A regex tool that speaks plain English in both directions — read any pattern back token by token, or forge a new one from what you actually want to match.
Regular expressions are write-once, read-never. You paste one from a Stack Overflow answer, it works, and six months later nobody — including you — can say what it does or safely change it. Most online testers only tell you whether it matched, not why.
patternsmith closes that gap from both sides. Explain takes a regex and narrates every anchor, class, quantifier, group and backreference in plain words, with a one-line summary. Build goes the other way: pick an intent (email, URL, ISO date, phone, UUID…) or stack composable blocks, and watch a working pattern assemble itself, each step narrated. A live tester highlights matches, fills a captured-groups table, and previews replacements as you type — and it all runs on your machine, so you can paste real data without it leaving the browser.
npm install # install dependencies
npm run dev # local dev server with hot reload
npm run build # build the static site to ./dist/npm run preview serves the production build locally. The site is fully static and deploys under a base path (GitHub Pages); every asset and link is referenced through import.meta.env.BASE_URL, so nothing 404s under the base.
- 100% client-side. Native
RegExponly. A strict Content-Security-Policy withconnect-src 'none'is enforced via a<meta>tag — nothing you type is ever sent anywhere. Your pattern and sample live in the URL hash, so a link is shareable without a server. - Can't hang the page. Matching runs in a Web Worker behind a wall-clock time cap. A catastrophic-backtracking pattern such as
/(a+)+$/gets the worker terminated and a friendly "too slow" message instead of a frozen tab.
This software is provided "as is", without warranty of any kind, express or implied. It is a learning and productivity aid, not a validation authority: verify every generated or explained pattern against your own real inputs before relying on it in production. Regex behaviour varies across engines, and an explanation or a generated pattern may not fit your exact case. To the maximum extent permitted by law, the author accepts no liability for any loss or damage arising from use of this tool or the patterns it produces. See LICENSE for the full MIT terms.
MIT © 2026 Sreenivas Sadhu Prabhakara. See LICENSE.