Free Online Regex Tester & Debugger — JavaScript Regular Expression Tool

Overview: Test & Debug Regular Expressions with Live Match Highlighting

Real-time JavaScript regular expression matcher, capture group inspector table, and regex replace debugger. All computations and data processing are executed 100% locally on your device using client-side WebAssembly, HTML5 Canvas, and modern Web APIs without uploading files to any external server.

Supported Formats

Regex Tester & Debugger supports the following file formats:

  • .regex — client-side processing support.
  • .txt — client-side processing support.

How to Use Regex Tester & Debugger in Browser

  1. Enter Regex: Type your regular expression and select flags (g, i, m, s).
  2. Insert Test Text: Paste the text you want to test against.
  3. Review Matches: Inspect match indices, lengths, and captured groups.

Key Features & Privacy Protections

  • 100% Client-Side Privacy: Zero cloud upload. Your documents, photos, and files never leave your local browser sandbox.
  • Zero Installation: Runs instantly in Chrome, Safari, Firefox, Edge, Android, and iOS browsers.
  • Free Forever: No sign-up, no subscriptions, no ads, and no file size limits.

Frequently Asked Questions (FAQ)

Which regular expression flags are supported?

Supports Global (g), Case-insensitive (i), Multiline (m), and DotAll (s) flags.

Does it display captured match groups ($1, $2)?

Yes, the match table provides an exact breakdown of full match text, match index, match length, and all captured sub-groups.

Can I test replacement strings with capture tokens?

Yes, switch to the 'Regex Replace' tab to test replacements using $1, $2, and custom text with instant output preview.

Does it include pre-built regex patterns?

Yes, click on pre-built shortcuts for Email, URL, IPv4, Hex Color, and Date (YYYY-MM-DD) to test instantly.

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Regex Tester & Debugger

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v1.0.0Free · RegExp EngineDeveloper Tools

Free Online Regex Tester & Debugger — JavaScript Regular Expression Tool

Test & Debug Regular Expressions with Live Match Highlighting. Real-time JavaScript regular expression matcher, capture group inspector table, and regex replace debugger.

What is Regex Tester and what does it do?

The Regular Expression Tester & Debugger is an interactive developer tool designed to construct, validate, and test JavaScript and PCRE-compatible regular expressions against sample text in real time.

Featuring visual match highlighting, named capture group inspection, replacement string testing, and a comprehensive quick-reference cheat sheet, it simplifies the process of mastering complex regex patterns directly in your browser.

  • Real-time regex evaluation against sample test strings with instant visual match highlighting.
  • Interactive flag toggles: Global (g), Multiline (m), Case Insensitive (i), DotAll (s), and Unicode (u).
  • Detailed capture group inspector displaying match indices, full match text, and numbered or named capture groups.
  • Live string replacement simulator supporting substitution tokens ($1, $&, $<name>).
  • Built-in regex cheat sheet covering anchors, character classes, quantifiers, lookaheads, and common patterns.

How does Regex Tester work?

The tool compiles your pattern and selected flags into a native JavaScript RegExp instance. Input text is scanned iteratively to record character offsets, matched substrings, and capture group arrays.

Matched slices are wrapped in highlighted visual spans, and replacement patterns are evaluated against the source text to demonstrate transformation outcomes in real time.

100% private: all processing happens locally in your browser using client-side WebAssembly, HTML5 Canvas, and modern Web APIs. Your files are never uploaded to any server.

Who needs Regex Tester?

Backend & Full-Stack Developers

Build and test robust validation expressions for emails, phone numbers, UUIDs, and complex data sanitization.

Data Engineers & Scrapers

Formulate precise extraction patterns to harvest structured fields, log entries, and web scraping tokens.

QA Automation Engineers

Verify assertion patterns and regex-based test validations across automated test suites.

Computer Science Students

Learn regular expression mechanics, capture groups, and boundary assertions through interactive visual experimentation.

Supported file formats

Regex Tester & Debugger processes the following file extensions and data formats directly in your browser:

.regex.txt

How to use Regex Tester — step by step

  1. 1

    Enter Regex

    Type your regular expression and select flags (g, i, m, s).

  2. 2

    Insert Test Text

    Paste the text you want to test against.

  3. 3

    Review Matches

    Inspect match indices, lengths, and captured groups.

Frequently asked questions

Which regular expression flags are supported?

Supports Global (g), Case-insensitive (i), Multiline (m), and DotAll (s) flags.

Does it display captured match groups ($1, $2)?

Yes, the match table provides an exact breakdown of full match text, match index, match length, and all captured sub-groups.

Can I test replacement strings with capture tokens?

Yes, switch to the 'Regex Replace' tab to test replacements using $1, $2, and custom text with instant output preview.

Does it include pre-built regex patterns?

Yes, click on pre-built shortcuts for Email, URL, IPv4, Hex Color, and Date (YYYY-MM-DD) to test instantly.

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