Documentation

Three tools, synchronous calls, a stable set of error codes.

Connecting

Endpoint	`https://test.nbb-mcp.be/mcp`
Transport	MCP streamable HTTP (one endpoint, POST + SSE). Not the deprecated two-endpoint SSE transport.
Authentication	`Authorization: Bearer nbb_live_…` on every request
Session	Stateful: the server expects the normal `initialize` handshake.

The client-by-client setup guide is on your account page, next to your key. A request without a key gets 401 with a WWW-Authenticate header; a key over the rate limit gets 429 with Retry-After.

Tools

`search_company` billable

Resolve a company name to its Belgian enterprise (KBO/BCE) number, or list the names registered for a number.

Parameter	Type	Required	Description
`query`	string	yes	A name, part of a name, or an enterprise number in any notation (0403.170.701, BE0403170701, 403170701). Typo-tolerant and language-agnostic; numbers bypass the fuzzy search.
`language`	string	no	nl, fr, de or en. Only orders the returned names; filters nothing out.
`limit`	integer	no	How many companies to return. Default 10, maximum 25.

Returns. Candidates best match first: kbo_number, every registered name with its type and language, and match_score (1.0 for a direct number hit). Plus warnings[], which explains an empty result or a failed mod-97 check digit.

`get_annual_accounts` billable

Fetch the annual accounts a company filed with the NBB: balance sheet, income statement, appropriation of results, social balance sheet and notes, each line with its official rubric code and a translated label.

Parameter	Type	Required	Description
`kbo_number`	string	yes	Belgian enterprise number in any notation. Not the name — call search_company first.
`year`	integer	no	The calendar year the accounting exercise ends in. Omit for the most recent filing.
`language`	string	no	Label language: nl, fr, de or en. Default nl. Figures are identical in every language.

Returns. The accounts in the same call: status "completed" with the parsed filing in result, plus cached: true when it was served from cache. A request that cannot be served returns status "failed" with a stable error {code, message}.

`check_xbrl_availability` billable

List every annual account a company filed with the NBB and whether each is machine-readable (XBRL) or a PDF-only image — the years get_annual_accounts can serve.

Parameter	Type	Required	Description
`kbo_number`	string	yes	Belgian enterprise number in any notation. Not the name — call search_company first.
`year`	integer	no	Restrict the list to one financial year. Omit to list everything the company ever filed.

Returns. Filings newest first, each with fiscal_year, reference_number, model_type, deposit_type, deposit_date and xbrl_available. xbrl_available true means get_annual_accounts serves it as structured data; false means the NBB holds only a PDF.

How long a call takes

get_annual_accounts answers in the call itself: fetching a filing means calling the National Bank, downloading the deposit and parsing XBRL, and all of that happens while your client waits.

A fresh filing usually takes a few seconds, occasionally up to a minute when the National Bank is slow. Wait for the answer rather than retrying — a retry is a second billable call for the same work.

A filing that has been fetched before comes back instantly with status: "completed" and cached: true. Results are cached per deposit and never expire, because a filed annual account is immutable — a correction is a new deposit with its own reference, and that is what the server picks up.

Error codes

A failed get_annual_accounts call carries error.code, and these strings are stable — a client may branch on them.

Code	Meaning	What to do
`no_accounts_found`	The NBB has no accepted filing for this company, or none for the year you asked for. The message lists the years that do exist.	Retry with one of the years from the message, or tell the user there is nothing to show. Retrying the same request will not help.
`pdf_fallback_required`	The filing exists but only as a PDF (older or non-standardised deposits), or in a taxonomy version this server cannot map yet.	Reading PDF filings with an LLM is in progress and not yet available. Call check_xbrl_availability to find the years that are machine-readable, and tell the user the filing exists but cannot be read yet.
`nbb_unavailable`	The National Bank's service was unreachable or answered 429/5xx after our own retries.	Transient. Retrying in a few minutes is worth it — this is the one code where that is true.
`nbb_error`	The NBB answered, but with something unusable (a 4xx that is not a missing format).	Do not retry. Report the message; if it repeats for a company that should have accounts, it is a bug on our side.
`deposit_unreadable`	The deposit downloaded but could not be parsed as XBRL.	Asking the same question again is reasonable; if it keeps failing, the filing itself is the problem.
`nbb_not_configured`	This instance has no NBB subscription key configured.	Nothing a client can do; it means the deployment is incomplete.

