Track pool updates (V1)

Below are the common methods to track updates in liquidity reserve balances:

Polling Sync events for all pools
Polling Sync events for a pool
Subscription using eth_subscribe (coming later - HIP-694)

For production environments, it’s highly recommended to use a paid Mirror Node provider for commercial and high-traffic purposes. While Hedera’s public mirror node offers free REST API and JSON API endpoints, they have global rate limits. These are best suited for development or low rate usage scenarios.

Polling Sync events for all pools

No gas cost — read-only call. Whenever the reserve values for a pool contract are updated, either due to liquidity changes or a swap, a Sync event is emitted from the contract, containing the updated reserve values for the token pair. The following code demonstrates how to listen for Sync events for all pools using REST API or JSON RPC.

Listening to ‘Sync’ events without specifying an address in the filter data will return logs for all pools on SaucerSwap, as well as other DEXs on Hedera that share the same ‘topic0’ hash signature for the ‘Sync’ event. To identify and filter specific pools, extract the pool’s EVM address from the log.

JSON RPC
REST API

Resources:

import * as ethers from 'ethers'; //V6

//Set one of Hedera's JSON RPC Relay as the provider
const provider = new ethers.JsonRpcProvider(hederaJsonRelayUrl, '', {
  batchMaxCount: 1, //workaround for V6
});

//load ABI data containing the Sync event
const abiInterfaces = new ethers.Interface(abi);

const filter = {
  topics: [abiInterfaces.getEvent('Sync')!.topicHash], //topic0 filter
  fromBlock: fromBlock,
  toBlock: toBlock,
};

const logs = await provider.getLogs(filter);
for (const log of logs) {
  const parsedLog = abiInterfaces.parseLog({ topics: log.topics.slice(), data: log.data });
  const {reserve0, reserve1} = parsedLog!.args; //reserve values in smallest unit
  const poolAddress = log.address;
  console.log(`Pool: ${poolAddress}, reserve0: ${reserve0}, reserve1: ${reserve1}`);
}

Resources:

import * as ethers from 'ethers'; //V6

//load ABI data containing the Sync event
const abiInterfaces = new ethers.Interface(abi);

let params = `timestamp=gte:${unixFrom}&timestamp=lte:${unixTo}`;
params += `&topic0=${abiInterfaces.getEvent('Sync')!.topicHash}`;

const url = `${mirrorNodeBaseUrl}/api/v1/contracts/results/logs?${params}`;
const response = await axios.get(url);
const logs = response.data.logs;

for (const log of logs) {
  const {reserve0, reserve1} = abiInterfaces.decodeEventLog('Sync', log.data);
  console.log(`Pair: ${log.address}, reserve0: ${reserve0}, reserve1: ${reserve1}`);
}

Polling Sync events for a pool

JSON RPC
REST API

Resources:

import * as ethers from 'ethers'; //V6

//Set one of Hedera's JSON RPC Relay as the provider
const provider = new ethers.JsonRpcProvider(hederaJsonRelayUrl, '', {
  batchMaxCount: 1, //workaround for V6
});

//load ABI data containing the Sync event
const abiInterfaces = new ethers.Interface(abi);

const filter = {
  topics: [abiInterfaces.getEvent('Sync')!.topicHash], //topic0 filter
  fromBlock: fromBlock,
  toBlock: toBlock,
  address: poolEvmAddress, //pool address starting with 0x
};

const logs = await provider.getLogs(filter);
for (const log of logs) {
  const parsedLog = abiInterfaces.parseLog({ topics: log.topics.slice(), data: log.data });
  const {reserve0, reserve1} = parsedLog!.args; //reserve values in smallest unit
  const poolAddress = log.address;
  console.log(`reserve0: ${reserve0}, reserve1: ${reserve1}`);
}

Resources:

import * as ethers from 'ethers'; //V6

//load ABI data containing the Sync event
const abiInterfaces = new ethers.Interface(abi);

let params = `timestamp=gte:${unixFrom}&timestamp=lte:${unixTo}`;
params += `&topic0=${abiInterfaces.getEvent('Sync')!.topicHash}`;

const url = `${mirrorNodeBaseUrl}/api/v1/contracts/${contractIdEvm}/results/logs?${params}`;
const response = await axios.get(url);
const logs = response.data.logs;

for (const log of logs) {
  const {reserve0, reserve1} = abiInterfaces.decodeEventLog('Sync', log.data);
  console.log(`reserve0: ${reserve0}, reserve1: ${reserve1}`);
}

Getting started

V1 guides

V2 guides

V3 order book

More guides

Security

AI

Track pool updates (V1)

Polling Sync events for all pools

Polling Sync events for a pool

Next steps

Get pool reserves (V1)

Track swap events (V1)

​Polling Sync events for all pools

​Polling Sync events for a pool

​Next steps

Get pool reserves (V1)

Track swap events (V1)

Polling Sync events for all pools

Polling Sync events for a pool

Next steps