About regexguide.com
regexguide.com is a modern regex explainer and reference, built for developers who want to understand a regex — not just test it.
Why this site exists
Regex testers like regex101.com are excellent at what they do: real-time testing, multiple flavors, code generation. But they answer one question — does it work? — while leaving another mostly unanswered: what does this pattern someone else wrote actually do?
We built regexguide.com to fill that gap. Paste any regex and get a clear, plain-English breakdown that leads with intent ("this matches an email address") and follows with structured token-by-token detail. No AI hallucinations, no verbose auto-generated walls of text — just clear explanations.
What's here
- The explainer — paste a regex, get a plain-English breakdown
- The patterns library — 200+ curated, rigorously tested patterns for common use cases
- The cheat sheet — every regex token, character class, and flag on one printable page
- Guides — long-form articles explaining the parts of regex most people Google repeatedly
Sister site
regexguide.com is the sister site of crontabsheet.com — a similar tool for cron expressions. Same design language, same focus on clear explanations, same single-developer attention.
How it's built
The whole site is static HTML, CSS, and JavaScript. There is no backend. The regex parser, explainer, and tester all run in your browser. Your regex never leaves your device.
The parser is a hand-written recursive-descent implementation in plain JavaScript — no dependencies, no build step. We wrote it from scratch rather than using an existing library so we could shape the AST specifically for the explanation task.
Open invitations
Found a regex our explainer doesn't handle well? A pattern in our library that fails on a real-world edge case? An explanation that could be clearer? Tell us — those are the highest-value reports we can receive.