Use Breakpoint Engine in Cursor and VS Code

Step-by-step setup for the two desktop agentic IDEs that speak MCP over HTTP: Cursor and VS Code (GitHub Copilot Chat). An advanced workflow for founders who keep scenario files, capitalization data, notes, and analysis in a local project while Breakpoint Engine computes in the cloud — same hosted endpoint, same Auth0 account, same opm_* tools; different config file shapes.

Jump to: Cursor · VS Code · Working pattern · Troubleshooting

Before you connect

Create an account (Auth0) and sign in.
Buy an Explore, Round, or Raise pack and confirm your work-unit balance on Account.
When the IDE opens Auth0, use the same identity that bought credits — wrong account → tools load then every call is 401 or 402.

Hosted endpoint (Streamable HTTP + OAuth): https://cloud.breakpointengine.com/mcp. Cursor and VS Code register themselves via dynamic client registration — the URL is all you need.

Cursor — setup

New to MCP in Cursor?

Where MCP lives: Cursor Settings → Cursor Settings → MCP (gear icon, or Cmd+Shift+J / Ctrl+Shift+J). Each server shows a status dot and, when connected, its tool list.
Project configs ask permission: opening a folder that contains .cursor/mcp.json prompts you to enable the project's MCP servers — click Enable. Missed it? Open MCP settings and flip the server toggle on.
Config changes need a reload: after editing mcp.json, click the refresh icon next to the server (or reopen the folder). Cursor does not hot-reload the file.
Tools run in Agent mode (Composer / Agent), not plain chat. By default Cursor asks before each tool call — approve, or enable auto-run for the session.

Steps

Add the server — pick one:
- Project — create .cursor/mcp.json in the folder you open in Cursor:
```
{
  "mcpServers": {
    "breakpointengine-cloud": {
      "url": "https://cloud.breakpointengine.com/mcp"
    }
  }
}
```
- Global — same JSON in ~/.cursor/mcp.json (available in every project).
- UI — Settings → MCP → Add new MCP server → type URL / HTTP → paste https://cloud.breakpointengine.com/mcp.
Reload MCP servers (refresh icon) or reopen the folder. Enable the project server if prompted.
When the server shows Needs authentication (or only exposes mcp_auth), click Connect — or ask the agent to run mcp_auth.
Complete Auth0 in the browser with the same identity used on /account.
Confirm tools appear (opm_schema, opm_estimate, …). In Agent mode, ask: “Call opm_schema on breakpointengine-cloud.”

Desktop OAuth uses the loopback callback http://localhost:8787/callback (some builds also use https://www.cursor.com/agents/mcp/oauth/callback). You do not put a redirect URI in mcp.json.

VS Code — setup (Copilot MCP)

Requires VS Code 1.101+, the GitHub Copilot and Copilot Chat extensions, and a Copilot subscription. MCP tools only run when the chat mode is Agent — plain Ask mode never calls them.

New to MCP in VS Code?

Servers must be started: after saving .vscode/mcp.json, a Start CodeLens appears above each server entry — click it. Or run MCP: List Servers from the Command Palette.
Trust prompt: the first start of a workspace-defined server asks you to confirm you trust it.
If nothing MCP-related appears, check chat.mcp.enabled is on and that VS Code is 1.101+.

Steps

Add to the workspace .vscode/mcp.json — note the top-level key is servers, not mcpServers:

{
  "servers": {
    "breakpointengine-cloud": {
      "type": "http",
      "url": "https://cloud.breakpointengine.com/mcp"
    }
  }
}

Or run MCP: Add Server → HTTP → paste https://cloud.breakpointengine.com/mcp → save to Workspace or User profile.
Click Start on the server (or MCP: List Servers → Start). Complete Auth0 when the browser opens. Leave any optional OAuth client ID empty.
Open Copilot Chat, switch the mode dropdown to Agent, then ask for opm_schema.

Working pattern

Keep your capitalization inputs, scenario files, and analysis in the project the IDE has open — the agent reads and writes them locally, and Breakpoint Engine performs the deterministic calculation in the cloud.

Prepare inputs in the capitalization input format (or describe the structure in plain language and let the agent draft JSON via opm_schema).
Call opm_estimate to preview the cost, then opm_forwardsolve / opm_backsolve. The gateway sizes the job, admits it against your balance, and caps the charge at its own quote.
Interactive round design: opm_scenario_begin → step / query / mutate / branch / diff → commit.

Full tool list: tool reference.

Troubleshooting

Cursor

Server not listed — project config not enabled; Settings → MCP, flip the toggle, or reopen the folder.
Stuck on Needs authentication / only mcp_auth — click Connect; allow the Auth0 browser popup; check View → Output → MCP Logs.
Config change ignored — refresh the server icon; Cursor does not hot-reload mcp.json.
Agent never calls tools — use Agent / Composer mode and ask for a tool by name (opm_schema).

VS Code

No tools in chat — switch Copilot Chat to Agent; confirm the wrench / tools menu lists the server.
Server never starts — click Start above the entry in mcp.json, or MCP: List Servers → Start → Show Output.
No HTTP server type — upgrade VS Code to 1.101+.

Both

OAuth or registration error — confirm you can sign in at /account; leave client ID/secret blank.
Tools load then every call is 401 — reconnect with the same Auth0 identity that holds credits.
402 / insufficient_credits — buy another pack on account, or shrink the job itself (re-seed equity_value closer on a backsolve, loosen tolerance) — the gateway sizes and admits every job on its own.

Also see ChatGPT setup, Claude setup, MCP overview, and the tool reference.