---

name: fullstory-anonymize-users version: v3 description: Core concepts for Fullstory's User Anonymization API. Platform-agnostic guide covering session management, privacy compliance, and best practices for logout handling and user switching. See SKILL-WEB.md and SKILL-MOBILE.md for implementation examples. platforms:

• web
• ios
• android
• flutter
• react-native related_skills:
• fullstory-identify-users
• fullstory-user-consent
• fullstory-capture-control
• fullstory-async-methods implementation_files:
• SKILL-WEB.md
• SKILL-MOBILE.md

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Fullstory Anonymize Users API

Implementation Files: This document covers core concepts. For code examples, see:

• SKILL-WEB.md — JavaScript/TypeScript (Browser)
• SKILL-MOBILE.md — iOS, Android, Flutter, React Native

Overview

Fullstory's Anonymize Users API allows developers to release the identity of the current user and create a new anonymous session. This is essential for:

• User Logout: Properly ending an identified session when a user logs out
• Account Switching: Allowing users to switch between accounts cleanly
• Privacy Compliance: Implementing "forget me" or privacy-conscious features
• Shared Devices: Ensuring one user's session doesn't bleed into another's

When you anonymize a user, the current session ends and a fresh anonymous session begins. The previously identified user remains in Fullstory's records, but subsequent activity is no longer linked to them.

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Core Concepts

What Happens When You Anonymize

1. Current session is closed and marked as belonging to the identified user
2. New device identifier is generated — breaking the link to all previous sessions
3. New anonymous session begins with a new session ID
4. Previous user data is preserved — anonymizing doesn't delete history
5. Subsequent activity is anonymous until a new identify call

Cookie/Device Behavior: Normally, the device identifier links all sessions from the same device together. When anonymize is called, Fullstory generates a new identifier, effectively creating a "new device" from Fullstory's perspective. Any future identify calls will only merge sessions from the new identifier, not the old one.

Session Lifecycle

┌─────────────┐  Login   ┌─────────────┐  Logout  ┌─────────────┐
│  Anonymous  │ ───────► │ Identified  │ ───────► │ New Anon    │
│  Session A  │          │  Session B  │          │  Session C  │
└─────────────┘          └─────────────┘          └─────────────┘
                              │
                 identify     │    anonymize
                (uid: 'xxx')  │    

When to Anonymize

Scenario	Should Anonymize?	Reason
User logs out	✅ Yes	Prevents session attribution to wrong user
User switches accounts	✅ Yes	Clean slate before new identification
User requests data deletion	❓ Consider	Part of broader privacy implementation
User clears app data	❌ No	Fullstory handles this automatically
Screen/page navigation	❌ No	Identity persists across screens
Session timeout	❓ Depends	Based on your security requirements

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API Methods by Platform

Platform	Anonymize Method
Web	FS('setIdentity', { anonymous: true })
iOS	FS.anonymize()
Android	FS.anonymize()
Flutter	FS.anonymize()
React Native	FullStory.anonymize()

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Rate Limits

Type	Limit
Sustained	30 calls per page/screen per minute
Burst	10 calls per second

Note: A single call per logout is sufficient. Multiple calls provide no benefit and waste quota.

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Best Practices

1. Track Events BEFORE Anonymizing

Always track important events (like logout) before calling anonymize, so they're attributed to the identified user:

1. Track "User Logged Out" event (attributed to user)
2. Call anonymize
3. Redirect to login screen

2. Anonymize BEFORE Navigation

Always anonymize before navigating away from the current screen, otherwise the call may not complete:

✅ Good: anonymize → navigate
❌ Bad:  navigate → anonymize (may not execute)

3. Single Call Per Logout

One anonymize call is sufficient. Multiple calls:

• Waste API quota
• Create unnecessary session splits
• May hit rate limits

4. Handle All Logout Paths

Audit your application for all ways a user can sign out:

• Manual logout button
• Session timeout
• Account deletion
• Force logout (admin action)
• Token expiration

5. Account Switching Flow

For apps that support multiple accounts:

1. Track "Account Switch" event (current user)
2. Anonymize current session
3. Set up new account context
4. Identify as new user

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Common Patterns

Logout Service Pattern

Create a centralized logout service that:

1. Tracks the logout event
2. Calls backend logout API
3. Clears client-side auth state
4. Anonymizes Fullstory session
5. Navigates to login

Multi-Tenant/Workspace Switching

For apps with workspace or tenant switching:

1. Track workspace switch event
2. Anonymize to end current context
3. Load new workspace context
4. Re-identify user with new workspace properties

Shared Device/Kiosk Mode

For shared devices:

1. Identify user when session starts
2. Set automatic session timeout
3. Anonymize when timeout expires
4. Return to welcome screen

Incognito/Privacy Mode

For privacy-conscious users who want to browse without tracking:

1. Store original user ID
2. Anonymize to stop attribution
3. Show incognito indicator
4. Re-identify when mode is disabled

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Troubleshooting

Session Not Properly Ending

Symptom: New user activity appears under old user

Cause	Solution
Anonymize called after navigation starts	Use async version and await completion
Anonymize never called	Audit all logout paths
Wrong syntax (web)	Use { anonymous: true } not { uid: null }

Too Many Session Splits

Symptom: User has many short, fragmented sessions

Cause	Solution
Calling anonymize on every screen load	Only anonymize on actual logout
Calling anonymize on errors	Only anonymize for identity changes
Multiple anonymize calls in single flow	Use single call per logout

Identity Not Clearing

Symptom: User properties persist after anonymize

Cause	Solution
Re-identifying immediately after anonymize	Wait for new identify call
Cached user data in app	Clear app-level user state

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Key Takeaways for Agent

When helping developers implement User Anonymization:

1. Always emphasize:

   • Anonymize BEFORE navigation/redirects
   • Use the correct platform-specific syntax
   • Track important events BEFORE anonymizing
   • Single call per logout is sufficient
   • Anonymization doesn't delete data, it ends attribution

2. Common mistakes to watch for:

   • Forgetting to anonymize on logout
   • Anonymizing after redirect/navigation starts
   • Using wrong syntax (web: uid: null, uid: 'anonymous')
   • Over-calling anonymize
   • Missing trackEvent before anonymize

3. Questions to ask developers:

   • What are all the logout/signout paths in your app?
   • Do users switch between accounts?
   • Is this a shared device scenario?
   • What events should be tracked before logout?

4. Platform routing:

   • Web (JavaScript/TypeScript) → See SKILL-WEB.md
   • iOS (Swift/SwiftUI) → See SKILL-MOBILE.md § iOS
   • Android (Kotlin) → See SKILL-MOBILE.md § Android
   • Flutter (Dart) → See SKILL-MOBILE.md § Flutter
   • React Native → See SKILL-MOBILE.md § React Native

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Reference Links

• Browser API: https://developer.fullstory.com/browser/identification/anonymize-users/
• iOS API: https://developer.fullstory.com/mobile/ios/identification/anonymize-users/
• Android API: https://developer.fullstory.com/mobile/android/identification/anonymize-users/
• Flutter API: https://developer.fullstory.com/mobile/flutter/identification/anonymize-users/
• React Native API: https://developer.fullstory.com/mobile/react-native/identification/anonymize-users/
• Help Center: https://help.fullstory.com/hc/en-us/articles/360020623514-Anonymizing-Users