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# Template Interpolation Agent, Say Node & Menu Node
### Template Interpolation
Text fields (Say, Agent, Menu prompts) use {{expression}} interpolation:
Syntax
Purpose
Example
{{expression}}
Variable lookup or expression
Hello {{name}}, you have {{items.length}} items
* {{expression}} — evaluated by the Expression Engine, matches the next }}
* Simple variable names like {{name}} resolve to a variable lookup
* Complex expressions like {{items.filter(x => x.active).length}} are fully evaluated
* The double-brace delimiter avoids collision with JSON content in system prompts
* Non-printable results (objects, arrays) are JSON-stringified; null/undefined produce empty\
string
* Errors preserve the original text and log a warning
### What Template Interpolation Means in an Agent Node, Say Node and Menu Node
* Configure an **Agent Node**
* Inside the **System Prompt** field, you typed:\
`Testing {{`
* As soon as `{{` is typed, a **template helper dropdown** appears
* The dropdown lists:
* **Variables** (`var boolean`, `var number`, `var userEndpoint`, etc.)
* **Slots from Test (agent node)** (example tooltip: *Variable – boolean*)
* **Built‑in functions** (`fn $addDays`, `fn $format`, `fn $now`, etc.)
* **JS native objects/functions** (`Date`, `Math`, `parseInt`, `String`, etc.)
This confirms that **the System Prompt supports template interpolation using `{{ }}` syntax**, with access to typed variables and runtime helpers.
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