Templates

A template is HTML and CSS with a few extras. Values from data are inserted with {{ }}, and {% %} adds logic. The syntax is Tera, close to Jinja and Django templates.

<h1>Invoice {{ number }}</h1>
<p>{{ customer.name }}, issued {{ issued | date(style="long") }}</p>

<table>
  {% for item in items %}
  <tr>
    <td>{{ item.name }}</td>
    <td>{{ item.amount | currency(code="USD") }}</td>
  </tr>
  {% endfor %}
</table>

{% if discount %}
<p>Discount applied</p>
{% endif %}

<p>Total {{ total | currency(code="USD") }}</p>

Values

data is a JSON object. Reach into objects with a dot (customer.name) and loop over arrays with {% for %}. A variable called locale is always available and holds the locale of the render.

Values are HTML-escaped, so a customer name such as <b>Ana</b> appears as text, not as markup. Your template is trusted markup; your data is not.

Logic

• {% if x %}…{% elif y %}…{% else %}…{% endif %} and comparisons such as x > 1.
• {% for item in items %} with loop.index, loop.first and loop.last.
• Arithmetic: {{ price * qty }}.
• {% set name = value %} to name an intermediate value.

Tera’s own filters (upper, lower, round, length and others) work too. The service adds three for formatting; see Locales and formatting.

What templates cannot do

Templates cannot include other files or read anything outside the render. The output of one render is capped by your plan, and a template that produces too much is refused.

Saving templates

Create and edit templates in the portal, which previews and validates as you type, or through the API. A template must compile to be saved.

curl -X POST https://api.example.com/v1/templates \
  -H "Authorization: Bearer $RUSTEDF_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "name": "Invoice", "source": "<h1>{{ number }}</h1>", "locale": "en-US",
        "sample_data": { "number": "2025-0042" } }'

sample_data is only for the portal’s preview. Each change raises the template’s version. Templates belong to one account: another account’s template id is a 404.

Limits on data

data must be a JSON object, at most 32 levels deep and 200,000 values, and no larger than your plan’s input limit.