Expressions

Expressions let you compute values directly inside your templates. Instead of calculating totals or formatting data before sending it to the API, you can do it right in the template using simple functions and operators.

Arithmetic operators

You can use standard math operators inside any {{ }} variable block:

Operator	Example	Result
`+`	`{{price + tax}}`	Addition
`-`	`{{total - discount}}`	Subtraction
`*`	`{{items.qty * items.price}}`	Multiplication
`/`	`{{amount / 2}}`	Division

For example, to show the line total in an invoice table row:


{{items.qty * items.unit_price}}

This multiplies quantity by unit price for each row automatically.

Built-in functions

Row-level functions

These functions work on individual values. When used with array fields (like items.qty), they repeat automatically for each row.

Function	Syntax	What it does
`mul`	`{{mul(a, b)}}`	Multiply two values
`add`	`{{add(a, b, c)}}`	Add multiple values
`sub`	`{{sub(a, b)}}`	Subtract b from a
`div`	`{{div(a, b)}}`	Divide a by b

Example — calculate a line total with a discount:


{{sub(mul(items.qty, items.unit_price), items.discount)}}

Aggregate functions

These functions operate on an entire array and return a single value. They do not trigger row repetition.

Function	Syntax	What it does
`sum`	`{{sum(items.amount)}}`	Sum all values of a field
`sumproduct`	`{{sumproduct(items.qty, items.price)}}`	Multiply two fields row by row, then sum the results
`count`	`{{count(items)}}`	Number of items in a list
`avg`	`{{avg(items.price)}}`	Average of a field
`min`	`{{min(items.price)}}`	Smallest value
`max`	`{{max(items.price)}}`	Largest value

Example — show the invoice total:


{{sum(items.amount)}}

Sumproduct

sumproduct multiplies two fields row by row, then sums the results — just like SUMPRODUCT in a spreadsheet.


{{sumproduct(items.qty, items.price)}}

For each item, this computes qty × price, then sums all the line totals. This is typically how you compute an invoice subtotal when your data only contains quantity and unit price.

Filters

Filters transform a value after it has been computed. Use the | symbol to apply a filter.

Formatting numbers

Filter	Example	Output
`round(n)`	`{{total \| round(2)}}`	`19.57`
`int`	`{{value \| int}}`	`42`
`float`	`{{value \| float}}`	`3.14`
`abs`	`{{value \| abs}}`	`5` (from -5)

You can chain filters:


{{items.qty * items.unit_price | round(2)}}

Formatting text

Filter	Example	Output
`upper`	`{{name \| upper}}`	`JOHN DOE`
`lower`	`{{name \| lower}}`	`john doe`
`capitalize`	`{{name \| capitalize}}`	`John doe`
`title`	`{{name \| title}}`	`John Doe`

Working with lists

Filter	Example	What it does
`length`	`{{items \| length}}`	Number of items
`first`	`{{items \| first}}`	First item
`last`	`{{items \| last}}`	Last item
`join(", ")`	`{{tags \| join(", ")}}`	Join items into a string
`sort`	`{{items \| sort}}`	Sort items
`reverse`	`{{items \| reverse}}`	Reverse order

Conditionals

You can show or hide content based on conditions:


{% if payment_status == "paid" %}
  Paid ✓
{% else %}
  Payment pending
{% endif %}

You can also use elif for multiple conditions:


{% if total > 1000 %}
  Premium order
{% elif total > 500 %}
  Standard order
{% else %}
  Small order
{% endif %}

Available comparison operators: ==, !=, <, >, <=, >=

Logical operators: and, or, not

Practical examples

Invoice subtotal, tax, and total


Subtotal: {{sumproduct(items.qty, items.unit_price) | round(2)}}
Tax (10%): {{sumproduct(items.qty, items.unit_price) * 0.1 | round(2)}}
Total: {{sumproduct(items.qty, items.unit_price) * 1.1 | round(2)}}

Item count


{{count(items)}} items in this order

Conditional message


{% if count(items) > 10 %}
  Bulk order — thank you!
{% endif %}

Good to know

Missing variables render as empty — no error is shown in the generated PDF.
Division by zero returns empty instead of crashing.
Floating-point rounding is handled automatically (e.g. 48.18000000000001 becomes 48.18).
Aggregate functions (sum, avg, min, max, count) never trigger row repetition. Row-level functions (mul, add, sub, div) do when referencing array fields.

Next steps

Data Binding — How to define variables and pass data to your templates
Tables — Dynamic tables that grow with your data
System Variables — Built-in variables for dates and page numbers