Use Breakpoint Engine in ChatGPT

Breakpoint Engine connects to ChatGPT as a custom MCP connector. Once connected, ChatGPT can call the opm_* tools directly in your chat — estimate work, run OPM forwardsolves and backsolves, explain breakpoints, and step through interactive scenarios on a cap table you paste into the conversation.

Looking for a "Breakpoint Engine plugin"? ChatGPT plugins were retired by OpenAI; custom MCP connectors are the current mechanism. There is no marketplace listing to install — you add the connector by URL, below.

Requirements

• A ChatGPT plan with connectors and Developer mode (Plus, Pro, Business, Enterprise, or Edu).
• A Breakpoint Engine account with work-unit credits — create an account and buy a Round, Portfolio, or Practice pack.

Setup steps

1. Sign in at breakpointengine.com/account and purchase a credit pack (the connector meters work units against your balance; opm_schema and estimates are cheap, solves are metered).
2. In ChatGPT, open Settings → Connectors → Advanced and enable Developer mode. The option to add a custom connector only appears with Developer mode on.
3. Back in Settings → Connectors, choose Create (add a custom connector) and enter:
   • Name: Breakpoint Engine
   • MCP server URL: https://cloud.breakpointengine.com/mcp
   • Authentication: OAuth. Leave client ID and secret blank — the server supports dynamic client registration, so ChatGPT registers itself.
4. Complete the sign-in prompt (Auth0 — same account you purchased credits with).
5. In a new chat, enable the connector from the composer (Developer mode sources / tools menu), then ask ChatGPT to call opm_schema to confirm the connection.

First valuation in chat

1. Paste your cap table and assumptions in the documented JSON format — or describe your share classes in plain language and ask ChatGPT to build the JSON, then confirm it.
2. Ask for an estimate first: "Call opm_estimate for this cap table."
3. Then run: "Run opm_forwardsolve with max_work set from the estimate." For a backsolve from a recent round price, use opm_backsolve.

Troubleshooting

• No Create connector option — Developer mode must be on under Settings → Connectors → Advanced.
• OAuth / registration error — leave client ID and secret blank so ChatGPT can register dynamically; confirm you can sign in at /account with the same identity.
• Connection failed / 401 — re-authorize the connector; the OAuth token may have expired (tokens last about one hour and refresh on reconnect).
• insufficient_credits (402) — your work-unit balance is empty; buy another pack on account.
• Connector missing in chat — Developer mode must remain enabled; re-enable it under Settings → Connectors → Advanced.

Cap tables are never stored — computation, not custody. Also see Claude setup, Cursor setup, and the tool reference.