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Regular Expression Tester

Interactive regular expression tester with live highlighting, capture group inspection, and flag controls.

Flags
gFind all matches in the test string.
Current PatternEnter a pattern to begin testing.

Match Preview

Matches will be highlighted here once the pattern finds results.

Match Details

No matches found.

Common Regex Presets

Load a preset to explore typical matching scenarios.

ISO Date (YYYY-MM-DD)

Captures year, month, and day segments from ISO-style dates.

Pattern(\d{4})-(\d{2})-(\d{2})
Flagsg
Test TextOrder date: 2023-10-05 Backup: 2024-01-14
Email With Named Groups

Extract the username and domain parts from email addresses using named groups.

Pattern(?<user>[\w.+-]+)@(?<domain>[\w-]+\.[A-Za-z]{2,})
Flagsgi
Test TextSupport: help(at)example.com Sales: careers(at)my-shop.co
IPv4 Address

Matches IPv4 addresses with strict 0-255 validation for each octet.

Pattern\b(?:(?:25[0-5]|2[0-4]\d|1?\d?\d)\.){3}(?:25[0-5]|2[0-4]\d|1?\d?\d)\b
Flagsg
Test TextPrimary: 192.168.0.1, Backup: 10.0.24.16
Hex Color

Finds shorthand and full hexadecimal color codes.

Pattern#(?:[0-9a-fA-F]{3}){1,2}\b
Flagsg
Test TextPalette: #fff, #0fb981, #1f2937
HTML Opening Tag

Validates simple HTML opening tags with basic attribute pairs.

Pattern^<([a-z]+)(?:\s+[a-z-]+="[^"]*")*>$
Flagsim
Test Text&lt;div class="card"&gt; &lt;input type="text" disabled&gt;

Tool Overview: Regex Tester & Debugger Guide

The Regex Tester helps you design, verify and debug JavaScript regular expressions without writing any boilerplate code. Type or paste a pattern, flip the supported flags (g, i, m, s, u, y), and the tool immediately highlights every match, capture group and named group inside your sample text.

What Is Regex Tester & Debugger Guide?

Regex Tester & Debugger Guide quickly tests rules or connections to help locate issues.

How to Use

  1. Enter rules or parameters.
  2. Provide sample input or a target address.
  3. Review results and adjust.

Common Use Cases

  • Pre-release checks and debugging
  • Validate rules and edge cases
  • Quick verification during integration

❓ FAQ

Q1: Results not as expected?
A: Check input and options.

Q2: Test failed?
A: Simplify the case to isolate the issue.

Q3: How to save output?
A: Copy the results or take a snapshot.

Why Use This Tool?

  • Faster iteration – tweak the pattern and flags and see results instantly, including error messages for invalid syntax.
  • Visual feedback – zero-width matches, multi-line matches and group boundaries are highlighted so complex expressions become easier to reason about.
  • Built-in examples – one-click presets cover common tasks such as ISO dates, email addresses, IPv4 addresses, hex colours and HTML tags.
  • SEO & data validation – perfect for copywriters, developers and QA engineers who need to validate content before it goes live.

Quick Start Checklist

  1. Enter or paste your regex pattern in the first field, for example (?<user>[\w.+-]+)@(?<domain>[\w-]+\.[A-Za-z]{2,}).
  2. Supply sample text in the Test String area.
  3. Enable or disable flags under Flags to switch between global, case-insensitive, multiline and other matching modes.
  4. Review the Match Preview panel to see highlighted matches inside the source text.
  5. Scroll to Match Details to inspect positions, lengths and extracted groups.

Flag Reference

Flag Name Primary Use Case
g Global Return all matches instead of stopping at the first.
i Ignore Case Match uppercase and lowercase characters equally.
m Multiline Make ^ and $ anchor to line breaks as well.
s Dot All Allow the dot (.) to match newline characters.
u Unicode Enable full Unicode code point awareness.
y Sticky Continue matching from the last index only.

Example Library

The examples panel contains curated presets you can load instantly. Each preset swaps in a ready-to-use pattern, test data and recommended flag combination:

  • ISO Date (YYYY-MM-DD) – capture year, month and day components for content validation or analytics pipelines.
  • Email With Named Groups – extract user and domain portions with friendly group names for form validation.
  • IPv4 Address – verify network configuration strings while ensuring each octet falls within 0-255.
  • Hex Colour – detect short (#fff) and long (#0fb981) CSS colour declarations.
  • HTML Opening Tag – confirm that a snippet contains a valid opening tag with basic attribute/value pairs.

Expert Tips

  • Watch for the zero-width warning. Add quantifiers that consume characters (+, *, {n,}) when appropriate to avoid infinite loops.
  • When copying patterns into JavaScript code, remember to escape backslashes: \d inside the tester becomes \\d in a string literal.
  • Use named capture groups ((?<name>...)) to make the Match Details table more readable and integration-friendly.
  • Combine this tester with other ToolMi utilities (such as the JSON to YAML converter or Markdown formatter) to streamline publishing workflows.

FAQ

Does the tester support lookaheads and lookbehinds?
Yes. The engine is the same as JavaScript (ECMAScript) regular expressions, so positive/negative lookarounds, Unicode property escapes and backreferences are supported.

Can I share my pattern with teammates?
Use the preset copy button in the examples panel or export your pattern and sample text to a shared document. ToolMi does not currently generate shareable URLs.

Why don’t I see matches even though the regex looks correct?
Ensure the correct flags are enabled, trim trailing whitespace from your test string, and confirm the pattern is anchored properly (^, $, word boundaries, etc.).

Additional Resources

With this interactive tester, you can confidently ship regex-powered features, validate SEO copy, or debug complex parsing tasks in seconds.