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Identifying Users

User identification connects events to specific users, enabling retention analysis and user-level insights.

How It Works​

  1. Anonymous ID: SDKs auto-generate a unique ID for each device/browser
  2. Identified ID: When you call identify(), this ID takes precedence
  3. Persistence: Both IDs are persisted across sessions

Basic Usage​

// After user logs in
identify('user_123');

// After user logs out
resetIdentity();

When to Identify​

Call identify() when:

  • User logs in
  • User creates an account
  • User authenticates via OAuth
// After successful login
async function onLoginSuccess(user) {
  identify(user.id);
  track('user_logged_in');
}

When to Reset​

Call resetIdentity() when:

  • User logs out
  • User switches accounts
async function onLogout() {
  track('user_logged_out');
  resetIdentity();
}

Anonymous Users​

Before calling identify(), events are still tracked with an anonymous ID. This allows:

  • Pre-registration funnel analysis
  • Conversion tracking for signups
  • Session-based analysis
// Before login - tracked with anonymous ID
track('page_viewed', { page: 'pricing' });
track('signup_started');

// After signup - tracked with identified ID
identify('new_user_456');
track('signup_completed');

User ID Best Practices​

Do​

  • Use stable, unique IDs (database IDs, UUIDs)
  • Use the same ID across platforms
  • Identify immediately after authentication

Don't​

  • Use PII (email, phone) as user ID
  • Change user IDs after creation
  • Use session or temporary IDs
// Good
identify('usr_abc123');
identify('550e8400-e29b-41d4-a716-446655440000');

// Avoid
identify('john@example.com');  // PII
identify('session_xyz');        // Not stable

Cross-Platform Identity​

Use the same user ID across all platforms:

// iOS
MostlyGoodMetrics.identify(userId: "usr_abc123")
// Android
MostlyGoodMetrics.identify("usr_abc123")
// Web
MostlyGoodMetrics.identify('usr_abc123');

This links all activity to the same user in your analytics.

Session IDs​

In addition to user ID, each app launch generates a unique session ID:

  • Auto-generated on SDK initialization
  • Included with every event
  • Helps analyze within-session behavior

You don't need to manage session IDs - they're handled automatically.