ReplayFence

ReplayFence is a web app (with a lightweight gateway/sidecar) that detects and blocks API replay attacks and weak idempotency patterns in real time. It learns normal request uniqueness signals (idempotency keys, timestamps, nonce usage, signature headers) per endpoint and flags suspicious duplicates, time-skew anomalies, and token re-use across IPs/ASNs. It ships with SDK snippets to add idempotency keys and request signing to popular stacks, plus a dashboard that shows which endpoints are replay-prone and what to fix. This is not a full API security suite; it focuses narrowly on a common, expensive failure mode that many teams overlook until fraud or double-charging happens. It integrates with Stripe-like workflows, webhooks, and financial/booking APIs where idempotency and replay protection are business-critical.