Regex Explainer

Frequently Asked Questions

How is this different from regex101?

regex101 gives you a tokenizer view and live match testing — fantastic for building regex. This tool gives you a plain-English walkthrough of what a regex does, which is faster when you just need to understand a regex someone else wrote. Use both: regex101 to iterate, this tool to read.

Does it handle lookbehinds and named groups?

Yes. Named groups (<code>(?&lt;name&gt;...)</code>), lookaheads (<code>(?=...)</code>), negative lookaheads (<code>(?!...)</code>), lookbehinds (<code>(?&lt;=...)</code>), and negative lookbehinds are all explained. It also flags when a lookbehind might not work in older regex engines (JavaScript pre-ES2018, for example).

Will it tell me if my regex is wrong?

It will tell you what the regex matches, and if that doesn't match what you meant, you'll know. For vulnerability checks (ReDoS, catastrophic backtracking) the tool flags obviously risky patterns but isn't a substitute for a dedicated static analyzer.

Which regex flavor does the explanation assume?

The tool infers the flavor from syntax cues. <code>(?&lt;=...)</code> suggests PCRE or modern JS. <code>\d</code> is ambiguous. Python-specific syntax like <code>(?P&lt;name&gt;...)</code> is recognized. If you need a specific flavor called out, mention it in your paste.