NBB Annual Accounts MCP

Setup guide

ChatGPT

ChatGPT reaches MCP servers through developer-mode connectors: a URL, an authentication choice, and the tools appear in the conversation.

You need a key first. Your account page issues one — it starts with nbb_live_ and is shown once. If you have not signed up yet, sign in with your email address; the free plan needs no card.

Steps

  1. Open Settings → Connectors in ChatGPT.
  2. Under Advanced, switch on Developer mode. Custom MCP connectors live behind that flag and are not available on every plan.
  3. Choose Create (or Add custom connector).
  4. Name it nbb and paste the server URL: 
    https://test.nbb-mcp.be/mcp
  5. For authentication, pick the access-token / API-key option and paste your key. ChatGPT sends it as Authorization: Bearer <key>, which is exactly what this server expects.
  6. Save, then enable the connector in a new conversation's tools menu.

Developer-mode connectors are marked unverified and ChatGPT will ask you to confirm tool calls the first few times. That is the client being careful, not an error.

Reachability

Like claude.ai, ChatGPT connects from OpenAI's infrastructure. The URL has to be publicly reachable over HTTPS with a valid certificate; a local address will fail with a connection error no matter what the key says.

Check that it works

Start a new conversation and ask:

Find the annual accounts of Colruyt

The assistant should call search_company, find enterprise number 0400.378.485 (Etn. Fr. Colruyt NV), then call get_annual_accounts, poll get_operation once or twice, and read back a balance sheet with rubric codes.

It says it has no such tool

The connector is not loaded. Most clients only pick up MCP servers at start-up: restart it, and check the server is enabled in the client's tool list.

It reports 401 or "invalid API key"

The header is missing or the key is wrong. The value must be the whole key including the nbb_live_ prefix, after the word Bearer and one space. Keys are shown once — if you did not copy it, regenerate on your account page.

It gives up after one call and says it is still pending

get_annual_accounts is asynchronous: it returns an operation id and a poll_after_seconds. Tell the assistant to poll get_operation until the status is completed. The tool descriptions say so, but a smaller model sometimes needs the nudge.

Other clients