Custom Filters Reference

SwissArmyHammer includes a comprehensive set of custom Liquid filters designed specifically for prompt engineering and content processing.

Code Filters

format_lang

Formats code with language-specific syntax highlighting hints.

{{ code | format_lang: "rust" }}
{{ code | format_lang: language_var }}

Arguments:

language - Programming language identifier (e.g., “rust”, “python”, “javascript”)

Example:

<!-- Input -->
{{ "fn main() { println!(\"Hello\"); }" | format_lang: "rust" }}

<!-- Output -->
```rust
fn main() { println!("Hello"); }


### extract_functions

Extracts function signatures and definitions from code.

```liquid
{{ code | extract_functions }}
{{ code | extract_functions: "detailed" }}

Arguments:

mode (optional) - “signatures” (default) or “detailed” for full function bodies

Example:

<!-- Input -->
{{ rust_code | extract_functions }}

<!-- Output -->
- fn main()
- fn calculate(x: i32, y: i32) -> i32
- fn process_data(data: &Vec<String>) -> Result<(), Error>

basename

Extracts the filename from a file path.

{{ path | basename }}

Example:

<!-- Input -->
{{ "/usr/local/bin/swissarmyhammer" | basename }}

<!-- Output -->
swissarmyhammer

dirname

Extracts the directory path from a file path.

{{ path | dirname }}

Example:

<!-- Input -->
{{ "/usr/local/bin/swissarmyhammer" | dirname }}

<!-- Output -->
/usr/local/bin

count_lines

Counts the number of lines in text.

{{ text | count_lines }}

Example:

<!-- Input -->
{{ "line 1\nline 2\nline 3" | count_lines }}

<!-- Output -->
3

dedent

Removes common leading whitespace from all lines.

{{ code | dedent }}

Example:

<!-- Input -->
{{ "    fn main() {\n        println!(\"Hello\");\n    }" | dedent }}

<!-- Output -->
fn main() {
    println!("Hello");
}

Text Processing Filters

extract_urls

Extracts all URLs from text.

{{ text | extract_urls }}
{{ text | extract_urls: "list" }}

Arguments:

format (optional) - “array” (default) or “list” for bullet point list

Example:

<!-- Input -->
{{ "Visit https://example.com and https://github.com" | extract_urls }}

<!-- Output -->
["https://example.com", "https://github.com"]

<!-- With list format -->
{{ "Visit https://example.com and https://github.com" | extract_urls: "list" }}

<!-- Output -->
- https://example.com
- https://github.com

slugify

Converts text to a URL-friendly slug.

{{ title | slugify }}

Example:

<!-- Input -->
{{ "Advanced Code Review Helper!" | slugify }}

<!-- Output -->
advanced-code-review-helper

word_wrap

Wraps text at specified column width.

{{ text | word_wrap: 80 }}
{{ text | word_wrap: width_var }}

Arguments:

width - Column width for wrapping (default: 80)

Example:

<!-- Input -->
{{ "This is a very long line that should be wrapped at a specific column width to ensure readability." | word_wrap: 30 }}

<!-- Output -->
This is a very long line that
should be wrapped at a specific
column width to ensure
readability.

indent

Indents all lines by specified number of spaces.

{{ text | indent: 4 }}
{{ text | indent: spaces_var }}

Arguments:

spaces - Number of spaces to indent (default: 2)

Example:

<!-- Input -->
{{ "line 1\nline 2" | indent: 4 }}

<!-- Output -->
    line 1
    line 2

bullet_list

Converts an array to a bullet point list.

{{ array | bullet_list }}
{{ array | bullet_list: "*" }}

Arguments:

bullet (optional) - Bullet character (default: “-”)

Example:

<!-- Input -->
{{ ["Item 1", "Item 2", "Item 3"] | bullet_list }}

<!-- Output -->
- Item 1
- Item 2
- Item 3

<!-- With custom bullet -->
{{ ["Item 1", "Item 2"] | bullet_list: "*" }}

<!-- Output -->
* Item 1
* Item 2

highlight

Highlights specific terms in text.

{{ text | highlight: "keyword" }}
{{ text | highlight: term_var }}

Arguments:

term - Term to highlight

Example:

<!-- Input -->
{{ "This is important text with keywords" | highlight: "important" }}

<!-- Output -->
This is **important** text with keywords

Data Transformation Filters

from_json

Parses JSON string into object/array.

{{ json_string | from_json }}

Example:

<!-- Input -->
{% assign data = '{"name": "John", "age": 30}' | from_json %}
Name: {{ data.name }}
Age: {{ data.age }}

<!-- Output -->
Name: John
Age: 30

to_json

Converts object/array to JSON string.

{{ data | to_json }}
{{ data | to_json: "pretty" }}

Arguments:

format (optional) - “compact” (default) or “pretty” for formatted output

Example:

<!-- Input -->
{% assign user = { "name": "John", "age": 30 } %}
{{ user | to_json: "pretty" }}

<!-- Output -->
{
  "name": "John",
  "age": 30
}

from_csv

Parses CSV string into array of objects.

{{ csv_string | from_csv }}
{{ csv_string | from_csv: ";" }}

Arguments:

delimiter (optional) - Field delimiter (default: “,”)

Example:

<!-- Input -->
{% assign data = "name,age\nJohn,30\nJane,25" | from_csv %}
{% for row in data %}
- {{ row.name }} is {{ row.age }} years old
{% endfor %}

<!-- Output -->
- John is 30 years old
- Jane is 25 years old

to_csv

Converts array of objects to CSV string.

