# hedera-consensus-service

A skill that teaches your agent Hedera Consensus Service in JavaScript: create topics, submit messages, subscribe to the stream via mirror node.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 547 installs · ★ 28
- Author: hedera-dev
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/hedera-dev/hedera-skills/tree/HEAD/plugins/native-services-js/skills/hedera-consensus-service/SKILL.md
- Updated: 2026-09-03
- HTML: https://affpapa.org/en/nevibecode/skills/hedera-consensus-service

## What it does

The skill treats HCS as an ordered message log with consensus timestamps. It ships ready patterns on `@hiero-ledger/sdk`: creating a topic, submitting a message, subscribing to the stream, custom per-message fees, and chunking large payloads.

Two setup paths are covered — `Client.forName` with `setOperator`, and `Wallet` with `LocalProvider`. The signer route uses `freezeWithSigner`, `signWithSigner`, `executeWithSigner` and `getReceiptWithSigner`. Key behaviour is spelled out too: no `adminKey` means the topic can't be updated or deleted, and no `submitKey` means anyone can post.

One thing that bites people: after creating a topic, wait a few seconds before subscribing, because the mirror node needs time to sync it. Messages over 1024 bytes get split into chunks on submit and reassembled on subscribe. You'll need `OPERATOR_ID` and `OPERATOR_KEY` in your environment.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add hedera-dev/hedera-skills --skill hedera-consensus-service -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/hedera-consensus-service/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/hedera-consensus-service/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add hedera-dev/hedera-skills --skill hedera-consensus-service -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/hedera-consensus-service/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add hedera-dev/hedera-skills --skill hedera-consensus-service -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/hedera-consensus-service/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install hedera-dev/hedera-skills hedera-consensus-service
```

2. **Manually: put the files in place**
- File: `.github/skills/hedera-consensus-service/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add hedera-dev/hedera-skills --skill hedera-consensus-service -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/hedera-dev/hedera-skills --path plugins/native-services-js/skills/hedera-consensus-service
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/hedera-consensus-service/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add hedera-dev/hedera-skills --skill hedera-consensus-service -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/hedera-dev/hedera-skills/tree/HEAD/plugins/native-services-js/skills/hedera-consensus-service/SKILL.md

## When to use it
- create an HCS topic with admin and submit keys
- submit a message and read back its sequence number
- subscribe to a live message stream through a mirror node
- set a fixed per-message fee and a payer limit
- send a payload larger than 1024 bytes in chunks

## Example prompts
- create a Hedera topic with memo "event log" and adminKey from OPERATOR_KEY
- submit "Hello, Hedera!" to the topic and print topicSequenceNumber
- subscribe to the topic with setStartTime(0) and log each consensusTimestamp

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: c67703d85a9a8ee7.

BEGIN THIRD-PARTY FILE c67703d85a9a8ee7
````text
---
name: hedera-consensus-service
description: "How to create topics, submit messages, and subscribe to real-time message streams on Hedera using the Hiero JavaScript SDK (@hiero-ledger/sdk). Use this skill whenever the user wants to work with Hedera Consensus Service (HCS), including topic creation, message submission, pub/sub messaging, mirror node subscriptions, chunked large messages, topic fees, or any consensus-related operation in JavaScript or TypeScript. Also trigger when users mention @hashgraph/sdk topic operations, event logging on Hedera, decentralized messaging, audit trails, or ordered message streams."
---

# Hedera Consensus Service (HCS) — JavaScript SDK

HCS provides a decentralized, ordered message log with consensus timestamps. It works like a pub/sub system: you create **topics**, **submit messages** to them, and **subscribe** to receive messages in real time via mirror nodes. Messages are immutable, ordered, and timestamped by network consensus — useful for audit trails, event logs, supply chain tracking, and decentralized communication.

## Setup

All imports come from `@hiero-ledger/sdk`. Two setup patterns:

### Client + setOperator (direct)
```js
import { Client, AccountId, PrivateKey } from "@hiero-ledger/sdk";

const client = Client.forName(process.env.HEDERA_NETWORK)
    .setOperator(
        AccountId.fromString(process.env.OPERATOR_ID),
        PrivateKey.fromStringECDSA(process.env.OPERATOR_KEY),
    );
```

### Wallet + LocalProvider (signer-based)
```js
import { Wallet, LocalProvider } from "@hiero-ledger/sdk";

const provider = new LocalProvider();
const wallet = new Wallet(process.env.OPERATOR_ID, process.env.OPERATOR_KEY, provider);
```

With the signer pattern, use `freezeWithSigner(wallet)`, `signWithSigner(wallet)`, `executeWithSigner(wallet)`, and `getReceiptWithSigner(wallet)`.

## Creating a Topic

```js
import { TopicCreateTransaction } from "@hiero-ledger/sdk";

const { topicId } = await (
    await new TopicCreateTransaction()
        .setTopicMemo("My event log")
        .setAdminKey(operatorKey)       // allows update/delete
        .setSubmitKey(operatorKey)      // restricts who can post
        .execute(client)
).getReceipt(client);

console.log(`Topic created: ${topicId.toString()}`);
```

**Key behaviors**:
- Without an `adminKey`, the topic cannot be updated or deleted (only expiration can be extended).
- Without a `submitKey`, anyone can submit messages.
- Default auto-renew period is 90 days.

### Topic with Custom Fees
````
END THIRD-PARTY FILE c67703d85a9a8ee7

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