Learn how to create a new topic and submit your first message on Hedera testnet using the JavaScript, Java, or Go SDK. A topic on the Hedera Consensus Service (HCS) is like a public channel: anyone who knows the topic ID can publish timestamped messages, and anyone can subscribe to the stream from a mirror node.
Prerequisites
A Hedera testnet operator account ID and DER-encoded private key (from the Quickstart ).
A small amount of testnet HBAR (ℏ) to cover the fees
Note
You can always check the " ✅ Code Check " section at the bottom of each page to view the entire code if you run into issues. You can also post your issue to the respective SDK channel in our Discord community here .
Install the SDK
Open your terminal and create a directory hedera-examples
directory. Then change into the newly created directory:
Copy mkdir hedera-examples && cd hedera-examples
Initialize a node.js
project in this new directory:
Ensure you have Node.js v18
or later installed on your machine. Then, install the JavaScript SDK .
Copy npm install --save @hashgraph/sdk
Update your package.json
file to enable ES6 modules and configure the project:
Copy {
"name" : "hedera-examples" ,
"version" : "1.0.0" ,
"type" : "module" ,
"main" : "createTopicDemo.js" ,
"scripts" : {
"start" : "node createTopicDemo.js"
} ,
"keywords" : [] ,
"author" : "" ,
"license" : "ISC" ,
"dependencies" : {
"@hashgraph/sdk" : "^2.69.0"
}
}
Create a createTopicDemo.js
file and add the following imports:
Copy import {
Client,
TopicCreateTransaction,
TopicMessageSubmitTransaction
} from "@hashgraph/sdk";
Add the Java SDK depenency to your Maven project's pom.xml
and create your source file:
Create a new Maven project and name it HederaExamples
. Add the following dependencies to your pom.xml
file:
Copy <dependencies>
<dependency>
<groupId>com.hedera.hashgraph</groupId>
<artifactId>sdk</artifactId>
<version>2.61.0</version>
</dependency>
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.10.1</version>
</dependency>
<dependency>
<groupId>io.grpc</groupId>
<artifactId>grpc-netty-shaded</artifactId>
<version>1.73.0</version>
</dependency>
</dependencies>
Or for Gradle projects using the Groovy DSL, add these dependencies to your build.gradle
file and install the dependencies using ./gradlew build
Copy plugins {
id 'java'
id 'application'
}
repositories {
mavenCentral()
}
dependencies {
implementation 'com.hedera.hashgraph:sdk:2.60.0'
implementation 'com.google.code.gson:gson:2.10.1'
implementation 'io.grpc:grpc-netty-shaded:1.61.0'
}
application {
mainClass = 'CreateTopicDemo'
// or 'com.example.CreateTopicDemo' if it's in a package
}
Create a CreateTopicDemo.java
class in src/main/java/
with the following imports:
Copy import com.hedera.hashgraph.sdk.*;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.URI;
import com.google.gson.Gson;
import com.google.gson.JsonObject;
import com.google.gson.JsonArray;
public class CreateTopicDemo {
public static void main(String[] args) throws Exception {
// Your topic creation code will go here
}
}
Create a new file create_topic_demo.go
and import the following packages to your file:
Copy import (
"encoding/base64"
"encoding/json"
"fmt"
"io"
"net/http"
"os"
"time"
hedera "github.com/hiero-ledger/hiero-sdk-go/v2/sdk"
)
In your project's root directory, initialize modules and pull in the Go SDK :
Copy go mod init create_topic_demo
go get github.com/hiero-ledger/hiero-sdk-go/v2@latest
go mod tidy
Environment Variables
Set your operator credentials as environment variables. Your OPERATOR_ID
is your testnet account ID. Your OPERATOR_KEY
is your testnet account's corresponding ECDSA private key.
Copy export OPERATOR_ID="0.0.1234"
export OPERATOR_KEY="3030020100300506032b657004220420..."
Step 1: Initialize Hedera Client
Load your operator credentials from environment variables and configure your Hedera testnet client. The client manages your connection to the Hedera test network and uses your operator account to sign transactions and pay transaction fees.