{{ array | to_csv }}
{{ array | to_csv: ";" }}

Arguments:

delimiter (optional) - Field delimiter (default: “,”)

Example:

<!-- Input -->
{% assign users = [{"name": "John", "age": 30}, {"name": "Jane", "age": 25}] %}
{{ users | to_csv }}

<!-- Output -->
name,age
John,30
Jane,25

from_yaml

Parses YAML string into object/array.

{{ yaml_string | from_yaml }}

Example:

<!-- Input -->
{% assign config = "database:\n  host: localhost\n  port: 5432" | from_yaml %}
Host: {{ config.database.host }}
Port: {{ config.database.port }}

<!-- Output -->
Host: localhost
Port: 5432

to_yaml

Converts object/array to YAML string.

{{ data | to_yaml }}

Example:

<!-- Input -->
{% assign config = {"database": {"host": "localhost", "port": 5432}} %}
{{ config | to_yaml }}

<!-- Output -->
database:
  host: localhost
  port: 5432

Hash Filters

md5

Generates MD5 hash of input text.

{{ text | md5 }}

Example:

<!-- Input -->
{{ "hello world" | md5 }}

<!-- Output -->
5d41402abc4b2a76b9719d911017c592

sha1

Generates SHA1 hash of input text.

{{ text | sha1 }}

Example:

<!-- Input -->
{{ "hello world" | sha1 }}

<!-- Output -->
2aae6c35c94fcfb415dbe95f408b9ce91ee846ed

sha256

Generates SHA256 hash of input text.

{{ text | sha256 }}

Example:

<!-- Input -->
{{ "hello world" | sha256 }}

<!-- Output -->
b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9

Utility Filters

ordinal

Converts number to ordinal format (1st, 2nd, 3rd, etc.).

{{ number | ordinal }}

Example:

<!-- Input -->
{{ 1 | ordinal }} item
{{ 22 | ordinal }} place
{{ 103 | ordinal }} attempt

<!-- Output -->
1st item
22nd place
103rd attempt

lorem_words

Generates lorem ipsum text with specified number of words.

{{ count | lorem_words }}

Arguments:

count - Number of words to generate

Example:

<!-- Input -->
{{ 10 | lorem_words }}

<!-- Output -->
Lorem ipsum dolor sit amet consectetur adipiscing elit sed do eiusmod

format_date

Advanced date formatting with custom format strings.

{{ date | format_date: "%Y-%m-%d %H:%M:%S" }}
{{ "now" | format_date: "%B %d, %Y" }}

Arguments:

format - Date format string (uses strftime format)

Common format codes:

%Y - 4-digit year (2024)
%m - Month as number (01-12)
%d - Day of month (01-31)
%H - Hour (00-23)
%M - Minute (00-59)
%S - Second (00-59)
%B - Full month name (January)
%b - Abbreviated month (Jan)
%A - Full weekday name (Monday)
%a - Abbreviated weekday (Mon)

Example:

<!-- Input -->
{{ "2024-01-15T10:30:00Z" | format_date: "%B %d, %Y at %I:%M %p" }}
{{ "now" | format_date: "%A, %Y-%m-%d" }}

<!-- Output -->
January 15, 2024 at 10:30 AM
Monday, 2024-01-15

Filter Chaining

Filters can be chained together for complex transformations:

{{ code | dedent | format_lang: "python" | highlight: "def" }}

{{ user_input | strip | truncate: 100 | capitalize }}

{{ data | to_json | indent: 2 }}

{{ filename | basename | slugify | append: ".md" }}

Error Handling

Custom filters handle errors gracefully:

Invalid input: Returns original value or empty string
Missing arguments: Uses sensible defaults
Type mismatches: Attempts conversion or returns original value

Performance Notes

Hash filters (md5, sha1, sha256) are computationally expensive for large inputs
Data transformation filters (JSON, CSV, YAML) may consume memory for large datasets
Text processing filters are optimized for typical prompt content sizes
Code filters use efficient parsing algorithms

Integration Examples

Code Review Prompt

# Code Review: {{ filename | basename }}

## File Information
- **Path**: {{ filepath }}
- **Lines**: {{ code | count_lines }}
- **Language**: {{ language | capitalize }}

## Code to Review
{{ code | dedent | format_lang: language }}

## Functions Found
{{ code | extract_functions | bullet_list }}

## Review Checklist
{% assign hash = code | sha256 | truncate: 8 %}
- [ ] Security review (ID: {{ hash }})
- [ ] Performance analysis
- [ ] Style compliance

Data Analysis Prompt

# Data Analysis Report

## Dataset Summary
{% assign data = csv_data | from_csv %}
- **Records**: {{ data | size }}
- **Generated**: {{ "now" | format_date: "%Y-%m-%d %H:%M" }}

## Sample Data
{% for row in data limit:3 %}
{{ forloop.index | ordinal }} record: {{ row | to_json }}
{% endfor %}

## Field Analysis
{% assign fields = data[0] | keys %}
Available fields: {{ fields | bullet_list }}

Documentation Generator

# API Documentation

## Endpoints
{% for endpoint in api_endpoints %}
### {{ endpoint.method | upcase }} {{ endpoint.path }}

{{ endpoint.description | word_wrap: 80 }}

{% if endpoint.parameters %}
**Parameters:**
{{ endpoint.parameters | to_yaml | indent: 2 }}
{% endif %}

**Example:**
```{{ endpoint.language | default: "bash" }}
{{ endpoint.example | dedent }}

{% endfor %}

Generated on {{ “now” | format_date: “%B %d, %Y” }}


## See Also

- [Template Variables](./template-variables.md) - Basic Liquid syntax
- [Advanced Prompts](./advanced-prompts.md) - Using filters in complex templates
- [Testing Guide](./testing-guide.md) - Testing templates with custom filters

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