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/build-regex - Build Regular Expression

Build a regular expression pattern from a natural language description.

Claude Code Knowledge Pack7/10/2026

Overview

/build-regex - Build Regular Expression

Build a regular expression pattern from a natural language description.

Steps

  1. Ask the user to describe the pattern they want to match in plain language
  2. Identify the key components: literal strings, character classes, repetition, groups
  3. Determine the regex flavor: JavaScript, Python, Go, Java, PCRE
  4. Build the regex pattern incrementally, starting with the simplest matching version
  5. Add anchors (^, $) if the pattern should match the entire string
  6. Use named capture groups for extracting specific parts
  7. Add quantifiers: exact counts, ranges, greedy vs lazy matching
  8. Handle edge cases: optional parts, alternatives, escaped special characters
  9. Add lookahead/lookbehind assertions if needed for context-dependent matching
  10. Optimize the regex for performance: avoid catastrophic backtracking
  11. Provide a plain-English explanation of what the regex matches
  12. Show the regex with inline comments explaining each part

Rules

  • Start with the simplest pattern that works and add complexity only as needed
  • Use non-capturing groups (?:) unless capture is explicitly needed
  • Prefer character classes [a-z] over alternation (a|b|c) for single characters
  • Avoid nested quantifiers that can cause catastrophic backtracking
  • Use named groups for clarity in complex patterns
  • Test the regex against edge cases including empty strings
  • Provide the pattern in the correct syntax for the target language