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HCS-12: HashLinks SDK

Build interactive, decentralized experiences on Hedera without smart contracts. HashLinks combines WebAssembly logic, Gutenberg UI blocks, and a composition layer to create powerful applications with minimal fees.

HashLinks enables you to:

  • Execute business logic deterministically through WebAssembly modules
  • Create rich UI components using WordPress Gutenberg blocks
  • Compose applications by binding actions to blocks via assemblies
  • Store everything on-chain using Hedera Consensus Service topics
  • Run anywhere with both server-side and browser-based clients

Quick Start​

Installation​

npm install @hashgraphonline/standards-sdk

Basic Setup​

import { HCS12Client, NetworkType, Logger } from '@hashgraphonline/standards-sdk';

const client = new HCS12Client({
  network: NetworkType.TESTNET,
  mirrorNode: 'https://testnet.mirrornode.hedera.com',
  logger: new Logger({ module: 'HCS12' }),
  hcs12: { operatorId: '0.0.123456', operatorPrivateKey: 'your-private-key' },
});

await client.initializeRegistries();

Browser Setup​

import { HCS12BrowserClient, NetworkType } from '@hashgraphonline/standards-sdk';

const browserClient = new HCS12BrowserClient({
  network: NetworkType.TESTNET,
  mirrorNode: 'https://testnet.mirrornode.hedera.com',
  hwc: hashinalsWalletConnectSDK,
});

API Surface & Modules​

The HCS-12 SDK exports:

  • Clients: HCS12BaseClient, HCS12Client, HCS12BrowserClient
  • Composition & UI: builders (Action/Block/Assembly), rendering
  • Registries & Types: discovery/catalogue helpers, canonical types
  • Validation & WASM: zod schemas, WasmValidator, wasm utilities

See dedicated pages for actions, blocks, assembly, rendering, registries, wasm and security.

Core Architecture​

Actions (WebAssembly Logic)​

interface WasmInterface {
  INFO(): string;
  POST(...): Promise<string>;
  GET(...): Promise<string>;
}

Blocks (UI Components)​

const block = {
  name: 'hashlink/counter',
  template_t_id: '0.0.789',
  attributes: { count: { type: 'number', default: 0 } },
};

Assemblies (Composition Layer)​

const assembly = {
  blocks: [blockId],
  actions: { increment: actionId },
  attributes: { count: 10 },
};