What is a postal code API?

A postal code API resolves a Dutch postcode and house number to the full address: street, city and municipality. It lets you autofill address forms and guarantees the address exists. The Companize Address Validation API does this through one endpoint that also supports free-text search and autocomplete.

How do I validate a Dutch address through an API?

Send the address (as postcode + house number or as free text) to the autocomplete endpoint. If the address exists you get the full, normalized address back. If it doesn't (say, a house number outside the range or on the wrong side of the street), you get an empty result.

Does the API support house-number suffixes?

Yes. Suffixes like 47A or 12-2 are recognized in the query and returned cleanly with the address.

Is the postal code API free?

Address validation is included with every paid Companize plan and isn't metered separately: address calls don't consume monthly credits.

How current is the postal code data?

The underlying Dutch postal code and street data is refreshed continuously, so new addresses and changes become available automatically.

Included with every paid Companize plan, no usage credits.

Postal code API & address validation for Dutch addresses

One endpoint that combines postal code lookup, address validation and address search. Resolve a postcode and house number to the full address, validate what your users type and autocomplete addresses; in milliseconds, as clean JSON.

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GET /v1/addresses/autocomplete? q=2513 AA 1 9 ms 200 OK

[
  {
    "postcode": "2513 AA",
    "houseNumber": "1",
    "street": "Binnenhof",
    "city": "Den Haag",
    "municipality": "'s-Gravenhage",
    "country": "NL"
  }
]

Try it yourself

Type a street, postcode or address and pick a suggestion to see the API response

Same response as GET /v1/addresses/autocomplete

Everything a postal code API should do

Built on current Dutch postal code and street data, with a purpose-built search index for predictably fast answers.

Postcode + house number lookup: Resolve a postal code and house number to the full address: street, city and municipality. "1012 LL 47" is all it takes for a complete, validated address.
Search by address string: No postcode needed: "Damrak 47 Amsterdam" resolves to the exact address. Search by street, city or any combination, typo-tolerant with prefix matching as you type.
Autocomplete for forms: Type a street or postcode and get concrete addresses as suggestions, ascending from the lowest house number. One pick by your user and the whole address is filled in.
Only real addresses: The API knows the house-number ranges per postcode AND the odd/even side of the street. A house number that doesn't exist simply returns nothing, so bad addresses never reach your database.
Suffixes and normalization: House-number suffixes like 47A or 12-2 are recognized and returned cleanly. Write postcodes however you like: "1012 ll" is normalized automatically.
Millisecond fast: A purpose-built search index answers in milliseconds, with predictable latency. Fast enough to query on every keystroke.

Frequently asked questions

What is a postal code API?: A postal code API resolves a Dutch postcode and house number to the full address: street, city and municipality. It lets you autofill address forms and guarantees the address exists. The Companize Address Validation API does this through one endpoint that also supports free-text search and autocomplete.
How do I validate a Dutch address through an API?: Send the address (as postcode + house number or as free text) to the autocomplete endpoint. If the address exists you get the full, normalized address back. If it doesn't (say, a house number outside the range or on the wrong side of the street), you get an empty result.
Does the API support house-number suffixes?: Yes. Suffixes like 47A or 12-2 are recognized in the query and returned cleanly with the address.
Is the postal code API free?: Address validation is included with every paid Companize plan and isn't metered separately: address calls don't consume monthly credits.
How current is the postal code data?: The underlying Dutch postal code and street data is refreshed continuously, so new addresses and changes become available automatically.

Other Companize APIs

Company Data API

Search by name or KVK number and get complete company profiles: legal form, status, trade names, activities, addresses and establishments. Everything from the register in one structured response.

Learn more

VAT Validation API

Validate a Dutch or EU VAT (BTW) number and resolve it to the company behind it. Confirm a customer's tax details at signup or checkout on verified numbers.

Learn more

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