HashLinks - Actions, Blocks, and Assembly Standard

Status: Draft

Authors

• Kantorcodes https://twitter.com/kantorcodes

Abstract

HashLinks provides a framework for building interactive experiences on Hedera without the overhead of smart contracts. The standard combines WebAssembly modules for logic execution, WordPress Gutenberg blocks for UI components, and an assembly layer for composition.

Normative language in this document uses the key words MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY as described in RFC 2119.

Motivation

Hedera's ecosystem needs better composability solutions. While smart contracts offer powerful capabilities, they're often expensive and complex for many use cases. HashLinks addresses this gap by providing:

1. Deterministic logic execution through WebAssembly without smart contract fees
2. Reusable UI components based on proven standards (Gutenberg)
3. On-chain verification without relying on centralized infrastructure
4. Seamless integration with existing Hedera wallets and tools

The standard consists of three interconnected layers:

• Actions - WASM modules for deterministic execution
• Blocks - UI components for user interaction
• Assembly - Composition layer for combining actions and blocks

For implementation details, see the Standards SDK HCS-12 Guide which documents the TypeScript/JavaScript implementation.

Architecture Overview

The HashLinks architecture consists of three core components:

1. Actions: WebAssembly modules that execute business logic
2. Blocks: UI components built on the Gutenberg block standard
3. Assembly: Composition layer that binds actions to blocks

Basic Architecture

The relationship between components:

Detailed Architecture

Complete system architecture including all dependencies:

Topic System

HashLinks leverages HCS-2 for registry management, following the principle of no admin keys to ensure decentralization.

Topic Types

Registry structure and storage locations:

Topic Type	Purpose	Configuration
Action Registry	Stores WASM module references	Non-indexed (latest version)
Assembly Registry	Complete HashLink configurations	Indexed (maintains history)
HashLinks Registry	Global directory of HashLinks	Non-indexed
Block Storage	Block definitions and templates	HCS-1 protocol
Resource References	Asset loading mechanism	HCS-3 protocol

Registries SHOULD support HIP-991 fee collection for sustainability.

Topic Memo Format

Following HCS-2 specification:

hcs-12:{indexed}:{ttl}:{type}:[additional parameters]

Where:

• indexed indicates whether all messages need to be read (0) or only the latest message (1)
• ttl specifies a time-to-live in seconds for caching
• type defines the component type using an enum value
• Additional parameters vary by topic type

Type Enum Values

Type Enum	Component Type	Description
0	Action	WASM module registry (non-indexed, similar to HCS-6)
1	Assembly	Composition registry (indexed)
2	HashLinks	Global directory registry (non-indexed)

Action Registry Topic Memo

hcs-12:1:60:0

Assembly Registry Topic Memo

hcs-12:0:60:1

HashLinks Registry Topic Memo

hcs-12:1:60:2

WebAssembly Interface Stability

HashLinks implementations MUST store both the WASM binary and its JavaScript wrapper on-chain. This ensures consistent execution across different environments:

1. JavaScript Wrapper Requirement - The wasm-bindgen generated JavaScript must be inscribed alongside the WASM
2. Version Tracking - The interface_version field tracks the wasm-bindgen version used
3. Stable Execution - Both files together ensure deterministic execution regardless of client implementation

This approach addresses the inherent instability of WebAssembly imports and the complexity of wasm-bindgen's memory management.

Operation Reference

This section defines all operations available in the HCS-12 protocol. Operations MUST be submitted as JSON messages to the appropriate registry topics.

Action Registry Operations

Operation	Description	Required Fields
register	Register a new WASM action module	p, op, t_id, hash, wasm_hash

Register Action

Registers a new WASM module with its metadata and verification hashes. Messages MUST include the required fields noted above and MAY include optional fields where specified:

{
  "p": "hcs-12",
  "op": "register",
  "t_id": "0.0.123456",
  "hash": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
  "wasm_hash": "a1b2c3d4e5f6789012345678901234567890123456789012345678901234567890",
  "js_t_id": "0.0.123457",
  "js_hash": "5f6e7d8c9b0a1234567890123456789012345678901234567890123456789012",
  "interface_version": "0.2.92",
  "info_t_id": "0.0.123458",
  "validation_rules": {
    "amount": {
      "type": "number",
      "min": 0,
      "max": 1000000
    }
  },
  "m": "Token transfer action v1.0.0"
}