Copy // Load your operator credentials
const operatorId = process.env.OPERATOR_ID;
const operatorKey = process.env.OPERATOR_KEY;
// Initialize your testnet client and set operator
const client = Client.forTestnet()
.setOperator(operatorId, operatorKey);
Copy // Load your operator credentials
AccountId operatorId = AccountId.fromString(System.getenv("OPERATOR_ID"));
PrivateKey operatorKey = PrivateKey.fromString(System.getenv("OPERATOR_KEY"));
// Initialize your testnet client and set operator
Client client = Client.forTestnet().setOperator(operatorId, operatorKey);
Copy // Load your operator credentials
operatorId, _ := hedera.AccountIDFromString(os.Getenv("OPERATOR_ID"))
operatorKey, _ := hedera.PrivateKeyFromString(os.Getenv("OPERATOR_KEY"))
// Initialize the client for testnet
client := hedera.ClientForTestnet()
client.SetOperator(operatorId, operatorKey)
Step 2: Create a new topic
TopicCreateTransaction
builds and sends the transaction to register a new HCS topic with the provided memo, and once it reaches consensus you retrieve the transaction receipt to extract the new topicId
.
Why messages?
Messages on HCS are consensus-timestamped and immutable. Once published, they become part of the permanent record that anyone can verify and subscribe to in real-time.
Copy // Build and send the transaction
const txResponse = await new TopicCreateTransaction()
.setTopicMemo("My first HCS topic") // optional description
.execute(client);
const receipt = await txResponse.getReceipt(client);
const topicId = receipt.topicId;
console.log(`\nTopic created: ${topicId.toString()}`);
Copy // Build and send the create‐topic transaction
TransactionResponse txResponse = new TopicCreateTransaction()
.setTopicMemo("My first HCS topic") // optional description
.execute(client);
// Fetch the receipt to get the new topic ID
TransactionReceipt receipt = txResponse.getReceipt(client);
TopicId topicId = receipt.topicId;
System.out.println("Topic created: " + topicId);
Copy // build & execute the topic creation transaction
transaction := hedera.NewTopicCreateTransaction().
SetTopicMemo("My first HCS topic")
txResponse, err := transaction.Execute(client)
if err != nil {
panic(err)
}
receipt, err := txResponse.GetReceipt(client)
if err != nil {
panic(err)
}
topicID := *receipt.TopicID
fmt.Println("\nTopic created:", topicID.String())
What just happened?
The SDK built a TopicCreateTransaction .
Your operator key signed and paid the fee.
Hedera nodes reached consensus and returned a unique topic ID (shard.realm.num
).
Step 3: Submit Message to Topic
TopicMessageSubmitTransaction
constructs and sends a transaction that submits your payload (string, bytes, or Uint8Array
) as a message to a specified HCS topic. Once it reaches consensus, the message becomes part of that topic’s immutable record.
Copy // Build & execute the message submission transaction
const message = "Hello, Hedera!";
const messageTransaction = new TopicMessageSubmitTransaction()
.setTopicId(topicId)
.setMessage(message);
await messageTransaction.execute(client);
console.log(`\nMessage submitted: ${message}\n`);
Copy // build & execute the message submission transaction
String message = "Hello, Hedera!";
TopicMessageSubmitTransaction messageTransaction = new TopicMessageSubmitTransaction()
.setTopicId(topicId)
.setMessage(message);
messageTransaction.execute(client);
System.out.println("\nMessage submitted: " + message);
Copy // build & execute the message submission transaction
message := "Hello, Hedera!"
messageTransaction := hedera.NewTopicMessageSubmitTransaction().
SetTopicID(topicID).
SetMessage([]byte(message))
_, err = messageTransaction.Execute(client)
if err != nil {
panic(err)
}
fmt.Printf("\nMessage submitted: %s\n", message)
Note
Messages can be up to 1 KiB each. Larger payloads must be chunked automatically by the SDK or split manually
Step 4: Query Messages Using Mirror Node API
Use the Mirror Node REST API to verify your message was published to the topic. Mirror nodes provide free access to network data without transaction fees. Mirror nodes stream every consensus-timestamped message in order, letting your app react in real time.