Errors that are not failed calls

Bad input and an exhausted quota come back as a tool error (MCP isError: true) with an explanatory message rather than as a failed result — there is nothing with a stable code to branch on, only something for the model to fix or report.

Situation	Response
Monthly quota reached	Tool error naming the limit and where to upgrade (`/pricing`). The refused call itself is recorded but not charged.
Filing exists only as a PDF	The call fails with `pdf_fallback_required`: reading PDF filings with an LLM is in progress and not yet available. `check_xbrl_availability` shows which years are machine-readable.
Not a valid enterprise number	Tool error naming the problem and suggesting `search_company`.
Missing or invalid API key	HTTP `401` before MCP sees the request.
Too many requests	HTTP `429` with `Retry-After`, at 30 requests per minute (burst 10) per key.

Limits

Limit	Value
Requests per minute per key	30
Burst	10

There is no monthly quota in force during the alpha: calls are counted, never refused. The per-key rate limit above stays, because it protects the data source rather than revenue. The quotas that apply at launch are not decided yet.

The result JSON

Every completed get_annual_accounts result has the same shape:

Field	Contents
`meta`	Identifiers, filing and response language, model type, taxonomy version, `data_source`, `confidence`, `caveats`, and the current and previous period dates.
`identification`	Name, address and legal form as filed.
`statements[]`	Stable ids `balance_sheet_assets`, `balance_sheet_liabilities`, `income_statement`, `appropriation`, `social_balance`; rows are `{code, label, level, current, previous}`.
`notes[]`	The note sections of the filing, same row shape.
`unmapped_facts[]`	Facts we could not tie to a rubric code. Never empty out of laziness and never silently dropped — if something is missing from the statements, it is here.

Languages

language accepts nl, fr, de and en, and defaults to nl. Labels come from the National Bank's own taxonomy label linkbases, not from a translation engine, so they match the wording on the official forms.

If a label is missing in the language you asked for, the response falls back in order: requested language → the language the filing was submitted in → nl → fr → en. The figures never change with the language, and meta.response_language tells you what you actually got.

The website itself is published in Dutch, French and English. It follows your browser's language preference; the switcher in the navigation overrides it for the page you are on, and nothing about that choice is stored.

Data sources and caveats

meta.data_source says how a result was produced, and it is the field to read before trusting a number:

`data_source`	What it means	Confidence
`xbrl`	Parsed from the XBRL instance the company filed. Figures and rubric codes are exactly what was deposited.	Authoritative
`pdf_llm`	Reserved for filings read from a PDF by an LLM into the same JSON shape. That feature is in progress: no result carries this value today, and a PDF-only filing fails with <code>pdf_fallback_required</code> instead.	Heuristic — `meta.confidence` will carry a balance-check score and `meta.caveats` will say the numbers were read from a document.

Known caveats

Only filings the National Bank has accepted are served. A deposit that was corrected later resolves to the correction, not the original.
Company-name search uses the KBO/BCE open-data denomination file, refreshed monthly. A company registered in the last few weeks may be findable by number before it is findable by name.
Several companies can share a name. search_company returns candidates with a match score and expects the caller to disambiguate rather than guess.
Older filings use earlier taxonomy generations. Where a generation is not yet mapped, the response says so (pdf_fallback_required) instead of returning partial figures.
This service is not affiliated with the National Bank of Belgium and adds no interpretation: what is filed is what you get, including any errors the filer made.