Awesome Regex curates the best regular expression tools, tutorials, libraries, and other resources. It covers all major regex flavors, and currently includes especially deep coverage of regular expressions in JavaScript.

Regular expressions (regex or regexp) are a powerful and concise way to search, parse, and process text. They're built into many programming languages, text editors, IDEs, database engines, word processors, and other tools.

Contributions are welcome. Add links through pull requests (guidelines) or create an issue to start a discussion.

• Testers
• Syntax-free regex builders
• Visualizers
• Search and replace through files
• Tutorials
  • Videos
• Regex engines
  • Documentation
  • Source code
  • Flavor differences
• Performance
• Collections of patterns
• JavaScript regex libraries
• JavaScript regex evolution
• Books
• Articles
• Communities
• Miscelaneous

For building, testing, and playing with regexes.

• regex101 - Best free and best web-based tester.
  • Flavors: Java, JavaScript, .NET, PCRE, RE2, Rust, and emulates Python.
  • Includes regex debugger (PCRE only).
• RegexBuddy (, $40) - Best tester.
  • Flavors: Emulates hundreds of flavors/versions, with deep knowledge of differences.
  • Includes regex debugger.
• RegExr [GitHub] - Best open source tester.
  • Flavors: JavaScript, PCRE.
  • Languages: 🇺🇸, 🇨🇳 (fork).
• RegexLearn [GitHub] - Best multilingual tester (JavaScript).
  • Languages: 🇺🇸, 🇹🇷, 🇷🇺, 🇪🇸, 🇨🇳, 🇩🇪, 🇺🇦, 🇫🇷, 🇵🇱, 🇰🇷, 🇧🇷, 🇨🇿, 🇬🇪.
• regexplained [GitHub] - Best tester for presentations (JavaScript).

Build regexes without writing regex syntax or code.

• ChatGPT (and other LLMs) - Ex: "create a regex that matches X and explain it step by step".
• RegexMagic (, $40) - Generate regexes using samples and rules.
  • Flavors: Emulates hundreds of flavors/versions.

Visualize how your regular expressions are structured or operate.

• Regex Vis [GitHub] - Create railroad diagrams, with visual editor. Flavor: JavaScript.
  • Languages: 🇺🇸, 🇨🇳.
• Regulex [GitHub] - Create railroad diagrams. Flavor: JavaScript.
• Nodexr [GitHub] - Graphical editor with visual hierarchy. Flavor: .NET.

Grep-like software.

Command line

• ripgrep - Better and faster grep. Recursively searches directories while respecting gitignore rules and skipping hidden/binary files.
  • Flavors: Rust (default), PCRE.

➕ See also: Feature comparison of grep-like tools.

GUI

• Aba Search and Replace (, $30) - Displays matches as you type.
• PowerGREP (, $159) - Can search through archives, binary files, PDFs, docs/sheets, emails, etc., via its GUI or the command line.
  • Flavors: Emulates hundreds of flavors/versions.
• RegexRenamer () - Rename files using regexes.

Learn how to use regular expressions.

Traditional

• Regular-Expressions.info - Covers numerous regex flavors.
• The Modern JavaScript Tutorial: Regular expressions [GitHub] - Guide to using regexes in modern JavaScript.
  • Languages: 🇺🇸, 🇪🇸, 🇫🇷, 🇮🇹, 🇯🇵, 🇷🇺, 🇺🇦, 🇨🇳 (partial for others).

With interactive exercises

• RegexLearn [GitHub] - Interactive tutorial and practice problems.
  • Languages: 🇺🇸, 🇹🇷, 🇷🇺, 🇪🇸, 🇨🇳, 🇩🇪, 🇺🇦, 🇫🇷, 🇵🇱, 🇰🇷, 🇧🇷, 🇨🇿, 🇬🇪.
• RegexOne - Interactive tutorial and practice problems.

Regex video tutorials.

• Demystifying Regular Expressions - Great presentation for beginners, by Lea Verou at HolyJS 2017 (1hr 12m).
• Learn Regular Expressions In 20 Minutes - Live syntax walkthrough in a regex tester, by Kyle Cook.
• Many options for video courses are available on Udemy ($).

