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A variable is a named, typed piece of state that lives inside a flow. Variables let a flow remember things: which plan a user tapped, how far they are through a quiz, whether a switch is on. You can show a variable in text, branch on it with dynamic values, change it with actions, and read values your app passes in through the SDK. Variables hold state only. They never directly control a property. To make a property react to a variable, you use a dynamic value.

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Variable types

Every variable has one of four types:
TypeHoldsExample
String (Text)Text"monthly", a name, an email
NumberA number0, 42, a score
Boolean (True/False)true or falsea toggle, a “has agreed” flag
List (Array)A homogeneous list of itemsselected options
A List variable also has a List Item Type (Text Items, Number Items, or Boolean Items). Every item in the list must be that type. A list of text cannot also hold numbers.

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Where a variable’s value comes from

When you create a variable you pick a Variable Type (this is separate from the data type above). It decides where the value comes from and whether the flow can change it.
Variable TypeSourceEditable in the flow?Use it for
Flow StateA constant initial value you set in the editorYes, actions can change itchoices, counters, toggles, anything the flow itself updates
App ParameterA value read from the SDK context at runtimeNo, it is read-onlyuser id, plan, app version, anything the host app knows
  • Flow State is mutable. Its starting value is the Initial Value you type in the dialog. Actions like Set Variable can change it while the flow runs.
  • App Parameter is read-only. The SDK supplies its value from the context your app passes in (see Variables and SDK context). The editor derives the lookup path from the variable name (lowercased, with spaces replaced by underscores), so a name like user.id becomes a nested path lookup. If the app does not provide a value, the Default Value is used as a fallback.
Variables are session-scoped. Their values last for one run of the flow and reset the next time the flow is presented.
You do not set “writable” or “lifecycle” by hand. The editor sets them for you: Flow State is writable, App Parameter is read-only, and both are session state.

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Create a variable

1

Open the Variables tab

In the left sidebar, click Variables. The panel lists every variable in the flow with its type and current value.
2

Click Add

Click Add (top right of the panel) to open the Create Variable dialog.
3

Name it and pick a type

Enter a Name (for example selected_plan) and choose a Type. For a List, also choose a List Item Type.
4

Choose Flow State or App Parameter

Set Variable Type to Flow State (a value the flow owns and changes) or App Parameter (a value the app provides through the SDK).
5

Set the starting value

For Flow State, set the Initial Value. For App Parameter, set a Default Value to fall back to when the app does not provide one.
6

Create

Click Create Variable. The variable appears in the list and is ready to use. To change it later, hover the row and click the edit icon.

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Keys vs names

When you create a variable from this dialog, the editor stores your typed name as the variable’s label and assigns it a generated key like var_ab12cd. The key is what {{ }} interpolation and conditions actually use. You rarely type keys by hand:
  • Text fields have a {} Insert variable button that lists variables by name and splices the correct {{key}} token at your cursor.
  • The condition builder and the Set Variable action both pick variables from a dropdown that shows names, not raw keys.
Variables created by blocks (for example a choice block’s selected_* variable) use readable keys instead of generated ones.

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Using variables

There are four ways to use a variable:
  1. Interpolate it in text. Anywhere text accepts it, {{key}} is replaced with the variable’s current value. For example, a heading of Welcome back, {{first_name}} renders the value of first_name. Use the {} button to insert the right token.
  2. Drive a dynamic value. Feed a variable into a condition to switch a property’s value. See Dynamic values.
  3. Change it with an action. The Set Variable action applies a typed operation (set, increment, toggle, add to list, and so on). Only Flow State variables appear in its picker, because App Parameters are read-only.
  4. Bind it to a component input. A component prop or a custom component input can read from a variable instead of a fixed value.

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Example

A simple plan picker:
  1. Create a Flow State String variable named selected_plan with an Initial Value of monthly.
  2. On a “Monthly” button, add a Set Variable action: selected_plan -> Set to value -> monthly. On a “Yearly” button, set it to yearly.
  3. On a “Continue” button, make the label dynamic: when selected_plan equals yearly, show Continue with Yearly, otherwise Continue. See Dynamic values.
  4. Create an App Parameter String variable named user.id. Use {{user.id}} in a Trigger Event property, or read it on the SDK side for analytics. Your app supplies its value through the SDK context.
The schema for selected_plan looks like this: 
{
  "key": "selected_plan",
  "label": "selected_plan",
  "type": "string",
  "scope": "global",
  "lifecycle": "session",
  "source": { "kind": "constant", "value": "monthly" },
  "writable": true
}

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Common mistakes

  • Wrong type. Storing a number as a String breaks numeric comparisons (greater than, less than) because those operators only work on Number variables. Pick the type that matches how you will use the value.
  • Referencing a key that does not exist. A missing or misspelled variable in {{ }} resolves to an empty string, so the text just disappears. Insert variables with the {} button to avoid typos, and remember that a manually created variable’s key is var_..., not the name you typed.
  • Expecting an App Parameter to change mid-flow. App Parameters are read each time the flow starts. They do not update on their own while a flow is on screen. The app must supply fresh context (see Variables and SDK context).
  • Trying to Set Variable on an App Parameter. Read-only variables do not appear in the Set Variable picker, and a write to one is ignored at runtime.

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Troubleshooting

SymptomLikely causeFix
{{ }} renders nothingThe key does not exist or is misspelledInsert the variable with the {} button; check the key in the Variables panel
A number comparison never matchesThe variable is a String, not a NumberRecreate or edit it as a Number
An App Parameter is always its defaultThe app did not send that key, or the path does not matchConfirm the path matches the SDK context your app sends (iOS)
A Set Variable action does nothingThe target is read-only (an App Parameter)Use a Flow State variable instead