Webhooks + Bastle

The gap this fills

Subscription analytics tools generally read data and stop there, which leaves you polling an API to find out that a customer cancelled. Outbound webhooks invert that: Bastle tells you. Because the events are derived after normalisation, they are the same shape regardless of which billing system produced them — a downstream service written against a Bastle cancellation event keeps working when you migrate processors.

Delivery semantics

Deliveries are enqueued when the underlying event is written and drained by a scheduled dispatcher. A failed attempt is retried after one minute, then five, then thirty, then two hours, then twelve, for six attempts in total across roughly fourteen hours. Delivery is at-least-once: a receiver that times out after processing may see the same event again, so key your handlers on the event id.

Verifying a delivery

Every request carries a signature header computed as an HMAC over the raw body with your endpoint's secret. Verify it against the raw bytes — not the re-serialised JSON, which may differ by whitespace or key order — and compare in constant time. A webhook receiver that skips verification is a public write endpoint for anyone who learns the URL.

Choosing what to subscribe to

Subscribing to everything is convenient and usually wrong: most receivers care about two or three types and will branch past the rest. Prefix wildcards are the middle ground when you want a whole family, such as every subscription event, without enumerating each one.