Major regex implementations, built into programming languages or as standalone libraries.

Official regex references and guides.

Regex flavors

• JavaScript (MDN): RegExp, Reference, Guide.
• Boost.Regex: Manual.
• C++: Regular expressions library.
• Hyperscan: Introduction.
• ICU: Regular Expressions.
• Java: Pattern, API.
• .NET: Overview, Language, API.
• Onigmo: RE.
• PCRE: pcre2pattern, API.
• Perl: Syntax, Tutorial, Quick Start.
• Python: re.
• RE2: Syntax.
• Rust: regex, regex_lite.

ℹ️ Raku (formerly Perl 6) reimagines regexes. See: Grammars (tutorial), Regexes (best practices).

Without own flavor

• MySQL: Regular Expressions - Flavor: ICU.
• PHP: Regular Expressions - Flavor: PCRE.
• Ruby: Regexp - Flavor: Onigmo.
• Swift: NSRegularExpression - Flavor: ICU.

Read or contribute to the code behind major regex implementations.

• V8: Irregexp - JavaScript RegExp engine used by Chrome, etc.
• Boost.Regex - Popular C++ regex library.
• Hyperscan - Intel's high-performance library, used for DPI.
• ICU - Unicode org's package with full Unicode support.
• Java: java.util.regex - JDK standard regexes.
• .NET: System.Text.RegularExpressions - Shared by all .NET languages (C#, VB, etc.).
• Onigmo - Forked and extended from Oniguruma. Default regex library of Ruby 2.0+.
• Oniguruma - Popular C regex library. Default regex library of Ruby 1.9.
• PCRE2 - Popular C regex library used by PHP, R, etc.
• Perl - See perlreguts.
• Python: re and regex - Standard and extended regex libraries.
• RE2 - Popular C++ regex library used by Go, etc. Non-backtracking engine.
• Rust: regex - Non-backtracking engine.

Syntax and behavior differences between regex flavors.

• Ron Buckton: Regular Expression Feature Comparisons [GitHub].
• Regular-Expressions.info: Tools & Languages.
• Steven Levithan: Named capture, Lookbehind.
• Wikipedia: Comparison of regular expression engines.

Pattern and engine performance, benchmarks, and ReDoS prevention.

Crafting efficient regexes

• Runaway Regular Expressions: Catastrophic Backtracking - Exploration and solutions for superlinear backtracking.
• Book: High Performance JavaScript (2010) - Chapter 5: Strings and Regular Expressions.
• Book: Mastering Regular Expressions, 3rd Edition (2006) - Chapter 6: Crafting an Efficient Expression.
• Performance of Greedy vs. Lazy Regex Quantifiers - Illustrates the mechanics of backtracking.

ℹ️ With backtracking engines, how you craft a regex can affect how fast it finds matches or reports failures.

Regex engine optimizations

• Regular Expression Matching Can Be Simple And Fast - On non-backtracking engines. A follow up includes comparisons of RE2 and PCRE performance.
• Regular Expression Improvements in .NET 7 and .NET 5 - Includes detailed explanations of performance optimizations.
• ripgrep is faster than {grep, …} - Includes details about what makes ripgrep and Rust's regex fast.

Benchmarking

• Libraries for cross-engine benchmarking: rebar, regex-benchmark, sljit/regex_perf.html.
• Boost.Regex: Performance - Compares Boost, C++'s std::regex, and others.

ReDoS checkers

• recheck [home] - JavaScript and Scala library for detecting ReDoS vulnerability. Can be used as an ESLint plugin.
• vuln-regex-detector - Perl library for detecting ReDoS vulnerability.

Prewritten regexes for specific tasks.

• Book: Regular Expressions Cookbook, 2nd Edition (2012) - High-quality solutions with detailed explanations.
  • Flavors: Java, JavaScript, .NET, PCRE, Perl, Python, Ruby, XRegExp.
• Regex DB - Solutions include basic descriptions and examples of matching and non-matching text.

Open source JavaScript libraries for advanced regex use and processing.

