Glossary term
What is idempotency key? Meaning for developers
In Backend in Depth
A unique value the client sends with a POST. If the request is sent again, the server sees the key and returns the first result. It does not repeat the work.
Learn it properly · Backend in DepthLesson 2: REST API Design Best Practices: Resources, Versioning, Status CodesNouns, not verbs. One error format. Ways to version an API. Idempotency keys for POST, and partial updates.In Full-Stack Questions
A unique value sent with a request so repeating it does not repeat the action, such as a second payment.
Learn it properly · Full-Stack QuestionsLesson 13: Popular Libraries Interviewers Ask AboutTanStack Query, Zustand, Zod, React Hook Form, auth libraries, Redis, BullMQ, Stripe, testing tools and more.In API Design
A unique value the client sends with a POST so the server can recognise a retry and not do the work twice.
Learn it properly · API DesignLesson 5: Idempotency Keys, Retries, Webhooks and Rate LimitsSafe retries with idempotency keys, webhooks with signatures and retries, rate limit headers, and long-running jobs.In Observability & SRE
A unique id sent with a request so the server can spot a repeat and not do the work twice.
Learn it properly · Observability & SRELesson 7: Reliability Patterns: Timeouts, Retries, Circuit Breakers and Graceful DegradationFailure modes, timeouts and retries with backoff, circuit breakers, bulkheads, load shedding, tested with fault injection.