---
title: Track dynamic variables - Flutter
description: Learn how to track and analyze variable metrics over time in your Flutter app using the CSQ SDK
lastUpdated: 05 January 2026
source_url:
  html: https://docs.contentsquare.com/en/csq-sdk-flutter/experience-analytics/track-dynamic-variables/
  md: https://docs.contentsquare.com/en/csq-sdk-flutter/experience-analytics/track-dynamic-variables/index.md
---

## Usage

Dynamic variables are additional information on the session that can be used to segment sessions.

For example, they can include information on the A/B Test variations displayed to the current user.

## Limits

### On the server side

* It is possible to save up to 40 distinct dynamic variable keys per screen view. If more are received, only the first 40 keys will be kept.
* If you are using the same key twice, the last value associated with the key will be collected.

### On the SDK side

* Every dynamic variable is composed of a pair of key (max. 50 characters) and value (max. 255 characters string or number of type Long between 0 and 232 - 1). In case these maximums length are reached, the SDK will automatically trim the exceeding characters.
* If key or value are empty, the SDK will instead send the literal string "cs-empty".

## Defining dynamic variables

To define and send a dynamic variable, you just need to use the following API.

```dart
import 'package:contentsquare/csq.dart';


final userTypeVar = DynamicVar.fromString(key: 'accountType', value: 'Premium');
CSQ().addDynamicVar(userTypeVar);


final friendCountVar = DynamicVar.fromInt(key: 'numberOfFriends', value: 15);
CSQ().addDynamicVar(friendCountVar);
```

* For `int`, you will be able to do some algebra. Example: sessions with dynamic variable key = "numberOfFriends" and value >= 10
* For `String`, auto-completion and Regular Expression will be available. Example: sessions with dynamic variable key = "accountType" and value is "Premium"

## Sending a dynamic variable for each session

You may want to send a dynamic variable for each session (like the user's country or store). While **triggering the dynamic variable at app launch will cover most cases, it will not be enough**. A session can start when the app is put in foreground, after staying in background for more than 30 minutes. See [Session definition](../data-collection/#session-definition) section for more information.

That is why we also recommend **sending such dynamic variable every time the app enters foreground**.

You can use [`didChangeAppLifecycleState` method ↗](https://api.flutter.dev/flutter/widgets/WidgetsBindingObserver/didChangeAppLifecycleState.html) to detect foreground and trigger a dynamic variable.