI), product overview, and contact info — to MCP-enabled hosts (Claude Desktop, claude.ai, ChatGPT, Cursor, MCP Inspector, basic-host).

Production URL: https://webweaver-nexus-mcp.vercel.app/mcp — Streamable HTTP, public, no authentication.

Published to the official MCP registry as io.github.webweaver-nexus/webweaver-mcp-server (v1.0.0).

Tools

Related MCP server: nexusm-mcp-server

Prerequisites

• Node.js 20+

• npm

Install

npm install

Build

npm run build

This runs TypeScript type-checking, bundles the MCP App UI with Vite + vite-plugin-singlefile, and emits server type declarations.

Run

# HTTP transport (default, port 3001)
npm run serve

# Custom port
PORT=4000 npm run serve

# stdio transport (for Claude Desktop local config — see "Known Limitations")
npm run serve:stdio

# Dev mode (watch + serve)
npm run dev

The server listens at http://localhost:3001/mcp by default.

Configuration

Before deploying, update the Tally form ID:

1. Open src/mcp-app.ts

2. Replace the form ID constant with your real Tally form ID

3. Also update the data-tally-src URL in mcp-app.html to match

Testing with basic-host (local)

# Terminal 1 — run your server
npm run build && npm run serve

# Terminal 2 — clone and run the MCP Apps basic-host
git clone --depth 1 https://github.com/modelcontextprotocol/ext-apps.git /tmp/mcp-ext-apps
cd /tmp/mcp-ext-apps/examples/basic-host
npm install
SERVERS='["http://localhost:3001/mcp"]' npm run start
# Open http://localhost:8080

Testing with basic-host (against production)

To run the same harness against the deployed server instead of localhost:

SERVERS='["https://webweaver-nexus-mcp.vercel.app/mcp"]' npx tsx serve.ts

This is the most reliable end-to-end test — it exercises the full Vercel deployment, CSP propagation, sandbox iframe loading, Tally embed, and submit event flow.

Testing with MCP Inspector (quick smoke test)

MCP Inspector is Anthropic's official browser-based MCP debugger. It runs via npx (no install) and is the fastest way to verify that a server is reachable, tools list correctly, plain tools return expected output, and MCP App UI resources render correctly via the Apps tab.

npx @modelcontextprotocol/inspector

This opens a browser UI. Set:

• Transport Type: Streamable HTTP

• Connection Type: Via Proxy or Direct — both work for our server. Proxy routes JSON-RPC through Inspector's local proxy (port 6277); Direct goes browser → server. Either renders MCP Apps and honors the CSP correctly. Verified against Inspector v0.21.2.

• URL: http://localhost:3001/mcp (local) or https://webweaver-nexus-mcp.vercel.app/mcp (production)

Click Connect, then verify across tabs:

1. Tools — all 3 tools appear (join_waitlist, get_product_overview, get_contact_info); the two plain tools return their placeholder text when called.

2. Resources — ui://join-waitlist/mcp-app.html lists; reading it returns ~330 KB of bundled HTML.

3. Apps — select join_waitlist in the apps panel; the embedded Tally form renders inside its sandboxed iframe. Submit the form to verify the Tally pipeline end-to-end (form data POSTs to tally.so, configured notification emails fire).

Limitation — updateModelContext not observable in the UI: Inspector (as of v0.21.2) does not currently surface model-context updates that the app pushes back via appBridge.sendUpdateModelContext. The Tally render and submit flow are fully validated by Inspector, but to confirm the confirmation message actually fires into the host conversation, fall back to basic-host (which has a dedicated "Model Context" panel).

When to use which:

Exposing local dev to claude.ai (Cloudflare tunnel)

For iterating on the server locally against claude.ai's custom connector UI (which only accepts public HTTPS URLs, not localhost), expose your dev server via a Cloudflare tunnel:

# Terminal 1 — run the server
npm run build && npm run serve

# Terminal 2 — start the tunnel
npx cloudflared tunnel --url http://localhost:3001

Copy the https://*.trycloudflare.com URL from the tunnel output. In Claude's settings, add a custom MCP connector pointing to https://<tunnel-url>/mcp.

Note: As of writing, claude.ai's custom connectors ignore frameDomains declared in _meta.ui.csp (see GitHub issue anthropics/claude-ai-mcp#40). This will cause the Tally embed in join_waitlist to be blocked. The two read-only tools work correctly. Track that issue for the fix.

Deployment (Vercel)

The MCP server is deployed as a Vercel serverless function using the Express + Streamable HTTP pattern.

How it works:

• vercel.json routes traffic to api/mcp.ts, which exports the Express app as default.

• The Vite-bundled dist/mcp-app.html (the MCP App UI) is included in the deployment via includeFiles and read at runtime by server.ts via fs.readFile.

• The function runs on Vercel's Node.js 24 runtime with maxDuration: 60 (well above what's needed; tool calls return in milliseconds).

• No environment variables are required — all configuration is hardcoded in the source.

To redeploy: Push to the main branch. Vercel auto-deploys on push.

