sandbox/test API key

Your sandbox API key is in your account under **API** settings — go to https://tinytax.co.uk/profile/api and you'll find both your test key (prefixed `tt_test_...`) and live key listed there.

The test key is what you want for sandbox development — it's free, unlimited, and doesn't submit anything to HMRC or Companies House. You can make real API calls and get realistic responses without affecting any live filings.

If you only see a live key and no test key in that section, just reply here or drop us an email at [email protected] and we'll get a test key activated on your account.

For full details on authentication and the difference between test and live keys, see the [Developer API: Authentication guide](https://tinytax.co.uk/support/developer-api-authentication).

The sandbox key has the prefix `tt_test_...` — it lets you make submission requests and get realistic responses without actually filing anything with HMRC or Companies House, and it's free with no impact on your Portfolio allowance.

Check the **API** section of your account at /profile/api. Your test key should appear there alongside the live key. If only the live key is listed (no `tt_test_...` entry), the test key hasn't been activated on your account yet — reply here and we'll enable it for you.

Quick summary of the difference:

| | Test key (`tt_test_...`) | Live key (`tt_live_...`) |
|-|--------------------------|--------------------------|
| Reaches HMRC / Companies House | No | Yes |
| Submissions stored | No (stateless) | Yes |
| Counts toward allowance | No — free, unlimited | Yes (20/year on Portfolio 3) |

More detail on test vs live keys and authentication in general: https://tinytax.co.uk/support/developer-api-authentication

Hi James,

Thanks for the nudge on this — you spotted a real gap. We've just shipped self-serve test keys.

Head to https://tinytax.co.uk/profile/api and you'll see two cards: Live (which you already have) and Test. The Test card has a Generate Test Key button — clicking it issues a fresh tt_test_… key. It's shown once at the top of the page, so copy it somewhere safe before navigating away. After that the key ID stays visible on the card and you can rotate it any time.

Using a tt_test_… key automatically puts the API into sandbox mode — full validation, no real HMRC/Companies House calls, no charges, and the magic company numbers documented at https://tinytax.co.uk/developers/sandbox give you deterministic outcomes (accepted / rejected / errored). Both key types hit the same production endpoint, so you don't need to switch base URLs.

Any trouble generating it, just reply here.

If you have any further questions, just reply to this email.

Best regards,
Alex
TinyTax Support