Czech ARES register API by CompanyData

A small, typed TypeScript wrapper for looking up Czech company data from ARES (the Ministry of Finance business register): company names, full street addresses, phone, email, website, size and revenue, through one REST call.

This package is a thin convenience layer over the master @companydata/companydata-sdk. It is the same API and the same key, with the country pinned to the Czech Republic and a register-specific helper on top, so you can write client.getByIco("00177041") instead of assembling query parameters by hand.

One schema, one key. Every CompanyData register wrapper returns records in the same shape, so moving from ARES to another country's register is a one-line change.

At a glance

| | | | --- | --- | | Country | 🇨🇿 Czech Republic (countryCode: "CZ") | | Register | Czech ARES register | | Businesses in CompanyData | 3.51M | | With phone number | 341K | | With email address | 425K | | Lookup key | IČO (8 digits, leading zeros kept) | | Verified example | Škoda Auto a.s., 00177041 | | Live demo and comparison | companydata.com/ares-api | | Official register | ares.gov.cz |

Counts are from the live API on 2026-10-12 and grow over time.

What is ARES?

ARES (Administrativní registr ekonomických subjektů) is the Czech Ministry of Finance's register that aggregates the commercial register, trade register and other public sources. Its free API at ares.gov.cz returns the record for one IČO.

What the official ARES API does not give you: no phone number, no email address, no website, no employee or revenue figures, and no bulk filtering by city, industry or size.

CompanyData adds the missing fields. 3.51M Czech businesses with full addresses, phone, email, website, directors and firmographics, filterable and exportable in bulk through one live REST API. Comparison and a live lookup: companydata.com/ares-api.

Installation

npm install @companydata/ares-api

Get an API key at app.companydata.com/signup-api. Your first calls are free.

Quickstart

import { AresClient } from "@companydata/ares-api";

const client = new AresClient({
  auth: { type: "apiKey", apiKey: process.env.COMPANYDATA_API_KEY! }
});

// Look up one business by its IČO.
const company = await client.getByIco("00177041"); // Škoda Auto a.s.

// Search with filters (country is always CZ here).
const page = await client.search({
  cityName: "PRAHA",
  hasEmail: true,
  hasWebsite: true,
  page: 1,
  pageSize: 25
});
console.log(page.totalCount, page.records[0]?.["Company Name"]);

City and province names are UPPER CASE. Filter on cityName: "PRAHA", not "Praha" (which returns 0). The same goes for provinceName: "HLAVNÍ MĚSTO PRAHA". List exact names per country with GET /api/cities. Full field and filter reference: companydata.com/api-docs/request-company.

Run the full example against the live API with your key:

git clone https://github.com/companydatacom/ares-api && cd ares-api && npm install
COMPANYDATA_API_KEY=... npm run test:live

What a record looks like

Every record is a flat object with human-readable keys. This is Škoda Auto a.s. as returned by getByIco:

{
  "Company Name": "Skoda Auto A.S.",
  "Trade Name": "Skoda Auto a.s. - SAP Koncernove kompetencní centrum",
  "Company Registration Number": "00177041",
  "Address 1": "Tr. Vaclava Klementa 869",
  "Postal Code": "29301",
  "City": "Mladá Boleslav",
  "State/Province": "Hlavní Město Praha",
  "Country": "Czechrepublic",
  "Phone Number": "+4*****91",
  "Email": "*****@*****",
  "Website": "sou-skoda.*****",
  "Founding Year": null,
  "Employees Total": 0,
  "Yearly Revenue in U.S. Dollars": 0,
  "Business Category Code 1 - Description": "Motor Vehicles and Passenger Car Bodies",
  "Business Legal Type - Description": ""
}

Search is a preview, export is the full record. search (and the lookup helper, which uses it) returns about 20 fields with phone, email and website masked as *****, and does not spend credits. export, exportWithScroll and iterate return the full record (about 35 fields, unmasked contact details, SIC and national industry codes, legal status, group structure) and spend one credit per company you have not exported before. Which fields are on a record depends on your key's configuration. See the field reference and plans and credits.

Methods

| Method | Returns | Does | | --- | --- | --- | | client.search(params) | AresPage | Search Czech businesses with filters. | | client.getByIco(id, scope?) | CompanyRecord \| null | Fetch one business by IČO. scope adds extra filters when a number is not unique. | | client.export(params) | AresPage | Export one page of results (standard pagination). | | client.exportWithScroll(params) | AresScrollBatch | One scroll batch (max 50 records). Pass scrollId back in for the next. | | client.iterate(params, { maxRecords }) | AsyncGenerator<CompanyRecord> | Streams every matching record across scroll batches. | | client.raw | ApiClient | The underlying master SDK client, for anything not wrapped here. | | normalizeAresId(id) | string | The IČO normalisation the lookup helper applies. |

interface AresPage {
  records: CompanyRecord[];   // flat objects, keys like "Company Name", "City", "Email"
  totalCount: number;         // matches across all pages
  page: number;
  totalPages: number;
  pageSize: number;
}

interface AresScrollBatch {
  records: CompanyRecord[];
  scrollId: string | null;    // pass back in to get the next batch
  hasMoreRecords: boolean;
  pageSize: number;
}

params is the master SDK's filter set with countryCode removed, because it is always "CZ" here. For cross-border queries, use the master SDK directly.

