Idempotency key
An idempotency key is an identifier associated with a logical operation that lets a service recognize repeated requests and prevent duplicate effects.
Think Distributed Systems
A client-supplied identifier that lets an API associate repeated requests with the same logical operation and return a consistent result.
- How it is used
- Prevents retries from producing repeated effects when request delivery is uncertain.
- How deep it goes
- Explains UUID assignment, retry reuse, transactional recording, uniqueness enforcement, and response reuse, but not implementation code beyond pseudocode.
- Examples
- Uses write-once registers, credit-card charges, airline ticket booking, reservation numbers, and Stripe API responses.
- What you can do after
- Apply idempotency keys to retryable payment or booking requests and reason about transactional receiver-side deduplication.
Read how Think Distributed Systems explains idempotency key →
Automating API Delivery
An idempotency key is a client-supplied identifier that lets an API detect and handle duplicate requests for an operation.
- How it is used
- Guides API design reviews for operations that must tolerate duplicate requests safely.
- How deep it goes
- Distinguishes naturally idempotent HTTP methods from operations requiring a key, without specifying key storage or implementation details.
- Examples
- Uses a POST payment endpoint to illustrate preventing duplicate server-side state changes.
- What you can do after
- Evaluate whether an API operation needs an idempotency key to handle duplicate requests.
Related concepts
- domain layerproduced by · A domain layer is an architectural part of an application that contains its domain concepts, rules, and behavior.
- operationconfigures · An operation is an action or computation performed by or through a system, object, or interface, often producing a result or effect.
- universally unique identifieruses · A universally unique identifier (UUID) is a standardized 128-bit identifier designed to distinguish entities with an extremely low probability of collision across independently generated values.
- GraphQLconfigured by · GraphQL is a query language and execution specification for APIs that lets clients request and manipulate data through a schema.
- endpointconfigures · An endpoint is a network-accessible address or interface through which a service exposes a resource or operation and handles requests and responses.
- replay attackaddresses · A replay attack is an attack in which previously captured valid messages, requests, or authentication data are retransmitted to produce an unauthorized effect.
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