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Regex Tester and Explainer

Use this regex tester and explainer to debug JavaScript patterns, validate sample matches, inspect capture groups, and understand the pattern before pasting it into code.

Live developer utility

Regex tester and explainer

Flags/gi
Match output
21: ALICE@example.com
43: qa@toolkitshelf.com
Pattern statusValid regex

Compiled with the JavaScript RegExp engine.

Matches2

2 capture groups detected across 81 sample characters.

Match details

Matches are shown in source order. Empty captures are shown as blank group values.

#IndexMatchCapture groups
121ALICE@example.comALICE | example.com
243qa@toolkitshelf.comqa | toolkitshelf.com
Plain-English pattern notes
Pattern note
Word boundary (\b): matches an edge between word and non-word characters.
Word token (\w): matches letters, numbers, and underscores.
Character class ([...]): matches one character from a custom set or range.
Quantifier: repeats the previous token or group.
2 capture groups: captured text is listed for each match.
Warnings and review notes
Review note
Case-insensitive mode is enabled.
Privacy note

Regex testing runs in the browser. Avoid pasting production tokens, private customer data, or credentials into a shared browser session.

Generation method

Regex testing method

Match report = JavaScript RegExp(pattern, flags) + bounded global scan over sample text + capture group extraction + pattern token notes

The tester uses the browser JavaScript regular expression engine. Regex flavor, Unicode handling, lookbehind support, and performance can differ from other languages.

How to use

Steps

  1. Paste a JavaScript regex pattern without the surrounding slash characters.
  2. Choose flags such as g, i, m, s, u, or y.
  3. Paste realistic sample text that includes expected matches and near-misses.
  4. Review match positions, capture groups, warnings, and plain-English pattern notes before using the regex in code.

Example

Sample output

Email pattern\b([\w.%+-]+)@([\w.-]+\.[a-z]{2,})\b
Flagsg and i for global, case-insensitive matching
OutputMatch index, matched text, and captured username/domain groups

Generator use

Best for

  • Browser-side link, file, format, and web utility tasks that need an output now.
  • Generating reusable artifacts such as QR codes, snippets, exports, or cleaned payloads.

Before relying on it

Check first

  • The tester uses the browser JavaScript regular expression engine. Regex flavor, Unicode handling, lookbehind support, and performance can differ from other languages.
  • Publishing a generated file or code without testing it in the real destination.
  • Encoding private or sensitive data into an output that other people can scan, copy, or inspect.

Details

What to know before using the output

Regex flavorJavaScript RegExp

The tester follows the JavaScript regular expression engine used by the browser, not PCRE, Python, Ruby, Go, or database-specific regex flavors.

Capture groupsShown per match

Captured values are listed next to each match so replacement logic, extraction code, and validation patterns are easier to debug.

Safety boundFirst 200 matches

Matching is bounded and zero-length matches advance manually so a pattern cannot lock the browser in an infinite match loop.

Source notes

References used for this generator

MDN Web DocsDocuments JavaScript regular expressions, syntax, assertions, groups, quantifiers, and flags.MDN Web DocsDocuments the RegExp object, flags, match behavior, and browser compatibility.

Benchmarks

How to read the output

g flag: Find all matches.

Use global matching when extraction, replacement, or QA needs every occurrence instead of the first match.

i flag: Ignore case.

Useful for copied text, emails, slugs, and user-entered strings where casing is not meaningful.

Sample text: Include near-misses.

A regex is more trustworthy when it rejects realistic non-matches, not only when it matches the happy path.

Method and limitations

Methodology and assumptions

Formula, inputs, limitations and review record
Generation method

Match report = JavaScript RegExp(pattern, flags) + bounded global scan over sample text + capture group extraction + pattern token notes

Inputs used

Regex pattern, JavaScript flags, Sample text, Matches, Capture groups, Pattern explanation

Limitations

Utility outputs depend on the encoded payload, file format, target app, scanner, printer, browser, and real-world testing before sharing.

Review record

Catalog QA baseline on June 6, 2026. This date marks the catalog-wide automated and editorial QA baseline, not a tool-specific expert review.

Cite this page

Toolkit Shelf. Regex Tester and Explainer. https://toolkitshelf.com/tools/regex-tester-explainer

FAQ

Common questions

Which regex flavor does this tester use?

It uses JavaScript RegExp syntax. Patterns from PCRE, Python, Ruby, Go, SQL, or command-line tools may need changes before they behave the same way.

Why are capture groups important?

Capture groups show the parts of each match that your code can extract or reuse in replacements, such as a username, domain, ID, or date segment.

Does this upload my sample text?

No. The pattern and sample text are tested in the browser. Avoid pasting private credentials, tokens, or customer data into a shared browser session.