About RegexQuill

RegexQuill grew out of the questions people ask about a regex: does it match what I think it matches, what does this part mean, how do I write it in another language, and could it hang my server? Each tool answers one of them, and they share colours and links so a pattern can move from one to the next.

How it works

Everything runs in your browser. Patterns are parsed with regexpp, the open-source ECMAScript regex parser that ESLint uses, which drives the syntax colours, explanations, railroad diagrams, code translation and ReDoS heuristics. Matching, replacing and timing use your browser’s own RegExp engine inside a Web Worker, so results are exactly what your JavaScript would produce, and a runaway pattern can be stopped without freezing the page.

Nothing you type is uploaded: there are no accounts and no server-side processing. The site uses Cloudflare Web Analytics, which counts page views without cookies or cross-site tracking and never receives what you type, paste or drop into the tools. The privacy page has the details.

What it is not

The tester and explainer follow JavaScript. The code export translates patterns for Python, PHP, Go and Java and points out differences it knows about, but it does not run those engines; test the final pattern in the language you ship it in. The ReDoS checker uses heuristics and timing, not a formal proof.

Credits

• Parser: @eslint-community/regexpp (MIT licence).
• Icons: Lucide (ISC licence).
• Type: Newsreader and Source Code Pro (SIL Open Font Licence), served from this site.
• The semantic version pattern in the library is the one published on semver.org; the email pattern is the one in the HTML standard.