Regex Tester & Explainer

This regex tester runs your pattern against real text as you type, using the JavaScript (ECMAScript) engine — the same flavor that runs in every browser and in Node.js. Matches are highlighted directly inside the test string, and each one appears in a match list with its character index and every capture group, both numbered ($1, $2…) and named ((?<name>…)). All six JS flags — g, i, m, s, u and y — toggle with one tap.

It goes well beyond matching. A Replace panel previews String.replace() output with $1, $2 and $& substitutions. An export bar copies every match and its groups as JSON or CSV, ready for a spreadsheet or script. The Explain tab breaks the pattern into tokens and describes each one in plain English, and the Cheatsheet tab pairs a syntax reference with tap-to-load presets for emails, URLs, IPv4 addresses, hex colors, dates, phone numbers and more. A Share button packs the pattern, flags and sample text into a link you can send to a teammate.

Your text never leaves the browser, and a built-in safety net makes the tester hard to freeze: patterns with classic catastrophic-backtracking signatures (like nested quantifiers) are detected and tested against a reduced sample, very large inputs are capped, and matching runs under a one-second budget — so even a hostile regex can't lock up the page.