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Midplane is a gateway between AI agents and your Postgres databases. ChatGPT queries your data through it, never holds a connection string, and every statement it sends is checked against your policy before it runs. ChatGPT connects from OpenAI’s servers, so it reaches a gateway only at a public HTTPS URL. A gateway on a server with Docker or on a platform has one: its Midplane URL, through Midplane’s relay, with no tunnel, DNS record or open port. A gateway on this machine has none; to use a tunnel or a URL of your own instead, see hosted agents.
1

Copy the gateway's URL

On the project’s Agents page, under Connect an agent, pick ChatGPT and copy the URL, such as https://gw-7hq2m4xd.eu.midplane.app/mcp.
2

Add a custom MCP server

In ChatGPT on the web, open Plugins, select +, then Add custom MCP server. Name it Midplane, paste the URL as the Server URL under Connection, and choose OAuth for authentication. Read the risk warning, select I understand and want to continue, then Create as a plugin.Your workspace’s settings may not allow custom MCP servers: ask its admin.
3

Sign in and choose what it may reach

Install the plugin. ChatGPT opens Midplane: sign in, set each database to None, Read or Read + write, and Allow.
4

Try it

In a new chat, type @, pick Midplane, and ask which tables it can see. Its statement shows up in the project’s Query log.
You’re set: ChatGPT can answer questions from your data, and only what your policy allows runs. Masked columns stay masked, writes that need approval wait for a person, and every statement is in the audit log. Results go from your gateway to OpenAI, never through Midplane Cloud, and the relay can’t read them (what the relay sees).
ChatGPT asks you to confirm each query call, reads too, since the tool can write; it can remember your answer for the rest of the chat. list_tables and describe_table run without asking. To cut it off, Revoke it under Connected agents on the Agents page. It has to sign in again within 15 minutes.

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If it doesn’t work

  • ChatGPT can’t connect to the URL: check that the gateway’s setup step or Gateways page says Relay · connected, or see cannot reach the relay.
  • The consent page says it wants access, with no databases: you aren’t a member of the gateway’s project, or the URL isn’t registered. Ask an owner of the organization.
  • Through OpenAI’s Secure MCP Tunnel instead of the relay, signing in isn’t verified yet: see hosted agents.
Tested by apps/gateway/test/setup-relay.test.ts (a gateway behind a stand-in relay) and apps/gateway/test/auth.test.ts for the gateway’s side; the client’s steps by hand, through the relay.