Regex Builder & Explainer Skill

Produce correct, readable regular expressions — and explain them so the user actually understands what they're shipping.

Working from a brief

Infer the regex flavor (JavaScript/PCRE/Python/Go) from context; if unstated, default to one and say so (assumed — confirm). Always deliver a working pattern and tests even from a loose description. Never leave placeholders.

Required Inputs

• What should match and what should NOT — 3+ positive examples and, critically, 2+ near-miss negatives (the strings that look matchable but must be rejected). The negatives are where every regex bug lives.
• The engine/flavor (JavaScript, PCRE, Python re, RE2, grep -E…) — anchors, lookbehind, and Unicode behaviour differ enough to break portability silently.
• Where it runs — validation, extraction, or replacement changes how greedy the pattern should be.

Two modes

• Build: the user describes what to match → produce the regex.
• Explain: the user pastes a regex → break it down. Detect which from the input.