Each Dutch base registry has its own access route. Addresses and buildings (BAG) come through a REST API with an API key or as a bulk extract. The large scale topographic map (BGT) and the cadastral map are open data on the PDOK platform. Ownership data from the land registry (BRK) is mostly reserved for government bodies, and company data comes from the Chamber of Commerce (KVK) through subscription APIs.
Below you'll find what each registry holds, who may use what, how you connect, and which build choices matter around local copies, caching, and rate limits.
What the Dutch base registries are
The Netherlands runs a system of base registries, in Dutch basisregistraties. They are data collections with a legal basis, and public bodies with a statutory task are required to use them instead of asking citizens and businesses for the same data again. There are 10 base registries, from the personal records database to the subsurface registry.
Four of them come up in almost every application that deals with locations, property, or companies:
- BAG (Basisregistratie Adressen en Gebouwen), the register of addresses and buildings, including premises, units, and mooring and trailer sites. Municipalities supply the data and Kadaster, the Dutch land registry agency, runs the national facility.
- BRK (Basisregistratie Kadaster), the land registry with parcels, property rights, and who holds them.
- BGT (Basisregistratie Grootschalige Topografie), a detailed map of the country with buildings, roads, water, railways, and green space. Municipalities, provinces, water boards, and the rail infrastructure manager ProRail are among its sources.
- HR (Handelsregister), the business register kept by the Netherlands Chamber of Commerce (KVK), with companies, legal entities, and their branches.
According to developer.overheid.nl, the Dutch government's developer portal, the BAG alone is consulted more than 10 million times a day.
Querying Dutch base registries: an overview per registry
Access comes in three forms: individual queries through an API, open datasets and map services through PDOK, and subscriptions or deliveries that give you your own copy.
| Registry | Individual queries | Copy, download, or services | Who may use it |
|---|---|---|---|
| BAG | BAG API Individuele Bevragingen (version 2), BAG OGC Features API | BAG Extract in XML with monthly or daily changes, services on PDOK | Open data for everyone, API key through a request form |
| BRK | BRK Bevragen (version 2.0) | BRK Levering with change files, cadastral map as open data on PDOK | BRK Bevragen only for government bodies authorized to process citizen service numbers, cadastral map for everyone |
| BGT | BGT Features as an OGC API on PDOK | Full download from PDOK in GML | Open to everyone, mandatory for government |
| Business register | KVK APIs: Zoeken, Basisprofiel, Vestigingsprofiel, Naamgeving | Mutatieservice, Open Dataset Basis Bedrijfsgegevens | APIs by subscription, open dataset for everyone |
PDOK (Publieke Dienstverlening Op de Kaart) is the open geodata platform run by Kadaster. It offers map services, downloads, and OGC APIs, the web API standard of the Open Geospatial Consortium.
Addresses, buildings, and the map: BAG and BGT
The BAG API Individuele Bevragingen ("individual queries") is a REST API that returns near real time data as JSON. Version 2 lets you look up an address together with the objects linked to it, such as the unit and the building. Kadaster's usage guidelines are clear on scope: the API is meant for one or a few objects that you use right away, and it isn't meant for bulk retrieval. The limits are 50,000 queries per day and 50 messages per second.
If you need the whole register, use BAG Extract. It's a copy of the national data for one municipality or the entire country, delivered as XML files. A full monthly download appears on the 8th of each month, and subscriptions add monthly or daily change files. You can retrieve it through the Mijn Kadaster portal, automatically with an API key, or through SOAP services with a PKIoverheid certificate.
For the BGT, PDOK is the main entry point. The BGT Features OGC API returns objects by area or by identifier, in GeoJSON, JSON, JSON FG, or HTML. Each request returns at most 1,000 objects, with cursor pagination for the next batch. The API holds the complete BGT including history, and the data is refreshed daily before noon.
Property and company data: BRK and the business register
The BRK splits into an open part and a restricted part. The cadastral map, with boundaries, parcels, and parcel numbers, is open data under a CC BY license and is updated daily on PDOK, including as an OGC API. It shows no owners, and it isn't meant for exact measurements: boundary accuracy ranges from 10 cm to 80 cm depending on the quality label.
Ownership data sits behind BRK Bevragen. According to Kadaster, the API is currently available only to government bodies authorized to process the BSN, the Dutch citizen service number. Version 2.0 has been the standard since 14 September 2023, and Kadaster says the API won't be actively developed further in the coming period. For large volumes there's BRK Levering, a bulk delivery for government bodies and for organizations with a public interest and many properties. Use of this data comes with conditions, listed per product by Kadaster.
