Random draws

zend.random draws a value with Sui’s built-in randomness in Zend’s zend::draws contract, and records it once per interaction and label. Both players’ pages can call it; the second call gets the same result.

const { value: [side], transactionId } = await zend.random({
  interactionId: game.id, label: "flip", kind: "int", n: 2,
});

const deal = await zend.random({ interactionId: game.id, label: "deal-1", kind: "shuffle", n: 52 });

const winners = await zend.random({ interactionId: game.id, label: "winners", kind: "pick", n: 300, k: 3 });

Kinds

`kind`	Returns	Range
`int`	One number in `0..n-1`	`n ≥ 2`. A coin flip is `n: 2`
`shuffle`	An order of `0..n-1`	`2 ≤ n ≤ 64`
`pick`	`k` different numbers from `0..n-1`	`1 ≤ k ≤ 64`, `k ≤ n ≤ 1000`

Rules

Each (interaction, label) is drawn once, ever. You can’t redraw "flip" until you like the answer.
Asking again with the same label and the same settings returns the recorded result. Asking with different settings fails with DRAW_MISMATCH.
Labels are 1–25 characters of a-z, 0-9, _ and -.
Up to 50 draws per interaction (TOO_MANY_DRAWS).
Everyone in the interaction’s live room also gets the result as a message from "zend" with data: { type: "random", result }.
Draws cost the user nothing. Each one counts against your app’s network budget.

Result

{
  interactionId: string;
  label: string;
  kind: "int" | "shuffle" | "pick";
  n: number;
  k: number;
  value: number[];
  transactionId: string;              // look it up on Sui
  attestation: AttestReceipt | null;  // Zend's signed record
  verify: { package: string; registry: string };
}

From your server

curl -X POST https://api.usezend.app/api/zend/v2/apps/server/random \
  -H "Authorization: Bearer $ZEND_APP_KEY" \
  -H "Content-Type: application/json" \
  -d '{"interaction_id":"int_...","label":"winners","kind":"pick","n":300,"k":3}'

Your server also receives a random.drawn webhook for every draw, from a page or from your server.

Show that a result was checked

Set check: true on a result card’s slots:

await zend.postCard({
  interactionId: game.id, template: "result", placement: "chat", idempotencyKey: `${game.id}:result`,
  slots: { title: "Heads! Tunde wins", check: true },
});

Zend shows Result checked ✓ under the card only when its own check passes: every record for the interaction is intact and signed by Zend, and each draw matches its record. Interactions without a draw get no badge. Tapping the badge explains what was checked.

Check a draw yourself

On Sui: look up transactionId and find the Drawn event from the package in verify.package.
Offline: check attestation against Zend’s public key with verifyAttestation.

Get started

Build a ZApp

Money

Fair results

Ship

Examples

Kinds

Rules

Result

From your server

Show that a result was checked

Check a draw yourself

​Kinds

​Rules

​Result

​From your server

​Show that a result was checked

​Check a draw yourself

Kinds

Rules

Result

From your server

Show that a result was checked

Check a draw yourself