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API and developers

API keys and authentication

Create, regenerate and revoke API keys on the API keys page. Send your key in the Authorization or X-Api-Key header. A key is shown only once.

Your first key

When you sign up, we create a first API key called "Default" on the API Free plan. No card is needed.

Create, regenerate or revoke keys

Go to API keys.

  • Create key: give the key a name, such as the app or environment it is for.
  • Regenerate: issues a new key with the same name. The old key stops working at once.
  • Revoke: switches the key off. Apps using it get a 401 error.

We show the full key only once. We store only a fingerprint (hash) of it, so we cannot show it again. If you lose a key, regenerate it.

API planActive keys
Free3
Starter5
Business10
Enterprise25

All keys on an account share the same plan limits. Splitting work across keys does not give you more requests.

Sending your key

Keys start with cs_. Send yours in either header:

Authorization: Bearer cs_your_key
X-Api-Key: cs_your_key

The base address is https://api.companystack.co.uk. For example:

curl -H "Authorization: Bearer cs_your_key" https://api.companystack.co.uk/company/00445790

Keys cannot be sent in the address (query string).

Keep keys secret

  • Do not put keys in browser code, mobile apps or public code repositories.
  • Store them in environment variables or a secrets manager.
  • If a key may have leaked, regenerate or revoke it straight away.

Every time a key is created, we email you. If you did not create it, revoke it and tell us.

Documentation

The website and the API are separate

Using the website never uses API requests. The web app plan and the API plan are separate subscriptions. See Plans and prices compared.

Last updated 2 October 2026

Still need help? Contact us, or if you have an account, open a support request.