Idempotency keys are used to ensure that a request is processed only once, even if the request is sent multiple times.

Idempotency keys are useful when you want to make sure that a request is processed only once, even if the request is sent multiple times. For example, if you are creating a new subscriber, you want to make sure that the subscriber is created only once, even if the request is sent multiple times.

If you send a request to create a new subscriber with the same idempotency key, you'll get the same response as if you sent the request only once.

(Our implementation of idempotency keys is inspired by Stripe's idempotency keys.)

You can use idempotency keys for any request. To use an idempotency key, you pass the X-Idempotency-Key header with your request. The value of the header must be a randomly generated string of up to 200 characters such as a UUID.

Here's an example in cURL:

curl --request POST \
     --url https://api.buttondown.com/v1/subscribers \
     --header 'authorization: Token $BUTTONDOWN_API_KEY' \
     --header 'content-type: application/json' \
     --header 'X-Idempotency-Key: AaPYI03TpJgW7pgtPB09s' \
     --data '{ "email_address": "telemachus@buttondown.email", "type": "regular" }'

We can rerun the request with the same idempotency key and it will return the same response as if we sent the request only once.