The KVK offers four APIs that work together. The Zoeken API (version 2) finds the KVK number, Basisprofiel returns core data and the list of branches, Vestigingsprofiel returns the details of one branch, and Naamgeving returns statutory and trade names. The Mutatieservice tells you what changed in the register. You pull those signals yourself, and they carry only metadata, so you fetch the details through the other APIs.
For analysis without company names, there's the Open Dataset Basis Bedrijfsgegevens. It covers only private and public limited companies (BV and NV), contains no personal data, and includes just the first two digits of the postcode. It's refreshed every working day and is available through an API and as a CSV file under CC BY 4.0.
Connecting: API keys, certificates, Digikoppeling, and FSC
Three connection patterns cover most cases.
- API key only. For the BAG API you request a key through a Kadaster form. PDOK's open APIs need no key.
- Subscription, agreement, and API key. For the KVK APIs you sign an agreement. Your organization must be registered in the business register and the signatory must be authorized to sign. The key goes in the header of each request, and a public test key lets you build before the contract is in place.
- Certificate and government identity. BRK Bevragen requires a valid PKIoverheid certificate, issued under the Dutch government's public key infrastructure, with an OIN, the identification number for government organizations, meeting the Digikoppeling requirements. You also need a Mijn Kadaster account and an API key issued after authorization.
Digikoppeling is the set of standards, maintained by the government agency Logius, that defines how Dutch public organizations exchange messages. It has included a profile for REST APIs since 2022. That profile uses Federated Service Connectivity (FSC) to manage access to APIs between organizations, and FSC version 2.0 is part of the Digikoppeling release of 21 April 2026. How this fits the layered architecture Dutch municipalities work with is covered in our article on the five layers of Common Ground.
Live queries or a local copy
The main design decision is whether your application queries the source at the moment of use or works from its own copy. Live queries suit a handful of objects per action, such as validating an address or fetching a company profile during an application. A local copy suits bulk processing and analytics. The BAG API explicitly excludes bulk use, so a nightly job over every address in a municipality belongs on BAG Extract.
After that, design four things on purpose:
- Caching. Store retrieved data with a fixed lifetime and keep the object's identifier, so you can refresh selectively later.
- Freshness. Decide per data element how much delay is acceptable. The BAG API is near real time, the BGT on PDOK updates daily, the KVK open dataset every working day, and the full BAG Extract download once a month. Daily change files or the KVK Mutatieservice tell you when your copy is out of date.
- Rate limits. Put a counter and a queue around each source's limits. That means 50,000 queries per day and 50 per second for the BAG API, at most 300,000 queries per month and 100 per second for the KVK APIs, and one query per minute per IP address for the KVK open dataset.
- Error handling. Tell an object that doesn't exist apart from a source that's temporarily unavailable. Retry timeouts and rate limit errors with increasing back off, and fall back to your cache where you can.
A dedicated integration component keeps keys, certificates, caching, and limits in one place. The basics of endpoints and error handling are in our article on API integration.
We've built custom software and integrations for more than 30 years, with 30+ engineers in Nijmegen and Sarajevo and 100+ projects delivered, certified for ISO 9001 and ISO 27001. That work includes a grant administration platform, MRO software for aviation, and RFID in the supply chain. Read how we approach software integration and API development, see the environments we work in on our government page, or get in touch to talk through your integration.
Frequently asked questions
What are the Dutch base registries?
The base registries, or basisregistraties, are data collections with a legal basis in the Netherlands, such as the BAG for addresses and buildings, the BRK for parcels and property rights, the BGT for the large scale map, and the business register for companies. There are 10 of them.
What is the difference between the BAG API and BAG Extract?
The BAG API Individuele Bevragingen is meant for one or a few objects that you use right away, with a limit of 50,000 queries per day. BAG Extract is an XML copy of the whole register or of one municipality, with monthly or daily change files. For bulk processing, BAG Extract is the right choice.
Can a private company query the BRK?
The cadastral map with parcels and parcel numbers is open data that anyone can use. BRK Bevragen, the API with ownership data, is currently available only to government bodies authorized to process citizen service numbers.
Do you need Digikoppeling or FSC to query base registries?
It depends on the source. The BAG API needs only an API key, PDOK's open APIs need nothing, and the KVK APIs work with a subscription and an API key. BRK Bevragen requires a PKIoverheid certificate with an OIN, following Digikoppeling.