Regex processors

• AST builders: regexp-tree (includes optimizer, etc.), regexpp (used by ESLint).
• Generate strings that match a given regex: randexp.js, regex-to-strings.
• Generate a regex from given strings: regexgen.
• Highlight regex syntax: Regex Colorizer [home], CodeMirror PCRE mode.
• Find regex mistakes and stylistic improvements: eslint-plugin-regexp [home].

Alternative regex builders and engines

• XRegExp [home] - Extended regex syntax, flags, and utils.
• String template tags: regexp-make-js, XRegExp.tag.
• incr-regex-package - Partial/incremental matching, used by react-rxinput for input validation with a regex mask.
• @iter-tools/regex - Non-backtracking engine for streaming evaluation.

Readable regex composers

• Rexx - Structured syntax with variables and comments.
• compose-regexp.js - Compose with functions. Includes extra regex features like atomic, bound.
• More: VerbalExpressions (has implementations for many languages), magic-regexp [home], Super Expressive [playground], Melody [docs].

A concise history of improvements to regular expressions in the JavaScript standard, with links to the TC39 proposals where features were developed and discussed.

• ES3 (1999) introduced powerful regular expressions, though limited compared to other major flavors.
• ES5 (2009) fixed unintuitive behavior by creating a new object every time regex literals are evaluated [explainer], and allowed regex literals to use unescaped forward slashes within character clases (/[/]/).
• ES6/ES2015 added: [explainer]
  • Flag y (sticky), which anchors matches to lastIndex.
  • Flag u (unicode) [explainer] [2016 spec fix] with errors for unreserved letter escapes, Unicode code point escapes (\u{…}), impact on flag i, and surrogate pairs as code points (with impact on quantifiers, character classes, character class ranges, and built-in classes like . and \W).
  • Getter RegExp.prototype.flags.
  • Can subclass RegExp, plus RegExp.prototype[Symbol.match/replace/search/split] and RegExp[Symbol.species] for use in subclasses.
  • Use RegExp to copy a regex, optionally with new flags.
• ES2018 added flag s (dotAll), lookbehind, named capture, and Unicode properties via \p{…} and \P{…} behind flag u (see property list).
• ES2020 added string method matchAll (which returns an iterator) and RegExp.prototype[Symbol.matchAll].
• ES2021 added replaceAll.
• ES2022 added flag d (hasIndices), which provides start/end indices for matched substrings.
• ES2024 added flag v (unicodeSets) [explainer] as an upgrade to flag u (can't be used together); adds properties of strings to \p{…}, multicharacter elements within character classes via \p{…} and \q{…|…}, nested character classes, set operators […--…] and […&&…], improved case-insensitive matching, and different escaping rules within character classes.

A curated list of regex books.

• Regular Expressions Cookbook, 2nd Edition (2012) by Jan Goyvaerts and Steven Levithan - Regex tutorial with code samples for eight programming languages, 100+ regex recipes for practical problems, and a deep focus on cross-flavor differences.
  • Flavors: Java, JavaScript, .NET, PCRE, Perl, Python, Ruby, XRegExp.
• Mastering Regular Expressions, 3rd Edition (2006) by Jeffrey Friedl - A computer science classic, best for people who already know the basics. Includes good coverage of crafting efficient regexes.
  • Flavors: Dedicated chapters on Java, .NET, Perl, and PHP (PCRE), with more limited coverage of Python, Tcl, command line tools, etc.
• Introducing Regular Expressions (2012) by Michael Fitzgerald - An intro for programmers new to regular expressions that sticks to the basics.

A curated list of regex articles.

• The World's Shortest Regex Compiler? and a follow up on optimization - Introduction to writing a non-backtracking regex engine (in JavaScript).
• Regex Legends: The People Behind the Magic - Influential people behind the technology.
• Fun With .NET Regex Balancing Groups - Advanced usage of a .NET-only regex feature.

Discuss, assist, and get help with regular expressions.

• Reddit: r/regex
• Stack Overflow: [regex]

Other interesting, fun, and useful stuff.

• Chrome extension: Regex - Regex search on webpages via Ctrl+Shift+F.
• Games: Regex Crossword, Redoku.
• Comics: xkcd, Garabato Kid.