---
schema_version: "1"
id: f9a7958c1ad0f00a6bc682c7783834d738dff62bce256e0f14402023c86380aa
title: Check External Systems to Determine Availability of Service Resources
collection: admin
version: current
locale: en-us
portal_url: https://docs.salesforce.com/admin/current/en-us/platform/264-0-0/ls_read_external_events_overview.md
canonical_url: https://help.salesforce.com/s/articleView?id=platform.ls_read_external_events_overview.htm&release=264.0.0&type=5
source_site: help.salesforce.com
content_type: documentation
content_hash: 9152085dbc244bc8cbf67fbb74f26d441c75b0c4ad3f2f0e5b87cfaaa2d4e125
description: Use the provided LxScheduler.ServiceResourceScheduleHandler Apex interface to write an Apex class that checks external systems, such as external calendar events, to find time slots where service resources are already booked. Then associate this Apex class with Salesforce Scheduler flows or API calls through the Check External Systems for Resource Availability scheduling policy rule.
products:
  - Scheduler
  - Salesforce Platform
release: "264"
---
# Check External Systems to Determine Availability of Service Resources

Use the provided LxScheduler.ServiceResourceScheduleHandler Apex interface to write an Apex class that checks external systems, such as external calendar events, to find time slots where service resources are already booked. Then associate this Apex class with Salesforce Scheduler flows or API calls through the Check External Systems for Resource Availability scheduling policy rule.

### Required Editions

<table class="slds-table slds-table_bordered slds-max-medium-table_stacked slds-m-bottom_small edition"><colgroup><col></colgroup><tbody><tr class=""><td class="slds-cell-wrap" style="vertical-align:top;">Available in: Lightning Experience.</td></tr><tr class=""><td class="slds-cell-wrap" style="vertical-align:top;">Available in: <strong>Enterprise</strong> and <strong>Unlimited</strong> Editions</td></tr></tbody></table>

- **[Check External Calendars to Determine Resource Availability](https://help.salesforce.com/s/articleView?id=platform.ls_read_external_calendar.htm&release=264.0.0&type=5)**  
    When you run a Salesforce Scheduler flow or make an API call, the Apex interface makes a synchronous call to the Apex class. The Apex interface passes the details of the requested service resources and timelines for which Salesforce Scheduler wants to find the resources’ availability on the external calendar. The Apex class checks the external calendar events and returns the time slots where resources aren’t available. Salesforce Scheduler excludes the unavailable time slots during appointment scheduling.
- **[Apex Interface Implementation Limitations and Error Codes](https://help.salesforce.com/s/articleView?id=platform.ls_ext_cal_integration_troubleshooting.htm&release=264.0.0&type=5)**  
    When determining the availability of service resources, limitations apply when you use a custom Apex class to check external calendar events.