To verify the deployment:

# Sanity check — should return a JSON-RPC tools list (~880 bytes)
curl -X POST https://webweaver-nexus-mcp.vercel.app/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","method":"tools/list","id":1}'

# Resource read — should return ~330 KB of bundled HTML.
# A response under a few KB means the unbundled source HTML is being served
# instead of the bundled artifact (path resolution bug — see git history).
curl -X POST https://webweaver-nexus-mcp.vercel.app/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","method":"resources/read","params":{"uri":"ui://join-waitlist/mcp-app.html"},"id":1}' \
  | wc -c

For an interactive equivalent, run MCP Inspector against the deployed URL (see Testing with MCP Inspector above). Recommended as the first post-deploy check before bringing up basic-host.

Install in your MCP client

All clients connect to the same endpoint:

https://webweaver-nexus-mcp.vercel.app/mcp

Transport is Streamable HTTP. No authentication; all three tools are publicly callable.

Hosts that speak Streamable HTTP natively (claude.ai, ChatGPT, MCP Inspector, basic-host) take the URL directly. stdio-only hosts (Claude Desktop, Cursor today) use the mcp-remote npm shim — a small package that launches as a local stdio process and proxies JSON-RPC to the remote URL.

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows):

{
  "mcpServers": {
    "webweaver-nexus": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://webweaver-nexus-mcp.vercel.app/mcp"]
    }
  }
}

Restart Claude Desktop; the three tools appear in the tools menu.

The two read-only tools work in Claude Desktop. join_waitlist does not, due to the stdio cwd issue described in Known Limitations — this is a server-side path-resolution gap, not an mcp-remote problem.

claude.ai (Custom Connector)

claude.ai speaks Streamable HTTP natively — no shim.

1. Open Settings → Connectors (or Feature Preview → MCP, depending on rollout).

2. Add custom connector → paste https://webweaver-nexus-mcp.vercel.app/mcp.

3. Save.

The two read-only tools work. join_waitlist's Tally form is blocked by an upstream frameDomains bug — see Known Limitations.

Cursor

Edit ~/.cursor/mcp.json, or use Settings → MCP Servers in the Cursor UI:

{
  "mcpServers": {
    "webweaver-nexus": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://webweaver-nexus-mcp.vercel.app/mcp"]
    }
  }
}

Reload the Cursor window (Cmd+Shift+P → Reload Window).

ChatGPT

Available on plan tiers that support MCP / custom connectors.

1. Settings → Connectors (or Apps) → Add custom MCP server.

2. Paste https://webweaver-nexus-mcp.vercel.app/mcp.

3. Enable for a conversation.

Verifying the connection (any client)

Ask the host something like:

Use the WebWeaver Nexus connector to get the product overview.

If the tool fires and returns text, the wire is good. For join_waitlist, the embedded Tally form renders directly in the conversation on hosts that have shipped MCP Apps rendering (Inspector Apps tab, basic-host) — see the per-client caveats above for the others.

Known Limitations

Claude Desktop stdio integration is not currently supported

The two read-only tools (get_product_overview, get_contact_info) work in Claude Desktop. join_waitlist does not.

Cause: Claude Desktop launches MCP server processes with the working directory set to / (the filesystem root) on macOS. The current server.ts uses path.join(process.cwd(), "dist", "mcp-app.html") to locate the bundled HTML at runtime, which resolves to /dist/mcp-app.html under Claude Desktop — a path that doesn't exist. The cwd field in claude_desktop_config.json was tried as a workaround but is silently ignored on the version tested.

Workaround: Use a Streamable HTTP MCP host (basic-host, claude.ai's custom connectors when MCP App rendering bugs are fixed, or other spec-compliant clients) rather than Claude Desktop's local stdio mode.

Possible fixes for future work:

1. Embed the HTML as a build-time string constant. Replace the runtime fs.readFile with an import (or build step) that inlines dist/mcp-app.html directly into the compiled JS as a string. Eliminates filesystem path resolution entirely; works identically across every host environment. Cost: small build-step change; HTML changes require a rebuild (which they already do anyway).

2. A more robust path probe that tries dist/-prefixed paths first and never falls through to anywhere a same-named source file might live. The probe approach was attempted in commit e73484f and reverted in commit 32dc1aa. A Vite 8 → 7 downgrade was also tried in commit 2e33c8e (suspecting vite-plugin-singlefile incompatibility) and reverted in commit c8ad36d once we determined the actual cause was the path probe finding an unbundled source file on Vercel. See the git history around 28 April 2026 for the full diagnostic trail.

The first option is recommended if you come back to this.

claude.ai frameDomains bug

See note in the "Testing with Claude Desktop (Custom Connector)" section above.

Project Structure

├── api/ │ └── mcp.ts # Vercel serverless entry — exports Express app ├── main.ts # Local-dev entry — HTTP & stdio transports ├── server.ts # Tool & resource registration (shared) ├── mcp-app.html # App UI template (Vite entry, source) ├── src/ │ ├── mcp-app.ts # Client-side App lifecycle + Tally integration │ ├── mcp-app.css # App-specific styles │ └── global.css # Host variable fallbacks & reset ├── dist/ # Build output — function code + bundled mcp-app.html ├── vite.config.ts # Vite + singlefile plugin config ├── tsconfig.json # Client + shared type-checking ├── tsconfig.server.json # Server declaration emit ├── vercel.json # Vercel deployment config └── package.json

Version History

• v0.1.0 — First working production deployment. Three tools live; join_waitlist works on Streamable HTTP hosts. Claude Desktop stdio integration deferred (see Known Limitations).