Documentation

Cursor

Cursor can connect to Northsun (formerly Mnemix) as a custom remote MCP server. Add the endpoint to a global or project mcp.json, interpolate MNEMIX_API_KEY into the authorization header, restart the relevant Cursor process, and verify a read-only tool. This is protocol interoperability, not an official Cursor partnership or a promise that every Northsun MCP schema is frozen.

Prerequisites

A Cursor version that supports remote Streamable HTTP MCP servers.
A Northsun API key available to the Cursor process as MNEMIX_API_KEY.
A controlled test caller already present in the Northsun tenant.

Cursor documents two configuration scopes:

Project: .cursor/mcp.json
Global: ~/.cursor/mcp.json

Use project scope when the connection belongs to one repository. Use global scope only when the same tenant and key should be available across projects.

Configure the remote server

Set the environment variable before launching Cursor, then add:

{
  "mcpServers": {
    "mnemix": {
      "url": "https://mcp.mnemix.ai/mcp",
      "headers": {
        "Authorization": "Bearer ${env:MNEMIX_API_KEY}"
      }
    }
  }
}

Cursor's envFile setting applies to local stdio servers, not remote HTTP servers. For a remote server, its official configuration uses environment interpolation in headers. Ensure the desktop or CLI process actually inherits the variable; a variable visible in one shell is not automatically visible to an app launched elsewhere.

Verify the connection

Restart Cursor or reload the MCP configuration.
Open Customize and confirm the mnemix server is enabled.
In Agent, inspect Available Tools for Northsun tools.
Ask Agent to call caller_lookup for an existing controlled test number.
Expand the tool result and confirm the request reached the expected tenant.

Cursor asks for tool approval by default. Keep approval enabled while validating the connection so you can inspect the tool name and arguments before execution.

Common failures

Symptom	Likely cause	Fix
Literal `${env:MNEMIX_API_KEY}` reaches the server	The Cursor process cannot see the variable or is stale	Launch Cursor from an environment that exports the variable, then restart it.
`401 unauthorized`	Header interpolation failed or the key is invalid	Inspect MCP logs and verify the environment without printing the key.
Server is absent from Available Tools	Wrong config scope, malformed JSON, or disabled server	Check both supported `mcp.json` locations and the Customize panel.
Connection works in the IDE but not another Cursor surface	The surfaces are loading different environment or policy settings	Verify that surface independently; do not infer parity from the IDE.
Tool schema differs	Northsun MCP changed independently of REST	Inspect the current tool entry and follow its live schema.

Cursor's official troubleshooting path is Output → MCP Logs. Use those logs for connection and auth errors, but do not paste logs publicly until secrets and caller data are redacted.

Remove the connection or rotate the key

Delete the mnemix entry from the relevant mcp.json, then restart Cursor. If the key was ever hardcoded or exposed, revoke or rotate it in Northsun and update the environment before re-adding the server. Deleting the JSON entry does not invalidate the credential.

Stable and beta boundaries

Northsun's frozen public REST surface is documented in the API reference. The remote MCP server also exposes broader contact and governed-context tools; those schemas evolve separately and should be rechecked in Cursor after an upgrade. Connecting the server does not ship Beacon or guarantee proactive context injection.

This page documents a custom MCP connection. It does not claim marketplace listing, native integration, certification, partnership, or support from Cursor.