brreg

Brønnøysundregistrene — reading the register without being lied to

The API is open, keyless and unauthenticated. Fetching is not the problem. The problem is that every trap below returns a plausible number with HTTP 200 instead of an error, so a wrong answer looks exactly like a right one.

This skill is for the agent driving brreg-mcp-server (or its CLI). The tools carry these guards and fire them automatically — this file is why they exist and what to do when one speaks.

Surfaces

You are	Use
Claude Desktop	the .mcpb — four tools, guards always on
Claude Code / a script	brreg <verb> — the same handlers over argv

brreg get_units --orgnrs 923609016
brreg search_units --nace 96.210 --kommune 0301 --employees-min 1 --employees-max 4
brreg get_financials --orgnrs 918035443
brreg reference          # field glossary with statutory sources, retired NACE, role codes
brreg self-test --mock   # proves the install works offline

Always parse the JSON. stdout is one object per invocation (elapsed_sec included); diagnostics go to stderr; usage errors exit 2. Everything reproduces offline with --mock — the mock swaps the socket, not the code path, and its dataset is the trap set.

The rule that matters most

Never conclude from a zero, an absence, or a null without reading hints first.

The tools return hints precisely when the register is being quiet in a misleading way. A total: 0 with a retired_nace hint means "the code moved", not "no such businesses". If you report the zero, you have reported the trap's output as a finding.

What each silence actually means

You see	It does NOT mean	It means
total: 0	"none exist"	possibly a retired NACE code — SN2007 expired 2025-01-01, brreg serves SN2025. Read hints.
driftsinntekter: null + filed_no_revenue_line	zero revenue	a holding company — accounts filed, income sits in subsidiaries as financial income.
status: not_applicable	dormant / a red flag	an ENK (sole proprietorship). They never file. ~74% of the register.
antallAnsatte: null	headcount unknown	withheld — brreg never shows a value below 5 but holds the number.
gone (410)	not found	removed on legal grounds — brreg asks that caches drop it too.
deleted + slettedato	an error	dissolved — arrives as HTTP 200 with a reduced payload, straight into your success branch.