What do I need to use Regex Builder & Explainer?

What should match and what should NOT; The engine / flavor; Where it runs.

Is Regex Builder & Explainer free to use?

Yes — run it free in the browser playground (no API key needed for the sponsored trial, or bring any provider key), or install it into Claude Code, Cursor, ChatGPT and more via npx pm-claude-skills. MIT-licensed and open source.

Regex Builder & Explainer

Q: How do I know the Regex Builder & Explainer output is good?

The skill verifies itself against its own quality checks: The pattern actually passes the listed "matches" and rejects the "rejects"; Flavor and flags are stated; The breakdown covers every token, not just the interesting ones; Edge cases / backtracking risks are flagged.

🔵 Stable🕐 updated 2026-10-06 ✅ 4.8/5 🔷 SkillSpec L3 pm-engineering

Build a regular expression from a plain-English description, or explain an existing one. Use when asked to write a regex, match/validate/extract a pattern, or understand what a regex does. Produces the regex, a token-by-token breakdown, passing and failing test cases, and notes on flavor/edge cases.

▶ Run it free — no key needed 📝 Grade your existing draft ⬇ Add to Claude (works in Duet) 📱 Use as an app View SKILL.md ↗ What changed

🗣 Say this to your agent

“Write a regex.”“Match/validate/extract a pattern.”“Understand what a regex does.”

What to give it

▸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.

✅ The bar it holds itself to

Every skill in this library self-verifies — these are this skill's own quality checks, straight from its definition.

✓The pattern actually passes the listed "matches" and rejects the "rejects"

✓Flavor and flags are stated

✓The breakdown covers every token, not just the interesting ones

✓Edge cases / backtracking risks are flagged

⚠️ What it refuses to do

Do not give a regex with no test cases — always prove it

Do not ignore the flavor — `\d`, lookbehind, and named groups differ across engines

Do not produce an unreadable one-liner when a commented/verbose version or a non-regex approach is clearer

Do not silently assume anchoring — state whether it matches the whole string or a substring

Install

npx pm-claude-skills add --agent claude   # or codex · cursor · gemini · hermes
# or one-line MCP (every skill, any client):
claude mcp add pm-skills -- npx -y -p pm-claude-skills pm-claude-skills-mcp

Start with

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🔌 Embed this skill

Drop this on your blog, docs, or site — it renders a "Run this skill" card:

<div data-pm-skill="regex-builder"></div>
<script src="https://mohitagw15856.github.io/pm-claude-skills/embed.js" async></script>

💬 Discussion

Regex Builder & Explainer is one of 1326 open-source professional AI agent skills — all SkillSpec L3. Try them all in the browser · ⭐ Star on GitHub · Browse the full catalog