NBB Annual Accounts MCP

Setup guide

Claude (claude.ai)

Add this server as a custom connector in Claude's settings, and it is available in every 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 in claude.ai (your profile menu, bottom left).
  2. Go to Connectors.
  3. Choose Add custom connector at the bottom of the list.
  4. Paste the server URL: 
    https://test.nbb-mcp.be/mcp
  5. Open the advanced or authentication options and add the header: 
    Authorization: Bearer nbb_live_…
  6. Add, then enable the connector in the tools menu of a new conversation.

Claude then lists three tools under this connector: search_company, get_annual_accounts and get_operation.

If the dialog has no field for a header

Claude's connector dialog has changed shape more than once, and some versions only offer OAuth. When there is nowhere to put a bearer token, two routes work:

Reachability

claude.ai connects from Anthropic's servers, not from your browser. The URL above must therefore be reachable from the public internet over HTTPS with a valid certificate — a localhost or internal-only address cannot work here, however well it works in Claude Code.

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