idempotencyKey.

evaluate and evaluateDetails require idempotencyKey: a caller-owned id for one logical evaluation. Generate it once per evaluation with crypto.randomUUID().

If a request's outcome is uncertain (a timeout, a dropped connection), resend it with the same key. The platform deduplicates the Exposure, so the subject is counted once. This is why the SDK refuses retries: an automatic retry with a fresh key is a second Exposure for one logical evaluation, and it double-counts the subject in every experiment reading that Flag.

The key is yours, not ours. Deriving it from something stable in your own request context (a request id, a job id) makes retries idempotent by construction.

• IDEMPOTENCY_KEY_CONFLICT on the control plane means one key was reused with a different payload. Use a fresh key for a different change, or resend the original payload unchanged.
• SDK_RETRIES_INVALID is thrown at construction when retries is set above 0.