API endpoint:
Copy /api/v1/topics/{topicId}/messages
Replace the placeholder:
{topicId} - Your topic ID from the creation transaction
Why this endpoint?
This endpoint retrieves all messages published to a specific topic, ordered by consensus timestamp. It returns detailed information including message content, timestamp, and sequence number, making it ideal for verifying your message was published successfully.
Example URLs:
Copy const mirrorNodeUrl = `https://testnet.mirrornode.hedera.com/api/v1/topics/${topicId}/messages`;
Copy String mirrorNodeUrl = "https://testnet.mirrornode.hedera.com/api/v1/topics/" + topicId + "/messages";
Copy mirrorNodeUrl := "https://testnet.mirrornode.hedera.com/api/v1/topics/" + topicID.String() + "/messages"
Complete Implementation:
Copy // wait for Mirror Node to populate data
console.log("\nWaiting for Mirror Node to update...");
await new Promise((resolve) => setTimeout(resolve, 6000));
// query messages using Mirror Node
const mirrorNodeUrl = `https://testnet.mirrornode.hedera.com/api/v1/topics/${topicId}/messages`;
const response = await fetch(mirrorNodeUrl);
const data = await response.json();
if (data.messages && data.messages.length > 0) {
const latestMessage = data.messages[data.messages.length - 1];
const messageContent = Buffer.from(latestMessage.message, "base64")
.toString("utf8")
.trim();
console.log(`\nLatest message: ${messageContent}\n`);
} else {
console.log("No messages found yet in Mirror Node");
}
client.close();
Copy // wait for Mirror Node to populate data
System.out.println("\nWaiting for Mirror Node to update...");
Thread.sleep(6000);
// query messages using Mirror Node
String mirrorNodeUrl = "https://testnet.mirrornode.hedera.com/api/v1/topics/" + topicId + "/messages";
HttpClient httpClient = HttpClient.newHttpClient( );
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(mirrorNodeUrl))
.build();
HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString( ));
Gson gson = new Gson();
JsonObject data = gson.fromJson(response.body(), JsonObject.class);
if (data.has("messages") && data.getAsJsonArray("messages").size() > 0) {
JsonArray messages = data.getAsJsonArray("messages");
JsonObject latestMessage = messages.get(messages.size() - 1).getAsJsonObject();
String encodedMessage = latestMessage.get("message").getAsString();
String messageContent = new String(java.util.Base64.getDecoder().decode(encodedMessage)).trim();
System.out.println("\nLatest message: " + messageContent + "\n");
} else {
System.out.println("No messages found yet in Mirror Node");
}
client.close();
Copy // wait for Mirror Node to populate data
fmt.Println("Waiting for Mirror Node to update...")
time.Sleep(6 * time.Second)
// query messages using Mirror Node
mirrorNodeUrl := "https://testnet.mirrornode.hedera.com/api/v1/topics/" + topicID.String() + "/messages"
resp, err := http.Get(mirrorNodeUrl)
if err != nil {
panic(err)
}
defer resp.Body.Close()
body, err := io.ReadAll(resp.Body)
if err != nil {
panic(err)
}
var data struct {
Messages []struct {
Message string `json:"message"`
} `json:"messages"`
}
err = json.Unmarshal(body, &data)
if err != nil {
panic(err)
}
if len(data.Messages) > 0 {
latestMessage := data.Messages[len(data.Messages)-1]
decodedMessage, _ := base64.StdEncoding.DecodeString(latestMessage.Message)
fmt.Println("\nLatest message:", strings.TrimSpace(string(decodedMessage)))
} else {
fmt.Println("No messages found yet in Mirror Node")
}
client.Close()
✅ Code check
Before running your project, verify your code matches the complete example:
JavaScript
Copy import {
Client,
TopicCreateTransaction,
TopicMessageSubmitTransaction,
} from "@hashgraph/sdk";
async function createTopicDemo() {
// load your operator credentials
const operatorId = process.env.OPERATOR_ID;
const operatorKey = process.env.OPERATOR_KEY;
// initialize the client for testnet
const client = Client.forTestnet().setOperator(operatorId, operatorKey);
// build & execute the topic creation transaction
const transaction = new TopicCreateTransaction().setTopicMemo(
"My first HCS topic"
);
const txResponse = await transaction.execute(client);
