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Cursor Setup

Use this guide to put Arbitus between Cursor and your upstream MCP server.

Official Cursor MCP docs: https://docs.cursor.com/context/model-context-protocol

1. Start your upstream MCP server

For a local demo, use the included dummy server:

cargo run --bin dummy-server

For a real deployment, set transport.upstream in the policy to your MCP server URL.

2. Start Arbitus

Use the Cursor starter policy:

arbitus policy init cursor --out gateway.yml
arbitus gateway.yml

During local development from source:

cargo run --bin arbitus -- policy init cursor --out gateway.yml
cargo run --bin arbitus -- gateway.yml

This policy identifies Cursor by clientInfo.name: cursor, allows common read/search/edit tools, requires Human-in-the-Loop approval for edits, shadows command-like tools, redacts matching secrets, and logs every decision.

3. Add Arbitus to Cursor MCP config

Cursor supports project-scoped MCP configuration at .cursor/mcp.json and global configuration at ~/.cursor/mcp.json.

Create .cursor/mcp.json in your project:

{
  "mcpServers": {
    "arbitus": {
      "url": "http://localhost:4000/mcp"
    }
  }
}

If your Cursor version requires an explicit transport type for HTTP servers, use:

{
  "mcpServers": {
    "arbitus": {
      "type": "http",
      "url": "http://localhost:4000/mcp"
    }
  }
}

If Arbitus is protected by an API key, pass it as a header when your Cursor version supports headers for HTTP MCP servers:

{
  "mcpServers": {
    "arbitus": {
      "type": "http",
      "url": "http://localhost:4000/mcp",
      "headers": {
        "X-Api-Key": "${ARBITUS_AGENT_API_KEY}"
      }
    }
  }
}

4. Verify Cursor sees the gateway

Open Cursor settings or the chat tool list and confirm the arbitus MCP server is connected. Cursor's Agent can use MCP tools from the available tools list when relevant.

Run a safe tool first. Then test a blocked path using the Security demo.

Query audit events:

arbitus audit gateway-audit.db --agent cursor --limit 20

Production notes

  • Keep .cursor/mcp.json project-specific when the MCP tools belong to a single repo.
  • Use ~/.cursor/mcp.json only for personal cross-project tools.
  • Keep auto-run disabled for high-risk tools unless Arbitus policy requires approval or shadow mode.
  • Use the Arbitus policy as the source of truth; Cursor's UI toggles are useful, but the gateway enforces policy even if an agent guesses a tool name directly.