Splitting audiences into distinct groups

it is not recommended to retrieve the MCID (ECID) directly from the cookie for a Target Profile Script.

If you try to read the AMCV cookie using user.cookie() inside a profile script, you will run into race conditions. Target executes profile scripts on the Adobe Edge cluster before the browser cookie state is updated or synchronized, meaning the cookie might be missing or stale on the first hit of a session.

Instead, you should leverage Target's native Request Tokens or pass it explicitly via your implementation layer. Here are the two best practice methods to handle this securely.

Method 1: The Native Request Token Pattern (Recommended)

Adobe Target automatically extracts the Marketing Cloud ID from the incoming request payload (whether via at.js 2.x or the Web SDK) and stores it in a system variable called user.marketingCloudVisitorId.

You can access this natively in a Profile Script without parsing any cookies:

JavaScript

// Profile Script Name: profile.ecid_bucket
var ecid = user.marketingCloudVisitorId;

if (!ecid) {
    // Fallback to a random number if ECID isn't resolved yet
    return Math.floor(Math.random() * 10); 
}

// Extract the last digit of the ECID string to create 10 disjoint groups (0-9)
var lastDigit = ecid.substr(ecid.length - 1);

// If the last character is a letter (hex), parse it to an int, or just grab a modulo
return isNaN(lastDigit) ? (ecid.charCodeAt(ecid.length - 1) % 10) : parseInt(lastDigit);

• Why this works: It bypasses the browser cookie entirely. It reads the ID directly from the payload that the Adobe Identity Service already attached to the network request.

Method 2: The Data Layer / Web SDK Parameter Pattern

If you want absolute control over the split logic before the request even reaches Target, handle the hashing in your tag manager (Adobe Launch/Tags) and pass it as a custom profile parameter.

1. In Adobe Tags: Create a Data Element that reads the ECID from the Identity Core extension, hashes it into a bucket (e.g., bucket_3), and maps it to a Target parameter.

2. In the Target Call: Pass it as profile.ecid_bucket = bucket_3.

3. In Target Audiences: You can now create your disjoint audiences instantly in the UI by targeting Profile Attribute -> ecid_bucket -> equals -> bucket_3.