Create and Save Custom Regex Patterns for Reuse

While ListWrangler includes many pre-built patterns for common data types, sometimes you need patterns tailored to your specific data. The Pattern Builder lets you create, test, and save custom patterns for future use.

What You’ll Learn

In this guide, you’ll discover how to:

• Use the Pattern Builder interface
• Create custom regex patterns step-by-step
• Test and validate patterns before saving
• Save patterns for future sessions
• Import and export pattern collections
• Manage your custom pattern library

Why Create Custom Patterns?

Custom patterns are valuable when you need to:

• Match proprietary formats (internal codes, custom IDs)
• Handle industry-specific data (medical codes, legal citations)
• Adapt to your data (specific date formats, naming conventions)
• Reuse complex patterns without rewriting them each time
• Share patterns with team members

Step 1: Open the Pattern Builder

1. Click Find & Replace in the toolbar
2. Select the Builder tab at the top
3. You’ll see the pattern creation interface

Step 2: Build Your Pattern

The Pattern Builder provides a structured way to create regex patterns:

Pattern Input Field

Enter your regex pattern in the main input field. The builder validates your pattern in real-time.

Validation Feedback

• Green checkmark: Pattern is valid
• Red warning: Pattern has syntax errors
• Match count: Shows how many matches found in current text

Testing Area

Your current list content is used as the test data. As you type your pattern, matches are highlighted.

Creating Patterns: Step-by-Step Examples

Example 1: Product SKU Pattern

Suppose your product SKUs follow the format: ABC-12345-XY

Pattern: [A-Z]{3}-\d{5}-[A-Z]{2}

Breaking it down:

• [A-Z]{3} - Exactly 3 uppercase letters
• - - Literal dash
• \d{5} - Exactly 5 digits
• - - Literal dash
• [A-Z]{2} - Exactly 2 uppercase letters

Example 2: Employee ID Pattern

Employee IDs in format: EMP001234

Pattern: EMP\d{6}

Breaking it down:

• EMP - Literal text “EMP”
• \d{6} - Exactly 6 digits

Example 3: Custom Date Format

Dates in format: 15-Jan-2025

Pattern: \d{2}-[A-Z][a-z]{2}-\d{4}

Breaking it down:

• \d{2} - Two digits (day)
• - - Literal dash
• [A-Z][a-z]{2} - Capitalized month abbreviation
• - - Literal dash
• \d{4} - Four digits (year)

Example 4: Version Numbers

Software versions like: v2.1.0, v10.5.23

Pattern: v\d+\.\d+\.\d+

Breaking it down:

• v - Literal “v”
• \d+ - One or more digits (major)
• \. - Literal period (escaped)
• \d+ - One or more digits (minor)
• \. - Literal period
• \d+ - One or more digits (patch)

Example 5: Hashtags

Social media hashtags: #ListWrangler

Pattern: #[A-Za-z]\w*

Breaking it down:

• # - Literal hash symbol
• [A-Za-z] - Must start with a letter
• \w* - Followed by any word characters

Step 3: Test Your Pattern

Before saving, thoroughly test your pattern:

1. Check match count: Ensure the number of matches is expected
2. Review edge cases: Test with variations of your data
3. Verify no false positives: Make sure it doesn’t match unwanted text
4. Verify no false negatives: Make sure it catches all valid matches

Testing Tips

• Add sample data to your list specifically for testing
• Include both valid and invalid examples
• Test boundary cases (shortest and longest valid inputs)
• Check for partial matches that shouldn’t occur

Step 4: Save Your Pattern

Once your pattern works correctly:

1. Click Save Pattern button
2. Enter a Name for your pattern (e.g., “Product SKU”)
3. Select or create a Category (e.g., “Business”, “Custom”)
4. Add an optional Description explaining what it matches
5. Click Save

Your pattern is now saved in your browser’s local storage.

Managing Custom Patterns

Access Saved Patterns

1. Go to Pattern Mode (Pattern tab)
2. Your custom patterns appear alongside built-in patterns
3. Custom patterns are marked with a special icon

Edit Existing Patterns

1. Select your custom pattern
2. Click the Edit button
3. Modify the pattern, name, or description
4. Save your changes

Delete Patterns

1. Select the pattern to remove
2. Click the Delete button
3. Confirm deletion

Note: Deleted patterns cannot be recovered unless you have an export backup.

Import and Export Patterns

Export Your Patterns

Share patterns with others or back them up:

1. Go to Pattern Mode settings
2. Click Export Patterns
3. A JSON file downloads with all your custom patterns

Import Patterns

Add patterns from colleagues or restore from backup:

1. Click Import Patterns
2. Select a JSON pattern file
3. Review the patterns being imported
4. Confirm import

Import Validation

ListWrangler validates imported patterns for safety:

• Patterns are checked for valid regex syntax
• Potentially dangerous patterns are flagged
• You can review before accepting imports

Best Practices for Custom Patterns

1. Use Descriptive Names

Name patterns clearly: “Invoice Number” not “Pattern 1”

2. Add Helpful Descriptions

Include format examples: “Matches ABC-12345 format”

3. Organize by Category

Group related patterns: “Finance”, “HR”, “Products”

4. Test Thoroughly

Validate against real data before saving

5. Document Edge Cases

Note any limitations in the description

6. Regular Backups

Export your patterns periodically

Pattern Building Reference

Common Pattern Components

Component	Pattern	Matches
Any digit	\d	0-9
Any letter	[a-zA-Z]	a-z, A-Z
Word character	\w	a-z, A-Z, 0-9, _
Whitespace	\s	Space, tab, newline
Any character	.	Anything except newline
Literal special char	\. \* \+	. * +

Quantifiers Quick Reference

Quantifier	Meaning
*	0 or more
+	1 or more
?	0 or 1
{n}	Exactly n
{n,}	n or more
{n,m}	Between n and m

Troubleshooting Custom Patterns

Pattern Won’t Save

• Check for syntax errors (red validation warning)
• Ensure name field is filled
• Try a shorter pattern name

Pattern Not Matching Expected Text

• Verify regex mode is enabled
• Check case sensitivity
• Test with simpler version first

Imported Patterns Not Appearing

• Ensure JSON file is valid
• Check for duplicate pattern names
• Verify pattern passed security validation

What’s Next?

Put your custom patterns to work:

• Extract Data - Use patterns to extract data
• Mask Sensitive Data - Redact matched content
• Advanced Regex - Learn more regex techniques

Frequently Asked Questions

Are my patterns saved permanently?

Custom patterns are saved in your browser’s local storage. They persist across sessions but are browser-specific. Export regularly for backup.

Can I share patterns with my team?

Yes! Export your patterns to a JSON file and share it. Team members can import the file to get your patterns.

Is there a limit to how many patterns I can save?

No hard limit, but browser storage has limits. Keep your library organized and remove unused patterns.

Will patterns work across different browsers?

Patterns are standard JavaScript regex, so they work the same everywhere. However, saved patterns are browser-specific. Use export/import to transfer between browsers.

Can I edit built-in patterns?

Built-in patterns cannot be edited, but you can create a custom copy with modifications.