Assembly Registry Operations

Operation	Description	Required Fields
register	Create a new assembly	p, op, name, version
add-action	Add an action to the assembly	p, op, t_id, alias
add-block	Add a block to the assembly	p, op, block_t_id
update	Update assembly metadata	p, op

Register Assembly

Creates a new assembly that can combine actions and blocks:

{
  "p": "hcs-12",
  "op": "register",
  "name": "defi-dashboard",
  "version": "1.0.0",
  "description": "Complete DeFi dashboard with swapping and staking",
  "tags": ["defi", "trading", "staking"],
  "author": "0.0.123456"
}

Add Action

Adds a WASM action to the assembly:

{
  "p": "hcs-12",
  "op": "add-action",
  "t_id": "0.0.123456",
  "alias": "swap",
  "config": {
    "slippage": 0.5,
    "deadline": 300
  }
}

Add Block

Adds a UI block to the assembly:

{
  "p": "hcs-12",
  "op": "add-block",
  "block_t_id": "0.0.234568",
  "actions": {
    "swap": "0.0.123456",
    "approve": "0.0.123457"
  },
  "attributes": {
    "title": "Quick Swap",
    "defaultToken": "HBAR"
  }
}

Update Assembly

Updates assembly metadata:

{
  "p": "hcs-12",
  "op": "update",
  "description": "Updated DeFi dashboard with new features",
  "tags": ["defi", "trading", "staking", "lending"]
}

HashLinks Registry Operations

Operation	Description	Required Fields
register	Register a HashLink in the global directory	p, op, t_id, name

Register HashLink

Registers an assembly in the global HashLinks directory:

{
  "p": "hcs-12",
  "op": "register",
  "t_id": "0.0.567890",
  "name": "Ultimate DeFi Dashboard",
  "description": "All-in-one DeFi management interface",
  "tags": ["defi", "featured"],
  "category": "finance",
  "author": "0.0.123456",
  "website": "https://example.com"
}

Security Considerations

Key security requirements:

1. Hash Verification: Clients MUST verify WASM, JavaScript wrapper, and metadata hashes before execution.
2. Template Security: Templates MUST NOT include inline scripts; all resources MUST be loaded via HCS-3.
3. State Isolation: Blocks MUST be isolated by default, with explicit permission required for communication.
4. Action Validation: All actions MUST be registered with parameter validation and HTML sanitization.
5. Interface Verification: The JavaScript wrapper MUST match the WASM module interface version.

Implementation Guide

Step 1: Create Your WASM Action

Step 2: Create UI Block

Step 3: Create Assembly

Step 4: Register in Global Directory

Step 5: User Interaction Flow

Client Architecture

Required components for HashLinks client implementation:

HCS-10 Interoperability

HashLinks interoperate with the HCS-10 OpenConvAI standard for agent-to-agent and human–agent interactions.

Agent Integration

Agents can embed HashLinks in their communications to provide interactive experiences:

{
  "p": "hcs-10",
  "op": "message",
  "operator_id": "0.0.789101@0.0.123456",
  "data": "{\"content\":\"Here's a visualization of the data you requested\",\"hashlink\":\"hcs://15/0.0.567890\"}",
  "m": "Message with embedded HashLink"
}

Example: DeFi loan coordination between agents:

Human–Agent Interaction

HashLinks enable agents to provide interactive interfaces rather than text-based instructions:

Integration Architecture

Technical Implementation

1. Message Extension: Add a hashlink field to HCS-10 messages for HashLink references
2. Context Passing: WASM modules receive conversation context via the memo parameter

Compatibility

This standard is compatible with:

• HCS-1 for file storage
• HCS-2 for topic registries
• HCS-3 for resource loading
• HCS-11 for agent profiles
• WordPress Gutenberg block editor

References

1. HCS-1 Standard: File Data Management
2. HCS-2 Standard: Advanced Topic Registries
3. HCS-3 Standard: Recursion within Hedera Consensus Service
4. WordPress Gutenberg Block API