> ## Documentation Index
> Fetch the complete documentation index at: https://kwala.network/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Event listeners

> Continuously run blockchain event listeners on every supported chain

Kwala runs event listeners continuously on all supported chains. It monitors smart contract events and triggers your workflows the moment a matching event is emitted.

## Basic event trigger

The following example demonstrates a basic event-based trigger that monitors a smart contract on Ethereum mainnet for `Transfer` events. Whenever tokens are transferred from the specified contract, this trigger will activate the workflow.

```yaml theme={null}
trigger:
  triggerChainID: 1
  triggerSourceContract: "0x742d35Cc6e9A5f1e7A0e6FD4C8b2Bc3F5d9E1234"
  triggerSourceContractABI: '[{"anonymous":false,"inputs":[{"indexed":true,"name":"from","type":"address"},{"indexed":true,"name":"to","type":"address"},{"indexed":false,"name":"value","type":"uint256"}],"name":"Transfer","type":"event"}]'
  triggerEventName: "Transfer"
```

## Filtered event trigger

You can add filters to specify which events trigger your workflow. For example, the  following configuration only activates when transfers come from a specific address and exceed 1 token in value:

```yaml theme={null}
trigger:
  triggerChainID: 1
  triggerSourceContract: "0x742d35Cc6e9A5f1e7A0e6FD4C8b2Bc3F5d9E1234"
  triggerSourceContractABI: '[...]'
  triggerEventName: "Transfer"
  triggerEventFilter:
    from: "0xSpecificAddress..."
    value: ">1000000000000000000"  # Greater than 1 token
```

Some common filter operators include:

* Exact match: `"0xAddress..."`
* Greater than: `">value"`
* Less than: `"<value"`
* Range: `">=value,<=value"`
* Multiple values: `["value1", "value2"]`

## Accessing event data

When event listeners subscribe to your event, they can access event data using the `re.event()` syntax:

```yaml theme={null}
APIPayload:
  sender: "re.event(0)"    # First event parameter
  amount: "re.event(1)"    # Second event parameter
```

The index maps to the position of values in the event signature. For example, with `LowPolBalance(address,uint256)`, `re.event(0)` returns the address and `re.event(1)` returns the uint256 value.

## Listening to Kwala Function events

Workflows can also listen to events emitted by [Kwala Functions](/concepts/functions), enabling you to chain workflows together through computed events.

```yaml theme={null}
TriggerEventName: TokenTransferEvaluated(from string, to string, amount number, category string)
RepeatEvery: event
ExecuteAfter: event
```

This allows you to build event-driven pipelines where one function's output triggers another workflow. For example, a function that categorizes transfers can emit events that trigger notifications or further on-chain actions.

For more details, see [Listen to Kwala function events](/concepts/functions#listen-to-kwala-function-events).

## Use cases

The following use cases show event listeners in action as part of theiw workflows:

<CardGroup cols={2}>
  <Card title="Cryptocurrency deposit alerts" icon="bell" href="/use-cases/cryptocurrency-deposit-alerts">
    Get notified when deposits arrive
  </Card>

  <Card title="Low balance notifier" icon="wallet" href="/use-cases/low-wallet-balance-notifier">
    Alert when wallet balance drops
  </Card>
</CardGroup>

## Next steps

<CardGroup cols={2}>
  <Card title="Event-based triggers" icon="bolt" href="/concepts/triggers#event-based-triggers">
    Detailed trigger configuration reference
  </Card>

  <Card title="Address tracking" icon="magnifying-glass" href="/concepts/address-tracking">
    Monitor wallet addresses for activity
  </Card>
</CardGroup>