track

await cow.track({
  identifiers: { userId: "user_1" },
  event: "checkout_started",
  properties: { cartId: "c_9", total: 4200 },
});

Field	Required	Notes
identifiers	yes	Who the event is about. Creates the profile if it is new.
event	yes	Up to 200 characters. It may not start with system., which is reserved for the events Cowliss records itself.
properties	no	Any JSON object. Empty when omitted.
timestamp	no	ISO 8601 UTC, for a historical write. Never in the future.
messageId	on the wire	The dedupe key. The SDK generates one when you omit it.

Retries are safe

messageId is the dedupe key and travels as the Idempotency-Key header. Send the same one twice and the event is stored once. Derive it from the thing that happened (an order id, a request id), not a fresh random per attempt.

What one call does

One track, synchronously, before the response: the profile is resolved or created, traits merge, segments recompute, and any journey whose trigger matches starts.

Importing history is different, and quieter: see batch.