Developers

Build with UK company data

The CompanyStack API returns the Companies House register, figures from filed accounts, owners and health scores as JSON. The free plan gives 1,000 requests a day, with no card.

Try a live request, no sign-up Get a free API key

Tools

API reference Every endpoint with its parameters, the plan it needs and an example response, from the OpenAPI description.
Call the API from your code Copyable JavaScript and Python examples over plain HTTPS, with authentication, retries on 429 and paging.
MCP for SI agents Connect Claude, Cursor and other SI agents to the hosted MCP server at api.companystack.co.uk/mcp: nothing to install, just your API key.
Google Sheets, Excel and Chrome Formulas such as =COMPANYSTACK_STATUS(A2) for spreadsheets, and a Chrome extension that checks any company you select on a page.
Postman and collections Every request ready to run in Postman, Bruno or Hoppscotch, with an environment for your API key.