const receipt = await txResponse.getReceipt(client);
const topicId = receipt.topicId;
console.log(`\nTopic created: ${topicId}`);
// build & execute the message submission transaction
const message = "Hello, Hedera!";
const messageTransaction = new TopicMessageSubmitTransaction()
.setTopicId(topicId)
.setMessage(message);
await messageTransaction.execute(client);
console.log(`\nMessage submitted: ${message}`);
// wait for Mirror Node to populate data
console.log("\nWaiting for Mirror Node to update...");
await new Promise((resolve) => setTimeout(resolve, 6000));
// query messages using Mirror Node
const mirrorNodeUrl = `https://testnet.mirrornode.hedera.com/api/v1/topics/${topicId}/messages`;
const response = await fetch(mirrorNodeUrl);
const data = await response.json();
if (data.messages && data.messages.length > 0) {
const latestMessage = data.messages[data.messages.length - 1];
const messageContent = Buffer.from(latestMessage.message, "base64")
.toString("utf8")
.trim();
console.log(`\nLatest message: ${messageContent}\n`);
} else {
console.log("No messages found yet in Mirror Node");
}
client.close();
}
createTopicDemo().catch(console.error);
Java
Copy import com.hedera.hashgraph.sdk.*;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.net.URI;
import com.google.gson.Gson;
import com.google.gson.JsonObject;
import com.google.gson.JsonArray;
public class CreateTopicDemo {
public static void main(String[] args ) throws Exception {
// load your operator credentials
String operatorId = System.getenv("OPERATOR_ID");
String operatorKey = System.getenv("OPERATOR_KEY");
// initialize the client for testnet
Client client = Client.forTestnet()
.setOperator(AccountId.fromString(operatorId), PrivateKey.fromString(operatorKey));
// build & execute the topic creation transaction
TopicCreateTransaction transaction = new TopicCreateTransaction()
.setTopicMemo("My first HCS topic");
TransactionResponse txResponse = transaction.execute(client);
TransactionReceipt receipt = txResponse.getReceipt(client);
TopicId topicId = receipt.topicId;
System.out.println("\nTopic created: " + topicId);
// build & execute the message submission transaction
String message = "Hello, Hedera!";
TopicMessageSubmitTransaction messageTransaction = new TopicMessageSubmitTransaction()
.setTopicId(topicId)
.setMessage(message);
messageTransaction.execute(client);
System.out.println("\nMessage submitted: " + message);
// wait for Mirror Node to populate data
System.out.println("\nWaiting for Mirror Node to update...");
Thread.sleep(6000);
// query messages using Mirror Node
String mirrorNodeUrl = "https://testnet.mirrornode.hedera.com/api/v1/topics/" + topicId + "/messages";
HttpClient httpClient = HttpClient.newHttpClient( );
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create(mirrorNodeUrl))
.build();
HttpResponse<String> response = httpClient.send(request, HttpResponse.BodyHandlers.ofString( ));
Gson gson = new Gson();
JsonObject data = gson.fromJson(response.body(), JsonObject.class);
if (data.has("messages") && data.getAsJsonArray("messages").size() > 0) {
JsonArray messages = data.getAsJsonArray("messages");
JsonObject latestMessage = messages.get(messages.size() - 1).getAsJsonObject();
String encodedMessage = latestMessage.get("message").getAsString();
String messageContent = new String(java.util.Base64.getDecoder().decode(encodedMessage)).trim();
System.out.println("\nLatest message: " + messageContent + "\n");
} else {
System.out.println("No messages found yet in Mirror Node");
}
client.close();
}
}
Go
Copy package main
import (
"encoding/base64"
"encoding/json"
"fmt"
"io"
"net/http"
"os"
"strings"
"time"
hedera "github.com/hiero-ledger/hiero-sdk-go/v2/sdk"
)
func main() {
// load your operator credentials
operatorId, _ := hedera.AccountIDFromString(os.Getenv("OPERATOR_ID"))
operatorKey, _ := hedera.PrivateKeyFromString(os.Getenv("OPERATOR_KEY"))
// initialize the client for testnet
client := hedera.ClientForTestnet()
client.SetOperator(operatorId, operatorKey)
// build & execute the topic creation transaction
transaction := hedera.NewTopicCreateTransaction().
