@opencapstack/mcp-server

An MCP (Model Context Protocol) server for OpenCap Stack. Connect your cap table to Claude Desktop, Claude Code, Cursor, and any MCP-compatible client to manage stakeholders, share classes, SAFEs, dilution models, waterfall analyses, and financial reports — all through natural language.

Quick start

npx @opencapstack/mcp-server

The server reads your API key from the OPENCAP_API_KEY environment variable and starts on stdio by default.

Configuration

Claude Desktop

Add the following to your Claude Desktop config file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "opencap": {
      "command": "npx",
      "args": ["@opencapstack/mcp-server"],
      "env": {
        "OPENCAP_API_KEY": "your-jwt-token-here",
        "OPENCAP_BASE_URL": "https://api.opencapstack.com"
      }
    }
  }
}

Restart Claude Desktop after saving.

Claude Code

Add to your Claude Code MCP settings (.claude/settings.json or via claude mcp add):

{
  "mcpServers": {
    "opencap": {
      "command": "npx",
      "args": ["@opencapstack/mcp-server"],
      "env": {
        "OPENCAP_API_KEY": "your-jwt-token-here"
      }
    }
  }
}

Or from the command line:

claude mcp add opencap npx @opencapstack/mcp-server

Environment variables

| Variable | Required | Default | Description | |----------|----------|---------|-------------| | OPENCAP_API_KEY | Yes | — | Your OpenCap JWT token. Get one at https://api.opencapstack.com/api/v1/auth/login | | OPENCAP_BASE_URL | No | https://api.opencapstack.com | Base URL for the OpenCap API. Must NOT include /api/v1 (the tools add this automatically). Correct: https://api.opencapstack.com. Wrong: https://api.opencapstack.com/api/v1. If the suffix is present it will be stripped automatically with a warning. | | TRANSPORT | No | stdio | Transport mode: stdio or sse | | PORT | No | 3001 | Port for the SSE HTTP server (only used when TRANSPORT=sse) |

Available tools

| Tool | Description | |------|-------------| | list_stakeholders | List all stakeholders in the cap table | | get_stakeholder | Get details for a stakeholder by ID | | create_stakeholder | Add a new stakeholder | | update_stakeholder | Update an existing stakeholder | | list_share_classes | List all share classes | | get_share_class | Get details for a share class by ID | | create_share_class | Create a new share class | | list_equity_plans | List all equity plans | | get_equity_plan | Get details for an equity plan | | create_equity_plan | Create a new equity incentive plan | | list_safes | List all SAFE instruments | | get_safe | Get details for a SAFE by ID | | create_safe | Record a new SAFE | | update_safe | Update a SAFE (e.g. record conversion) | | list_documents | List cap table documents | | get_document | Get a document by ID | | search_documents | Search documents by keyword | | get_latest_valuation | Get the most recent 409A valuation | | get_valuation_history | Get the valuation history timeline | | create_valuation_request | Record a new valuation | | calculate_dilution | Model dilution from a new issuance | | get_fully_diluted_shares | Get fully diluted share count | | run_waterfall_analysis | Model exit proceeds distribution | | list_financial_reports | List financial reports | | get_financial_report | Get a financial report by ID | | create_financial_report | Generate a new financial report |

Self-hosted usage

If you run your own OpenCap Stack instance, set OPENCAP_BASE_URL to your instance's root URL (without the /api/v1 path -- the MCP tools add this automatically):

{
  "env": {
    "OPENCAP_API_KEY": "your-jwt-token",
    "OPENCAP_BASE_URL": "https://opencap.yourcompany.internal"
  }
}

Common mistake: Do not set OPENCAP_BASE_URL to https://opencap.yourcompany.internal/api/v1. The /api/v1 prefix is appended by each tool automatically. If you include it, all requests will use a doubled path like /api/v1/api/v1/.... The server will strip a trailing /api/v1 and log a warning, but it is best to set the correct value upfront.

SSE transport (web clients)

Start the server in SSE mode for HTTP-based MCP clients:

TRANSPORT=sse PORT=3001 OPENCAP_API_KEY=your-token npx @opencapstack/mcp-server

The server will expose:

• GET /sse — SSE connection endpoint
• POST /messages?sessionId=<id> — message endpoint

Security

Never hardcode your API key. Always pass it through environment variables.

• Do not commit .env files containing OPENCAP_API_KEY to source control.
• Rotate your API key regularly at https://app.opencapstack.com/settings.
• When using the SSE transport, run the server behind a reverse proxy with TLS and access controls.
• API keys are scoped to your account — treat them like passwords.

Development

git clone https://github.com/Open-Cap-Stack/opencapstack
cd packages/opencap-mcp
npm install
npm run build   # compile TypeScript
npm run dev     # run with tsx (no compile step)
npm test        # run Jest tests

License

MIT