Lookup by IČO

getByIco takes the 8-digit IČO (identifikační číslo osoby). Spaces are stripped and short numbers are left-padded with zeros, so "177041" and "00177041" match the same company.

Recipes

Find a company by name, pinned to a city

const { records, totalCount } = await client.search({
  search: "Skoda",
  cityName: "MLADÁ BOLESLAV",
  pageSize: 5
});

Build a segment: companies in a province with 50 or more employees

const page = await client.search({
  provinceName: "HLAVNÍ MĚSTO PRAHA",
  employeesTotal: { min: 50 },
  hasPhone: true,
  pageSize: 100
});

Stream a whole segment with scroll export

for await (const company of client.iterate(
  { cityName: "PRAHA", hasEmail: true },
  { maxRecords: 5000 }
)) {
  console.log(company["Company Name"], company["Email"]);
}

Drive the scroll loop yourself

let batch = await client.exportWithScroll({ cityName: "PRAHA", hasEmail: true, pageSize: 50 });
while (batch.records.length > 0) {
  process(batch.records);
  if (!batch.hasMoreRecords || !batch.scrollId) break;
  batch = await client.exportWithScroll({ cityName: "PRAHA", hasEmail: true, scrollId: batch.scrollId, pageSize: 50 });
}

Anything else: drop to the master client

const res = await client.raw.company.search({ countryCode: "DE", cityName: "BERLIN", pageSize: 10 });

Common filters

| Filter | Example | Notes | | --- | --- | --- | | search | "Skoda" | Free text over company and trade names. | | nationalId | "00177041" | Registration number. The lookup helper sets this for you. | | cityName | "PRAHA" | UPPER CASE. | | provinceName | "HLAVNÍ MĚSTO PRAHA" | Admin-2 name, UPPER CASE (the record's State/Province). | | postalCode | "29301" | Exact match. | | hasEmail, hasPhone, hasWebsite | true | Contact availability. | | employeesTotal, annualSales, foundingYears | { min: 50, max: 500 } | Range filters. | | sic4Digits | "7372" | 4-digit SIC industry code. |

Full list: companydata.com/api-docs/request-company.

Four ways to integrate

Pick whichever fits how you build. All four hit the same data behind the same key.

1. This register SDK (@companydata/ares-api): Czech lookups with a ARES-specific helper. You are here.
2. Master SDK (@companydata/companydata-sdk): all 200+ countries in one typed client, keyed by countryCode.
3. MCP server: connect an AI agent (Claude, Cursor and others) to https://companydata.com/mcp/ with your key in the x-api-key header. See companydata-mcp-server.
4. Raw REST: call GET https://app.companydata.com/api/company/search?countryCode=CZ&cityName=PRAHA with an x-api-key header. Contract: companydata.com/openapi.json.

curl -H "x-api-key: $COMPANYDATA_API_KEY" \
  "https://app.companydata.com/api/company/search?countryCode=CZ&nationalId=00177041&pageSize=1"

Error handling

Failed requests throw ApiError with the HTTP status. The client retries transient failures (429 and 5xx) with backoff before giving up.

import { ApiError } from "@companydata/ares-api";

try {
  await client.search({ cityName: "PRAHA" });
} catch (err) {
  if (err instanceof ApiError) {
    // 401: bad or missing key, 429: rate limited,
    // "Export credit limit exceeded" (code credits_limit_exceeded): export credits used up
    console.error(err.status, err.message);
  }
}

A scroll batch that is larger than your remaining credits is rejected as a whole, so keep pageSize small when a key is close to its limit.

All register wrappers

Same pattern, one per official register. Every wrapper returns the same record shape.

| Country | Register | Package | Lookup helper | | --- | --- | --- | --- | | 🇳🇱 Netherlands | KVK | @companydata/kvk-api | getByKvkNumber | | 🇩🇪 Germany | Handelsregister | @companydata/handelsregister-api | getByRegistrationNumber | | 🇬🇧 United Kingdom | Companies House | @companydata/companies-house-api | getByCompanyNumber | | 🇫🇷 France | Sirene | @companydata/sirene-api | getBySiret | | 🇧🇪 Belgium | KBO/BCE | @companydata/kbo-api | getByEnterpriseNumber | | 🇵🇱 Poland | KRS | @companydata/krs-api | getByNip | | 🇸🇪 Sweden | Bolagsverket | @companydata/bolagsverket-api | getByOrgNumber | | 🇨🇭 Switzerland | Zefix | @companydata/zefix-api | getByUid | | 🇨🇿 Czech Republic | ARES | @companydata/ares-api | getByIco | | 🇩🇰 Denmark | CVR | @companydata/cvr-api | getByCvr | | 🇧🇷 Brazil | CNPJ | @companydata/cnpj-api | getByCnpj | | 🇦🇺 Australia | ABR | @companydata/abn-lookup-api | getByAbn | | 🇺🇸 United States | SEC EDGAR | @companydata/sec-edgar-api | getByRegistrationNumber |

Plus the master SDK for every other country: @companydata/companydata-sdk.

License

MIT. Built and maintained by CompanyData.com.