Registrum
Quickstart

Integration in 10 minutes

Follow these steps to go from zero to a working API call. All examples use Tesco PLC (company number 00445790) as the reference company.

1

Register and get your API key

~2 min

Enter your email to get a free API key. No credit card required. Your key arrives in your inbox within seconds.

No Companies House developer account needed — your Registrum key is the only credential required. Registrum handles the CH API on your behalf.

Free tier: 50 calls per month, all endpoints available. No credit card required. Your key looks like: reg_live_a1b2c3...

Tip: If you just want to explore, the Swagger UI at api.registrum.co.uk/docs lets you test every endpoint in the browser — just click Authorize and enter your key.
2

Make your first call

~3 min

Fetch an enriched company profile. We'll use Tesco PLC (00445790) as the example — a large, well-documented company with full accounts.

curl -H "X-API-Key: reg_live_YOUR_KEY_HERE" \
  "https://api.registrum.co.uk/v1/company/00445790"

Uses the demo key. Results are real data from the Companies House API.

3

Understand the response

~2 min

Every response is wrapped in an APIResponse envelope. Hover over the fields below to see what's enriched vs raw.

JSON response

{

"status": "success",

"cached": true, // served from cache — no CH API call made

"credits_remaining": 49, // your monthly quota remaining

"data": {

"company_name": "TESCO PLC",From CH API

"company_number": "00445790",From CH API

"company_status": "active",From CH API

"company_age_years": 78,Computed by Registrum

"accounts": { "overdue": false, "next_due": "2024-07-24" },overdue boolean computed

"sic_codes": ["47110"],From CH API

"cached": true,Infrastructure metadata

"credits_remaining": 49,Your quota remaining

}

}

Raw field
Passed through from Companies House API
Enriched field
Computed or derived by Registrum
Metadata
Infrastructure — caching, quota, request ID
4

Add financials

~2 min

The /financials endpoint parses the company's iXBRL filing and returns structured financial data — revenue, profit, net assets, employees — as clean JSON. No XBRL parsing required.

Financials are cached for 7 days. The response includes a data_quality object explaining exactly what was extracted and what wasn't available.

curl -H "X-API-Key: reg_live_YOUR_KEY_HERE" \
  "https://api.registrum.co.uk/v1/company/00445790/financials"
Example response (abbreviated)

{

"accounts_type": "full",

"period_end": "2024-02-24",

"profit_and_loss": {

"turnover": { "current": 68190000000 },// £68.19 billion

"profit_after_tax": { "current": 1400000000 }

},

"balance_sheet": { "net_assets": { "current": 10700000000 } },

"other": { "employees": { "current": 295622 } }

}

Financial data is only available for companies that file digitally. Micro-entities and dormant companies return limited balance sheet data only. See the financial data example →

5

Deploy to production

~1 min

Store your API key in an environment variable. Never hardcode it in source code or commit it to Git.

# Set the env var in your shell:
export REGISTRUM_API_KEY="reg_live_YOUR_KEY_HERE"

# Then use it:
curl -H "X-API-Key: $REGISTRUM_API_KEY" \
  "https://api.registrum.co.uk/v1/company/00445790"

Rate limits

Every response includes credits_remaining. A 429 response means you've hit the monthly limit or burst rate. Upgrade your plan to increase both.

Error handling

All error responses include status: "error" and a human-readable detail. On CH API outages, cached data is served with the X-Data-Stale header — your app stays live.

Director network

GET /v1/company/{number}/network?depth=1 returns all companies sharing directors. Depth 2 traverses one level further. Cached 24h.

curl -H "X-API-Key: reg_live_YOUR_KEY_HERE" \
  "https://api.registrum.co.uk/v1/company/00445790/network?depth=1"

Beneficial ownership (PSC)

GET /v1/company/{number}/psc returns the PSC register with decoded control types and active/ceased split. /psc/chain recursively traverses corporate entity PSCs to find ultimate beneficial owners. Each company resolved costs 1 credit.

# Flat PSC register (active/ceased split, decoded control types)
curl -H "X-API-Key: reg_live_YOUR_KEY_HERE" \
  "https://api.registrum.co.uk/v1/company/12345678/psc"

# Ownership chain — resolve to ultimate beneficial owners
curl -H "X-API-Key: reg_live_YOUR_KEY_HERE" \
  "https://api.registrum.co.uk/v1/company/12345678/psc/chain?max_depth=5"
See ownership chain example →

Ready to integrate?

Full API reference in Swagger — every endpoint, every parameter, try it live.

Open API docs →Upgrade plan
6

Use with AI (MCP)

~2 min

The Registrum MCP server lets you query UK company data directly from Claude Desktop, Cursor, and any other MCP-compatible AI client — no code required. Ask questions like "Who are the directors of Tesco and what other companies are they on?" and get live answers backed by Companies House data.

Add the following to your AI client config and restart it. Your Registrum API key is used for authentication — the same key you use for direct API calls.

// ~/.claude/claude_desktop_config.json
{
  "mcpServers": {
    "registrum": {
      "command": "npx",
      "args": ["-y", "@registrum/mcp"],
      "env": {
        "REGISTRUM_API_KEY": "reg_live_YOUR_KEY_HERE"
      }
    }
  }
}
search_companyFind companies by name — returns number, status, address
get_companyEnriched profile — age, SIC descriptions, overdue flags
get_financialsStructured P&L + balance sheet from iXBRL filings
get_directorsFull director history across all appointments
get_pscPSC register — decoded control types, active/ceased split
get_psc_chainOwnership chain — traverse corporate PSCs to find UBOs
get_networkCorporate network via shared director connections
Install via npx — no global install needed. The first run downloads the package automatically. Find it on npm: @registrum/mcp

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