Capacities MCP Worker

A Cloudflare Worker that wraps the Capacities API as a remote MCP server. Connect Claude on any device -- iPhone, web, desktop, Claude Code -- to your Capacities knowledge base.

Why this exists

The community capacities-mcp package runs locally (stdio transport). That works for Claude Code and Claude Desktop, but not for claude.ai (web) or Claude on iOS/Android, which require a remote MCP server over HTTPS.

This Worker is that remote bridge.

Related MCP server: D&D Combat MCP Server

Architecture

Claude (web / iOS / Desktop / Code)
    |
    | HTTPS (Streamable HTTP or SSE)
    v
CF Worker (this project)
    |
    | HTTPS + Bearer token
    v
Capacities API (api.capacities.io)

Setup

1. Prerequisites

• Capacities Pro subscription ($8/mo) with API key

• Cloudflare account (free tier is enough)

• Node.js 18+ and npm

2. Clone and install

cd capacities-mcp-worker
npm install

3. Set your Capacities API key as a secret

npx wrangler secret put CAPACITIES_API_KEY
# paste your key from Capacities Settings > API

4. Deploy

npm run deploy

Wrangler prints your URL, e.g.: https://capacities-mcp.<you>.workers.dev

5. Test

curl https://capacities-mcp.<you>.workers.dev/health
# {"status":"ok","service":"capacities-mcp"}

6. Connect Claude (web + iOS)

1. Go to https://claude.ai

2. Settings > Connectors > Add Custom Connector

3. Name: "Capacities"

4. URL: https://capacities-mcp.<you>.workers.dev/mcp

5. Save

The connector syncs to your iPhone Claude app automatically.

7. Connect Claude Desktop (optional, alternative to local capacities-mcp)

Add to your Claude Desktop config:

{
  "mcpServers": {
    "capacities": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://capacities-mcp.<you>.workers.dev/sse"]
    }
  }
}

8. Connect Claude Code (optional)

claude mcp add capacities \
  --transport sse \
  --url https://capacities-mcp.<you>.workers.dev/sse

Or keep using the local capacities-mcp package for Claude Code (faster, no network hop).

MCP Tools

Example prompts

• "List my Capacities spaces"

• "Save this to my daily note: learned about Cloudflare R2 today"

• "Create a page called 'Ito's Lemma' with tags quant-finance and math"

• "Search for notes about stochastic calculus"

• "Save this URL to my research space: https://example.com/paper"

Security

• The Capacities API key is stored as a Cloudflare Worker secret (encrypted)

• The Worker does not add its own auth layer (the MCP endpoint is public)

• If you want to restrict access, add Cloudflare Access or a bearer token check in the fetch handler (see comments in index.ts)

To add a simple bearer token gate, set a secret:

npx wrangler secret put MCP_AUTH_KEY

Then uncomment the auth check in src/index.ts.

Limitations

• Capacities API cannot read full object content (search returns IDs/titles only)

• Rate limited to 120 requests per 60s per endpoint

• API is beta and subject to change

Cost

• Capacities Pro: ~$8/mo

• Cloudflare Worker: $0 (free tier: 100k requests/day)

• Durable Objects: $0 for low usage