Restrict Who Can Hold It

Limit transfers of your stablecoin to accounts your KYC program has approved, using B20 transfer policies.

Keep your stablecoin within a known set of holders with an allowlist: transfers only settle between accounts your KYC program has approved. You manage the list in the Policy Registry and bind it to the token’s transfer scopes.

Demo

New to B20? See the B20 Token Standard for the concepts and a full launch walkthrough. These samples target base-std@v1.0.0, viem@2.55.11, and Base Foundry v1.1.1.

Create and bind a holder allowlist

TypeScript

import { parseEventLogs, type Address } from "viem";
import { account, publicClient } from "../../shared/clients.js";
import { POLICY_REGISTRY, b20Abi, policyRegistryAbi, scope } from "../abi.js";
import { sendContract } from "../write.js";

export async function createHolderAllowlist(token: Address, holders: Address[]) {
  const receipt = await sendContract({
    address: POLICY_REGISTRY,
    abi: policyRegistryAbi,
    functionName: "createPolicyWithAccounts",
    args: [account.address, 1, holders],
  });
  const [created] = parseEventLogs({ abi: policyRegistryAbi, logs: receipt.logs, eventName: "PolicyCreated" });
  const policyId = created.args.policyId;
  for (const policyScope of [scope("TRANSFER_SENDER_POLICY"), scope("TRANSFER_RECEIVER_POLICY")]) {
    await sendContract({ address: token, abi: b20Abi, functionName: "updatePolicy", args: [policyScope, policyId] });
  }
  const saved = await publicClient.readContract({ address: token, abi: b20Abi, functionName: "policyId", args: [scope("TRANSFER_RECEIVER_POLICY")] });
  if (saved !== policyId) throw new Error("Policy was not bound");
  return policyId;
}

See the complete verified B20 examples for imports, client construction, and runnable projects.

The token returns the new policy ID for both transfer policy scopes.

An allowlist denies every account not in the policy. Seed intended holders before binding it, and retain the PolicyCreated ID.

See also

• Block an account
• Policy integration in the B20 standard