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Jinja Templating

BAML prompts use Minijinja templates for dynamic content generation. Jinja is a mature templating language popular with Python developers.

tip

Use the BAML VSCode Playground preview to see the fully rendered prompt, including complex logic.

Basic Syntax​

SyntaxPurpose
{% ... %}Execute statements (loops, conditionals)
{{ ... }}Output expressions or variables
{# ... #}Comments (not rendered)

Quick Examples​

Variable Output​

{{ user.name }}
{{ items|length }}

Conditional Statements​

function MyFunc(user: User) -> string {
    prompt #"
        {% if user.is_active %}
            Welcome back, {{ user.name }}!
        {% else %}
            Please activate your account.
        {% endif %}
    "#
}

Loops​

function MyFunc(messages: Message[]) -> string {
    prompt #"
        {% for message in messages %}
            {{ message.user_name }}: {{ message.content }}
        {% endfor %}
    "#
}

Setting Variables​

function MyFunc(items: Item[]) -> string {
    prompt #"
        {% set total_price = 0 %}
        {% for item in items %}
            {% set total_price = total_price + item.price %}
        {% endfor %}
        Total price: {{ total_price }}
    "#
}

Including Templates​

template_string PrintUserInfo(arg1: string, arg2: User) #"
    {{ arg1 }}
    The user's name is: {{ arg2.name }}
"#

function MyFunc(arg1: string, user: User) -> string {
    prompt #"
        Here is the user info:
        {{ PrintUserInfo(arg1, user) }}
    "#
}

Special BAML Variables​

VariableDescription
ctx.output_formatAuto-generated output schema
ctx.clientCurrent client/model info
_.role()Set message role

See Also​