Technology architecture - Concept
Idempotency
Designing an operation so repeating it does not accidentally repeat the effect
What's it for?
Makes repeated requests safe by ensuring the same action is not accidentally carried out more than once.
For example…
A payment API uses an idempotency key so retrying the same request after a timeout does not charge the customer twice
A job that marks an invoice as sent is idempotent if running it twice leaves the invoice in the same final state rather than sending two copies.