SetTopicMemo("My first HCS topic")
txResponse, err := transaction.Execute(client)
if err != nil {
panic(err)
}
receipt, err := txResponse.GetReceipt(client)
if err != nil {
panic(err)
}
topicID := *receipt.TopicID
fmt.Println("\nTopic created:", topicID.String())
// build & execute the message submission transaction
message := "Hello, Hedera!"
messageTransaction := hedera.NewTopicMessageSubmitTransaction().
SetTopicID(topicID).
SetMessage([]byte(message))
_, err = messageTransaction.Execute(client)
if err != nil {
panic(err)
}
fmt.Printf("\nMessage submitted: %s\n", message)
// Wait for Mirror Node to populate data
fmt.Println("\nWaiting for Mirror Node to update...")
time.Sleep(6 * time.Second)
// query messages using Mirror Node
mirrorNodeUrl := "https://testnet.mirrornode.hedera.com/api/v1/topics/" + topicID.String() + "/messages"
resp, err := http.Get(mirrorNodeUrl)
if err != nil {
panic(err)
}
defer resp.Body.Close()
body, err := io.ReadAll(resp.Body)
if err != nil {
panic(err)
}
var data struct {
Messages []struct {
Message string `json:"message"`
} `json:"messages"`
}
err = json.Unmarshal(body, &data)
if err != nil {
panic(err)
}
if len(data.Messages) > 0 {
latestMessage := data.Messages[len(data.Messages)-1]
decodedMessage, _ := base64.StdEncoding.DecodeString(latestMessage.Message)
fmt.Println("\nLatest message:", strings.TrimSpace(string(decodedMessage)))
} else {
fmt.Println("No messages found yet in Mirror Node")
}
client.Close()
}
Run Your Project
Ensure your environment variables are set:
Copy export OPERATOR_ID="0.0.1234"
export OPERATOR_KEY="3030020100300506032b657004220420..."
Copy node createTopicDemo.js
Copy mvn compile exec:java -Dexec.mainClass="com.example.CreateTopicDemo"
Copy go run create_topic_demo.go
Expected sample output:
Copy Topic created: 0.0.1234567
Message submitted: Hello, Hedera!
Waiting for Mirror Node to update...
Latest message: Hello, Hedera!
‼️ Troubleshooting
Common ERROR messages and solutions ⬇️ Error message
Likely cause
Fix
INSUFFICIENT_PAYER_BALANCE
Not enough HBAR for topic creation fee
Top up your operator account on the testnet faucet
Operator key doesn't match operator account
Verify OPERATOR_KEY matches your OPERATOR_ID
Malformed account ID in environment variables
Verify OPERATOR_ID format is 0.0.1234
Malformed private key in environment variables
Verify OPERATOR_KEY is a valid DER-encoded private key string
Topic ID not found or malformed
Ensure topic was created successfully and ID is correct
Wait a few more seconds and try again - this is normal
What Just Happened?
The SDK built a TopicCreateTransaction
and signed it with your operator key.
A consensus node validated the signature and charged the topic creation fee.
After network consensus, a unique topic ID was assigned and returned in the receipt.
Your message was submitted to the topic and became part of the immutable record.
The Mirror Node API confirmed your message was published with consensus timestamp
Next steps
Subscribe to the topic from your backend or front-end to process messages as they come in
Encrypt messages if you need privacy before publishing
🎉 Great work ! You have created a new topic and broadcasted your first message on Hedera testnet. Keep building!
Additional Resources
Last updated 9 minutes ago