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Regex Tester & Explainer

Test, visualize, debug, and explain regular expressions in plain English with instant match highlighting.

Formatters & Utilities
Privacy: 100% Client-Side. Your data never leaves this browser tab. Processing uses Web APIs and client-side libraries only.

100% client-side regex tester with capture-group highlighting, plain-English explanations, presets, and multi-language export. Matches run in a Web Worker with a timeout to mitigate ReDoS.

Common patterns

//gm
0 matches

Highlighted matches

[email protected] bad@@mail [email protected]
full match$1$2$3$4

What is a regular expression?

A regular expression (regex) is a compact pattern language for searching and validating text — emails, UUIDs, URLs, log lines, and more. Developers use them in forms, parsers, linters, and security filters.

This workbench lets you edit a pattern with flags (g/i/m/s/u), highlight matches and capture groups against a test string, read a plain-English breakdown of the pattern, insert common presets, and export snippets for multiple languages. Matching runs in a Web Worker with a timeout to reduce ReDoS risk.

How to use this tool

  1. Pick a preset (Email, UUID, IPv4, …) or paste your own pattern and toggle flags.
  2. Enter a test string and inspect color-coded matches plus the groups table.
  3. Open Explainer for a token-by-token English breakdown, Builder to generate a class-based pattern, or Export to copy JS/Python/Go/Java/PHP/Rust snippets.

Frequently asked questions

Is my regex or test data sent to a server?

No. Pattern parsing, explanation, and matching all run in your browser. Nothing is uploaded.

How do you mitigate ReDoS?

Matches execute in a Web Worker with a short timeout. Pathological patterns that hang are aborted with a timeout message instead of freezing the UI.

Is the explainer a full ECMAScript parser?

It covers common constructs (groups, classes, quantifiers, anchors, escapes, alternation) for learning and debugging. Exotic or vendor-specific syntax may be summarized approximately — always trust the JS engine for exact behavior.