regex-tester skill

Overview

This skill lets you test and debug regular expressions interactively, with match highlighting, capture group extraction, and a library of common patterns. It focuses on fast feedback so you can validate patterns, inspect groups, and iterate quickly. The tool supports finding all matches and applying named or built-in patterns for common use cases.

How this skill works

Provide a regex and an input string; the tool runs the pattern against the text and returns highlighted matches plus details for each capture group. Options let you list all matches, show group contents, and choose a common pattern from the built-in library (email, URL, digits, etc.). Results include match spans and extracted text to help diagnose why a pattern does or does not match.

When to use it

• Validating a new regex before adding it to production code
• Debugging why a capture group returns empty or unexpected values
• Searching a text sample for all occurrences of a pattern
• Quickly applying common patterns (email, URL, IP) without writing them from scratch
• Learning regex behavior by inspecting matches and spans

Best practices

• Start with a minimal pattern and expand once matches behave as expected
• Use the capture group view to confirm group boundaries and contents
• Test edge cases and multiline inputs to ensure anchors and flags work
• Prefer explicit character classes and quantifiers to avoid catastrophic backtracking
• Select a common built-in pattern when available to reduce mistakes

Example use cases

• Highlight all 4-letter words in a sentence to verify boundary anchors
• Extract username and domain from email strings using capture groups
• Find every sequence of digits in log entries for downstream processing
• Validate that a user-supplied pattern matches only intended formats
• Swap between a custom pattern and a built-in email pattern to compare results

FAQ