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How to Connect ChatGPT Desktop to NinjaTrader 8 with CrossTrade MCP

The ChatGPT desktop apps on macOS and Windows exposes MCP through Developer Mode + Apps & Connectors, the same mechanism as web. Important: the macOS desktop app cannot add MCP servers itself — register on web, and the connector syncs automatically. The Windows desktop app can add servers natively.

OAuth scope: mcp:readSingle-vendor host

Prerequisites

RequirementDetail
CrossTrade subscriptionElite
CrossTrade Add-Onv1.13.0 or higher
NinjaTrader 8Running, broker connected
AccountSim101 for first runs
OAuth scopemcp:read
Config file(Windows) Settings → Apps & Connectors → Advanced → Developer mode. (macOS) Cannot add directly: register on web.
CrossTrade MCP server
https://app.crosstrade.io/v1/api/mcp
Transport: streamable-http. Auth: OAuth 2.1 + PKCE. Request scope mcp:read. Read-only. Inspect accounts, orders, positions, journal, NinjaScript.

When to use Desktop vs Web vs Codex​

  • Desktop app: native, faster start, conversation lives locally. Same Apps & Connectors mechanism as web. Adding a new MCP server only works on Windows; macOS users register on web first.
  • Web: zero install. Adding a new MCP server works for everyone.
  • Codex CLI: terminal-based, edits local files. Best for NinjaScript work.

Path A — Windows desktop (add directly)​

  1. Open ChatGPT Desktop.
  2. Settings → Apps & Connectors → Advanced settings → toggle Developer mode on.
  3. Back on Apps & Connectors, click Create.
  4. Fill in:
    • Name: CrossTrade
    • MCP Server URL: https://app.crosstrade.io/v1/api/mcp
    • Auth: OAuth
  5. Save. Complete OAuth in the browser tab that opens.

Path B — macOS desktop (register on web, syncs in)​

The macOS app cannot add new MCP servers directly. Do this once:

  1. Open chatgpt.com in any browser.
  2. Follow the full ChatGPT web setup to add CrossTrade.
  3. Open ChatGPT Desktop on macOS. The CrossTrade connector now appears in the connector tray.

You only ever do step 1-2 once per ChatGPT account. The connector list is account-scoped, not device-scoped.

Step 2 (both paths): First read-only prompt​

In a new chat, enable CrossTrade in the connector tray below the message box, then:

Use read-only tools only. Confirm CrossTrade MCP is connected. List my accounts.
Summarize open positions, working orders, and add-on version.

The flow from here mirrors ChatGPT web. Same prompts apply.

FAQ​

Why can't macOS add servers directly?​

OpenAI hasn't shipped the Developer Mode "Create" UI to the macOS desktop app yet. As of mid-2026 it's documented as "web and Windows desktop." This may change.

Are MCP tools shared across web, Desktop, and iOS?​

Yes — connectors are scoped to your ChatGPT account, not the device. Sign in with the same account everywhere, see the same connectors everywhere.

Can I run mcp:trade from desktop?​

Same plan gating as web: only Business/Enterprise/Education plans expose write tools through ChatGPT MCP connectors.

OAuth handshake

The first tool call surfaces an authorization URL. Open it in a browser, approve mcp:read, and return to the harness. The access token is stored by the harness (keychain, config file, or memory depending on the client).

See CrossTrade MCP OAuth for the full flow, and 403/408 troubleshooting if the handshake fails.

Verify the connection

Smoke-test before doing anything stateful:

Call GetMcpCapabilities and McpSelfTest. Then ListAccounts and GetConnections.
Report add-on version, NT8 version, and which accounts are linked.
Read-only scope
You authorized mcp:read. The agent can inspect state but cannot place orders, deploy strategies, or write NinjaScript files.

Troubleshooting

SymptomLikely causeFix
403 insufficient_scopeToken authorized at mcp:read but tool requires mcp:tradeReauthorize the connection and select mcp:trade
OAuth callback failsSystem browser blocked the redirect or popupCopy the auth URL manually, complete it, paste the code back
Tools list is empty after connectServer registered but session did not refreshRestart the harness or trigger a tool list refresh
Add-on offline errorNT8 not running, or add-on not loadedConfirm NT8 is open and the CrossTrade add-on (v1.13.0+) is installed
Add Connector option missing on macOSmacOS desktop app does not expose Developer Mode for adding new serversAdd the connector on chatgpt.com in a browser; it syncs to the macOS desktop app automatically
Custom MCP write tools don't appear (Plus/Pro)Plus and Pro restrict custom MCP connectors to read/fetch-only toolsUpgrade to Business/Enterprise/Education

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