API Available

Regex Tester - Live Matching & Highlighting

Test regular expressions with live matching and highlighting. Supports all flags and capture groups. Free online regex debugger.

//g
/.*/gi

Enter a pattern and test string to start matching

Test regular expressions online

Test and debug regex patterns with instant visual feedback. Matches are highlighted in your test string as you type. Supports global, case-insensitive, and multiline flags. A great tool for developers and data analysts.

The tester uses JavaScript's native RegExp engine to evaluate patterns against your test string in real time. It supports all standard regex features: character classes, quantifiers, anchors, groups, lookaheads, lookbehinds, and named capture groups. Flags (global, case-insensitive, multiline, dotAll, sticky, unicode) modify matching behavior.

Regular expressions are used for form validation (email, phone, postal code patterns), log file analysis (extracting timestamps, IP addresses, error codes), data cleaning (removing unwanted characters, normalizing formats), search and replace operations in text editors, web scraping (extracting specific content from HTML), and routing in web frameworks.

Start with simple patterns and build complexity gradually. Use non-capturing groups (?:...) when you don't need to extract the match. Be cautious with greedy quantifiers (.* can match too much) - use lazy versions (.*?) when appropriate. Always test edge cases: empty strings, very long inputs, and strings with special characters. Catastrophic backtracking (e.g., (a+)+ on long strings) can freeze your browser.

Regex101.com is the most popular regex tester with explanation features and a pattern library. Regexr.com offers a visual debugger. This tool provides a clean, distraction-free testing environment with instant highlighting and group extraction, running entirely in your browser. For regex learning, pair it with a cheat sheet - regex syntax is consistent across most programming languages.

How the Regex Tester Works

  1. 01Enter your regular expression pattern in the pattern field
  2. 02Set flags (global, case-insensitive, multiline) as needed
  3. 03Paste or type test text in the input area
  4. 04Matching text is highlighted in real time
  5. 05Captured groups are displayed separately for inspection

Regular Expression Tips

Regular expressions (regex) are powerful patterns for matching and extracting text. Start simple: \d matches any digit, \w matches word characters, . matches any character. Use quantifiers: * (zero or more), + (one or more), ? (optional). Common patterns: email validation, phone numbers, and URL extraction. Always test with edge cases - regex that works on happy paths often fails on unexpected input.

When to Use a Regex Tester

Use this regex tester when building or debugging regular expressions for form validation, data parsing, search-and-replace, or log analysis. Interactive testing is much faster than embedding patterns in code.

Common Use Cases

  • Build and test email validation patterns before implementing in form code
  • Extract data from log files by matching timestamps, IP addresses, and error codes
  • Create search-and-replace patterns for bulk text transformations → Diff Checker
  • Validate input formats like phone numbers, postal codes, and credit card numbers
  • Parse structured text (CSV, log files, URLs) into components using capture groups

Expert Tips

  • Start simple and build complexity gradually - test each part of your pattern before combining them
  • Use non-capturing groups (?:...) when you need grouping for alternation but don't need to extract the match
  • Be cautious with greedy quantifiers like .* - use lazy versions .*? to match as little as possible and avoid unexpected results

Frequently Asked Questions

What is a regular expression?→
A regular expression is a pattern describing a set of strings. For example, \d{3}-\d{4} matches patterns like 123-4567. Regex is supported in virtually every programming language.
What do the flags g, i, m mean?→
g (global) finds all matches. i (case-insensitive) ignores case. m (multiline) makes ^ and $ match line boundaries. Combine them: gi finds all matches case-insensitively.
How do I match an email with regex?→
A simple pattern: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}. For production, validate basic format with regex then confirm via verification email.
Is my data private?→
Yes, all testing happens locally in your browser using JavaScript RegExp. No patterns or test strings are sent to any server.

Related tools

12 suggested
Sponsored tools
VultrSponsored

High-performance cloud servers from $2.50 per month.

Visit Vultr →

Link to this tool

Free to use, free to link

Mentioning this tool in a README, a blog post or your team wiki? Paste one of these and your readers land straight on the tool, running in their own browser.

  • HTML<a href="https://toolforte.com/tools/regex-tester">Regex Tester</a>
  • MD[Regex Tester](https://toolforte.com/tools/regex-tester)