Guides

How long an idempotency key stays valid, and what happens when it expires — You are storing idempotency keys and need to decide when to delete them.
How long a webhook signature stays valid: the replay window — Your webhook verification passes, but you need to know how old a request may be before you reject it.
The difference between HTTP 429 and 503, and which one you retry — Both statuses say come back later, and both are usually retried, but they mean different things and one of them is safe to repeat unchanged.
When an API returns 412 and when it returns 409 — Both statuses signal a conflict and the two are used interchangeably in the wild, but they answer different questions.
How much jitter to add to exponential backoff — Your backoff is doubling correctly but clients still retry in waves, and you need to know how much randomness to introduce.
Why */7 in a cron expression is not an even seven-minute interval — You scheduled a job with */7 in the minute field expecting it every seven minutes, and the gaps are uneven.
How many times a queue can deliver the same message — Your queue promises at-least-once delivery and you need to know the upper bound before designing around it.
How long an SSE connection stays open before something cuts it — Your server-sent events stream disconnects on its own and you need to know which layer is closing it.
How to make an API endpoint safe to retry — A request timed out and you cannot tell whether it succeeded. Retrying might create the charge twice; not retrying might lose it entirely.
HTTP 429 rate limits: how long to wait, and which limit is binding — Requests started coming back 429. You need to keep working without making the situation worse or losing the requests you already have queued.
How to verify a webhook signature correctly — You are receiving webhooks at a public URL. Anyone who learns that URL can post to it, and your handler creates records.
How to handle duplicate messages from an at-least-once queue — Your queue promises at-least-once delivery, so the same message can arrive twice. The consumer sends an email, and users are getting two.
Cursor or offset pagination: which one breaks and when — Users report seeing the same row twice while paging, or missing rows entirely, on a list that is being written to while they read it.
How to resolve a 409 or 412 write conflict without losing data — Your write was rejected with 409 or 412 because someone else changed the resource since you read it. Retrying blindly would overwrite their change.
What to do when an API key leaks — A key was committed to a public repository, pasted into a ticket, or printed in a log. It may already have been used.
SSE, WebSocket or polling: choosing a transport for live updates — You need to push updates to a client. Three transports are available and each is presented as the obvious answer somewhere.
How to keep coordinating agents in sync without replaying history — Several agents work the same effort from different machines. Every one of them reading the whole message history on every wake-up does not scale, and summarising independently makes them disagree.
How to run a long job without hitting request timeouts — An operation takes minutes. Doing it inside the request times out at the proxy, and the client has no way to find out whether it eventually finished.