> For the complete documentation index, see [llms.txt](https://docs.midpointapi.com/midpoint-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.midpointapi.com/midpoint-documentation/core-concepts/midpoints/sources.md).

# Sources

Every midpoint has a Source that initiates a request. Midpoint sources specify exactly how an off-chain workflow begins, and passes any relevant data related to the request to downstream tasks. 

**Startpoint Called**

Startpoint Called is used to trigger a midpoint from on-chain by making a call to the `callMidpoint` function in a Midpoint-deployed contract. Startpoint Called is used when creating oracles, data bridges, or any other workflow that begins with a contract on chain 'initiating' the workflow. For more information about Startpoint Called sources, go to [Startpoint Called](/midpoint-documentation/sources/startpoint-called.md).

```json
{
    "startpointCalledSource": {
        "whitelist": [
            {
                "chainId": "",
                "contractAddress": ""
            }
        ],
        "variables": [
            {
                "name": "",
                "datatype": ""
            }
        ],
        "extracts": [
            {
                "name": "",
                "from": ""
            }
        ],
        "excludeLogs": []
    }
}
```

**EVM Event Emitted**

EVM Event Emitted is used to trigger a midpoint whenever an on-chain event is emitted. These can be any event from a contract currently deployed on-chain, and does not have to go through [Startpoints](/midpoint-documentation/more-reading/startpoints.md). When configuring an EVM Event Emitted source, you can specify indexed parameters, and particular values to listen for, if you want to listen for filtered events. EVM Event Emitted is used when creating alerts, listeners, data bridges, or any other workflow that begins with a contract on chain performing a particular action. For more information about the EVM Event Emitted task, go to [EVM Event Emitted](/midpoint-documentation/sources/evm-event-emitted.md).

```json
{
    "evmEventEmittedSource": {
        "chainId": "",
        "contractAddress": "",
        "eventName": "",
        "arguments": [
            {
                "name": "",
                "datatype": "",
                "indexed": false,
                "value": ""
            }
        ],
        "extracts": [
            {
                "name": "",
                "from": ""
            }
        ],
        "excludeLogs": []
    }
}
```

**Cron Job Triggered**

Cron Job Triggered is used to trigger a midpoint by following a crontab. This can be used to trigger a midpoint at a regular interval, such as every every minute, every thirty minutes, every hour, every week, or every month. Cron Job Triggered is used when creating price feeds, alerts, or any workflow that requires a regular execution of a midpoint. For more information about Cron Job Triggered, go to [Cron Job Triggered](/midpoint-documentation/sources/cron-job-triggered.md).

```json
{
    "cronJobTriggeredSource": {
        "crontab": "",
        "extracts": [
            {
                "name": "",
                "from": ""
            }
        ],
        "excludeLogs": []
    }
}
```

Sources have several common fields with [Tasks](/midpoint-documentation/core-concepts/midpoints/tasks.md). These components are outlined in [Source and Task Definitions](/midpoint-documentation/core-concepts/midpoints/source-and-task-definitions.md).

Don't see a Source that you need for your off-chain workflow? Get in touch.