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Regex Tester & Generator — User Guide

The Regex Tester & Generator is a powerful developer utility for crafting, testing, debugging, and explaining regular expressions. Everything runs 100% locally in your browser using standard JavaScript regex specifications with instant visual feedback.

Interactive Tool Modes

1. Match & Test (Live Highlighting)

  • Live Visual Highlighting: Matched substrings are dynamically highlighted directly inside the test text container.
  • Categorized Presets Library: 15+ pre-built regex patterns grouped by domain:
    • Web & Network: Emails, URLs, IPv4 addresses, domain names, HTML tags.
    • Auth & Identity: JWT tokens, UUID v4, strong password policies, URL slugs.
    • Data & Formats: Hex colors, ISO dates, 24-hour time, US phone numbers, credit card numbers.
    • Code & Syntax: Single-line/multi-line comments, ES6 import statements.
  • Flags Toggle: Toggle standard flags (g global, i ignore case, m multiline, s dotAll, u unicode, y sticky).
  • Quick Token Insertion Bar: 1-click insertion for common regex tokens (\d, \w, \s, \b, [a-z], (?=...), ^...$).
  • Match Breakdown Cards: Detailed breakdown of every match showing character range indices, match length, captured group numbers ($1, $2), and named capture groups (<name>).

2. Find & Replace

  • Test regex substitution strings supporting special replacement variables:
    • $1, $2 ... captured groups
    • $& matched substring
    • $ followed by group name
  • Instant preview of replaced string output with 1-click copy and file download.

3. Regex Explainer (Pattern Deconstruction)

  • Translates complex regex syntax into human-readable plain English steps:
    • Anchors (^, $, \b)
    • Character Classes (\d, \w, \s, .)
    • Quantifiers (*, +, ?, {n,m})
    • Groups & Lookarounds ((...), (?:...), (?=...), (?<=...))
    • Character Sets ([...], [^...])

4. Code Snippet Generator

  • Export production-ready code snippets in 7 programming languages:
    • JavaScript / TypeScript (new RegExp(), matchAll())
    • Python (re module, re.finditer())
    • PHP (preg_match_all())
    • Go (regexp.MustCompile())
    • Java (Pattern and Matcher)
    • C# / .NET (Regex.Matches())
    • Rust (regex::Regex)

5. Cheat Sheet & Reference

  • Filterable and searchable quick-reference guide for regex tokens, quantifiers, lookarounds, and syntax. Click any token to insert it into your active pattern.

Safety & Performance

  • ReDoS Protection: Pattern match iteration is capped at 10,000 iterations to prevent infinite loops from zero-width matches or exponential catastrophic backtracking.
  • Client-Side Privacy: Test string data and regular expressions never leave your browser.