How to Calculate Webhook Deduplication TTL From Delivery Contracts, Not Guesswork

A technical guide published on DEV Community argues that idempotency key lifetimes for webhook deduplication should be mathematically derived, not arbitrarily chosen. The correct TTL is calculated by summing four measurable inputs: the provider's retry window, queue processing lag, clock skew allowance, and a manual replay grace period. Because retry windows vary significantly across providers — ranging from a few days to over a week — the same TTL should not be reused across different webhook senders. The article also warns against keying deduplication on the business resource itself, which can incorrectly block legitimate later changes to the same entity. Engineers are advised to trace every TTL value back to documented provider schedules and measured system metrics rather than relying on intuition.