Route Salesforce leads with round-robin using Flow Builder

Prerequisites

Salesforce org with Flow Builder access (Enterprise, Unlimited, or Developer edition)
System Administrator profile or "Manage Flows" permission
Slack workspace with Salesforce for Slack app installed (for notifications)
A list of Salesforce User IDs for your rep rotation

Overview

Flow Builder has no native round-robin logic. The core pattern is to store a counter in a Custom Setting, increment it on each new Lead, and use modulo arithmetic to pick the next rep. You'll split the work into a before-save flow (fast field update for OwnerId) and an after-save flow (Slack notification, since HTTP callouts aren't allowed in before-save context).

Step 1: Create a Custom Setting for the counter

Go to Setup → Custom Settings → New.

Label: Round Robin Counter
API Name: Round_Robin_Counter__c
Setting Type: Hierarchy
Visibility: Public

Add a custom field:

Field Label: Last Index
API Name: Last_Index__c
Type: Number (0 decimal places)
Default Value: 0

After saving, click Manage and create an org-level default record with Last_Index__c = 0.

Why a Custom Setting?

Custom Settings are accessible in flows without a SOQL query counting against governor limits. They persist across transactions, making them ideal for storing a simple counter.

Step 2: Create a Custom Metadata Type for the rep roster

Go to Setup → Custom Metadata Types → New.

Label: Round Robin Rep
API Name: Round_Robin_Rep__mdt

Add these fields:

Field	API Name	Type
Rep Order	`Rep_Order__c`	Number (0 decimals)
User ID	`User_Id__c`	Text (18 chars)
Slack User ID	`Slack_User_Id__c`	Text (15 chars)
Is Active	`Is_Active__c`	Checkbox (default: true)

Create records for each rep in the rotation:

Label	Rep Order	User ID	Slack User ID	Is Active
Alice Smith	0	005xx0000012345	U01AAAA	true
Bob Jones	1	005xx0000023456	U02BBBB	true
Carol Chen	2	005xx0000034567	U03CCCC	true
Dave Kim	3	005xx0000045678	U04DDDD	true

Skip reps who are out of office

Uncheck Is_Active__c for reps who are unavailable. The flow will skip inactive reps automatically.

Step 3: Create the before-save flow (assignment)

Go to Setup → Flows → New Flow → Record-Triggered Flow.

Object: Lead
Trigger: A record is created
Optimize for: Fast Field Updates (Before Save)

Get the current counter

Add a Get Records element:

Object: Round_Robin_Counter__c
Store: First record → varCounter

Get active reps

Add a Get Records element:

Object: Round_Robin_Rep__mdt
Filter: Is_Active__c equals true
Sort: Rep_Order__c, Ascending
Store: All records → colReps

Calculate assignment with a Formula

Add a Formula resource:

Name: frmNextIndex
Type: Number
Formula: MOD({!varCounter.Last_Index__c}, {!colReps.Size})

This gives you the index of the next rep to assign.

Get the specific rep

Add an Assignment element to loop through the collection and pick the rep at the calculated index, or use a Loop element with a counter variable that breaks when it matches frmNextIndex.

Update the Lead owner

Add an Assignment element:

Set: {!$Record.OwnerId} = the selected rep's User_Id__c

Since this is a before-save flow, the field update happens automatically — no separate Update Records element needed.

Increment the counter

Add an Update Records element:

Object: Round_Robin_Counter__c
Filter: Use the record ID from varCounter
Set: Last_Index__c = {!varCounter.Last_Index__c} + 1

Before-save flows can't make HTTP callouts

You cannot send Slack messages from a before-save flow. The assignment logic must be in a before-save flow for performance (no extra DML), but the Slack notification needs a separate after-save flow or Platform Event.

Step 4: Create the after-save flow (Slack notification)

Create a second Record-Triggered Flow:

Object: Lead
Trigger: A record is created
Optimize for: Actions and Related Records (After Save)
Entry condition: OwnerId is not null

Send Slack notification

If you have Salesforce for Slack installed, add a Send Slack Message action:

Slack Workspace: Select your connected workspace
Channel or User: The assigned rep's Slack User ID (you'll need to look this up from the Custom Metadata Type using the Lead's OwnerId)
Message: Include the lead's Name, Email, Company, and a link back to the Lead record

Alternatively, add an HTTP Callout action (available in Flow Builder as an External Service or Apex invocable):

URL: https://slack.com/api/chat.postMessage
Method: POST
Headers: Authorization: Bearer xoxb-YOUR-BOT-TOKEN
Body: Channel set to the rep's Slack User ID, with lead details in the message text

Step 5: Activate and test

Activate both flows
Create a test Lead manually or via the API
Verify the Lead's OwnerId was set to the expected rep
Check Slack for the notification DM
Create a few more Leads and confirm the rotation cycles through all reps

Single active assignment rule conflict

If your org already has an active Lead Assignment Rule, it will run after your before-save flow. The assignment rule could overwrite the OwnerId your flow just set. Either deactivate the existing rule or add logic to your rule that preserves flow-assigned owners.

Alternative: Queue + Omni-Channel

If you're on Enterprise+ edition, Salesforce Omni-Channel provides workload-based routing out of the box:

Create a Lead Queue and add your reps as members
Set your assignment rule to route all Leads to the queue
Enable Omni-Channel and configure a Routing Configuration with "Least Active" or "Most Available" routing
Reps receive Leads in their Omni-Channel widget based on current workload

This is the officially supported path for workload-balanced routing, but it requires Enterprise edition, Omni-Channel setup, and reps to be logged into the Omni-Channel widget.

Cost

Flow Builder: Included in all Salesforce editions with Flow access (Enterprise+)
Custom Settings and Custom Metadata Types: Included, no additional cost
Omni-Channel: Included in Enterprise and Unlimited editions