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# Logic

Use conditionals, loops, and variable assignment in Web Clipper templates.

Web Clipper supports template logic for conditionals, loops, and variable assignment. This syntax is inspired by Twig and Liquid templating languages.

# Conditionals

Use {% if %} to conditionally include content based on variables or expressions.

{% if author %}
Author: {{author}}
{% endif %}

Use {% else %} to provide fallback content, and {% elseif %} to chain multiple conditions:

{% if status == "published" %}
Live article
{% elseif status == "draft" %}
Draft article
{% else %}
Unknown status
{% endif %}

# Comparison operators

The following comparison operators are supported:

Operator Description
== Equal to
!= Not equal to
> Greater than
< Less than
>= Greater than or equal to
<= Less than or equal to
contains Check if string contains substring, or array contains value

Examples:

  • {% if title == "Home" %} — string equality
  • {% if price >= 100 %} — numeric comparison
  • {% if title contains "Review" %} — substring check
  • {% if tags contains "important" %} — array membership

# Logical operators

Combine conditions using logical operators:

Operator Alternative Description
and && Both conditions must be true
or || At least one condition must be true
not ! Negates a condition

Examples:

  • {% if author and published %} — both must exist
  • {% if draft or archived %} — either condition
  • {% if not hidden %} — negation
  • {% if (premium or featured) and published %} — grouped conditions

# Truthiness

When a variable is used without a comparison operator, it's evaluated for "truthiness":

  • false, null, undefined, empty string "", and 0 are considered falsy.
  • Empty arrays [] are considered falsy.
  • Everything else is truthy.
{% if content %}
Has content
{% endif %}

# Assign a variable

Use {% set %} to create or modify variables within your template:

{% set slug = title|lower|replace:" ":"-" %}
File: {{slug}}.md

Variables can be set to:

  • Other variables: {% set name = author %}
  • Literals: {% set count = 5 %} or {% set label = "Draft" %}
  • Expressions with filters: {% set excerpt = content|truncate:100 %}
  • Selector results: {% set comments = selector:.comment %}

Variables set with {% set %} can be used in subsequent template logic and in {{variable}} output.

# Fallbacks

Use the ?? operator to provide fallback values when a variable is empty or undefined:

{{title ?? "Untitled"}}

If title is empty, undefined, or falsy, the fallback value "Untitled" will be used instead.

This is a shorthand for the equivalent if statement:

{% if title %}{{title}}{% else %}Untitled{% endif %}

# Chaining fallbacks

You can chain multiple fallbacks:

{{title ?? headline ?? "No title"}}

This will use title if available, otherwise headline, otherwise the string "No title".

# With filters

Filters bind more tightly than ??, so filters are applied before the fallback check:

{{title|upper ?? "UNTITLED"}}

This applies upper to title first, then falls back to "UNTITLED" if the result is empty. To apply filters to the fallback value, use parentheses or separate expressions:

{{title ?? "Untitled"|lower}}

This will use title if available, otherwise apply lower to the fallback, resulting in "untitled".

# Loops

Use {% for %} to iterate over arrays:

{% for item in schema:author %}
- {{item.name}}
{% endfor %}

# Loop sources

You can loop over:

  • Schema arrays: {% for item in schema:author %}
  • Selector results: {% for comment in selector:.comment %}
  • Variables set earlier: {% set items = selector:.item %}{% for item in items %}

# Loop variables

Inside a loop, you have access to a loop object with the following properties:

Variable Description
loop.index Current iteration (1-indexed)
loop.index0 Current iteration (0-indexed)
loop.first true if first iteration
loop.last true if last iteration
loop.length Total number of items 
{% for tag in tags %}
{{loop.index}}. {{tag}}
{% if loop.last %} (end of list){% endif %}
{% endfor %}

For backwards compatibility, you can also use item_index (where item is your iterator variable name) to get the 0-indexed position:

{% for tag in tags %}
{{tag_index}}. {{tag}}
{% endfor %}

# Accessing array items by index

Use bracket notation to access array elements by index:

{{items[0]}}
{{items[loop.index0]}}

This is useful when you need to access items from multiple arrays in parallel:

{% set transcripts = selector:.transcript-text %}
{% set timestamps = selector:.timestamp %}

{% for line in transcripts %}
{{timestamps[loop.index0]}} - {{line}}
{% endfor %}

Bracket notation also works with object properties:

{{user["name"]}}
{{data["my-key"]}}

# Nested loops

Loops can be nested for complex data structures:

{% for section in sections %}
## {{section.title}}
{% for item in section.items %}
- {{item}}
{% endfor %}
{% endfor %}

# Combine logic

Conditionals and loops can be combined:

{% for item in items %}
{% if item.active %}
- {{item.name}}
{% endif %}
{% endfor %}

# Evaluation order

Template logic is processed in the following order:

  1. Template logic — {% if %}, {% for %}, {% set %}, and {{variables}} are evaluated first
  2. Prompt variables — Prompt variables like {{"summarize this"|prompt}} are sent to the Interpreter after template logic is complete

This means you can use template logic to construct prompts dynamically, but prompt results are not available for use in conditionals or loops.

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