Knap for Dart

A simple, fast, and safe template language for turning data into Markdown using variables, filters, and logic. Inspired by Obsidian Knap.

Features

• Safe Execution: AST-based interpreter with zero eval or arbitrary JavaScript/Dart code execution.
• Markdown-first: Built-in filters for wikilink, list, task_list, table, callout, quote, tag, and escape_md.
• Whitespace Trimming: Liquid/Jinja-compatible {{- -}} and {%- -%} whitespace control.
• Variables & Statements: Property and index access, plus {% set name = expr %}.
• Comments: {# comment #} and {#- comment -#}.
• Rich Logic: if / elif / else branching, for ... in ... else loops with loop variables (loop.index, loop.first, loop.last, loop.revindex, etc.).
• Extended Filters: Date formatting (date, date_modify), case conversion (snake, camel, kebab, pascal), and data manipulation (merge, unique, yaml, hard_break).
• Async Filter Support: Both synchronous (render()) and asynchronous (renderAsync()) evaluation.
• Built-in CLI: dart run knap render <template.md> --data <data.json>.

Getting Started

Add knap to your pubspec.yaml:

dependencies:
  knap: ^2026.9.25

Usage Example

import 'package:knap/knap.dart';

void main() {
  final engine = KnapEngine.standard();

  const template = '''
# {{ title | trim }}

> [!INFO] Summary
> {{ summary }}

## Tags
{{ tags | list }}

## Highlights
{% for h in highlights -%}
- {{ h.text }} ({{ h.note | default: "No note" }})
{% endfor %}

## Related Links
{% for link in links -%}
- {{ link.title | wikilink }}
{% endfor %}
''';

  final markdown = engine.render(template, data: {
    'title': '  Understanding Knap Engine  ',
    'summary': 'A safe, fast template language for Markdown.',
    'tags': ['obsidian', 'markdown', 'dart'],
    'highlights': [
      {'text': 'Zero eval safety', 'note': 'Crucial for apps'},
      {'text': 'Markdown optimized', 'note': null},
    ],
    'links': [
      {'title': 'Obsidian Clipper Docs'},
    ],
  });

  print(markdown);
}

CLI Usage

# Render inline template
dart run knap render --template "Hello {{ name | upper }}!" --data '{"name": "obsidian"}'

# Render template file with JSON data file
dart run knap render template.md --data data.json --output note.md