Skip to main content

Variables

Variables in BAML prompts allow you to inject dynamic content.

Basic Variable Output​

Use double curly braces to output variable values:

{{ variable_name }}
{{ user.name }}
{{ items[0] }}

Function Parameters​

Function parameters are automatically available as variables:

function Greet(name: string, age: int) -> string {
    client "openai/gpt-4o"
    prompt #"
        Hello {{ name }}, you are {{ age }} years old.
    "#
}

Accessing Object Properties​

Access nested properties using dot notation:

class User {
    name string
    profile Profile
}

class Profile {
    bio string
}

function DescribeUser(user: User) -> string {
    client "openai/gpt-4o"
    prompt #"
        Name: {{ user.name }}
        Bio: {{ user.profile.bio }}
    "#
}

Array Access​

Access array elements by index:

{{ items[0] }}
{{ messages[1].content }}

Setting Variables​

Define local variables using {% set %}:

{% set greeting = "Hello" %}
{{ greeting }}, {{ name }}!

{% set total = 0 %}
{% for item in items %}
    {% set total = total + item.price %}
{% endfor %}
Total: {{ total }}

Default Values​

Provide default values for optional or undefined variables:

{{ user_name|default("Guest") }}
{{ pi or 3.14159 }}

See Also​