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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
• Grep-like tools
• Tutorials
• 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.

Search and replace through files.

• 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.

• 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.

• 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).

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

• 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.

• 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).

• 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, Edge, Firefox, etc.
• JavaScriptCore: RegExp - JavaScript RegExp engine used by Safari.
• 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.

• 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.

• 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.

• Cross-engine benchmarking libraries: rebar, regex-benchmark.
• Boost.Regex: Performance - Compares Boost, C++ std::regex, and others.

• regex.rip - Test a regex for ReDoS vulnerability.
• 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.

⚠️ These tools have limitations on supported syntax.

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 - Context-aware regex template tag with advanced features and best practices built-in.
• XRegExp [home] - Extended regex syntax, flags, and utils; useful for backcompat.
• incr-regex-package - Partial/incremental matching, used by react-rxinput for input validation with a regex mask.
• node-re2 - Bindings for RE2, a non-backtracking engine.
• rregex - Bindings for Rust's regex, a non-backtracking engine.

• Rexx - A template tag that uses structured syntax with variables and comments.
• Melody [docs] - A language that compiles to regexes.
• Compose with functions: compose-regexp.js, VerbalExpressions (implementations for many languages), magic-regexp [home], Super Expressive [playground].

• AST builders: regexp-tree (includes optimizer, etc.), regexpp (used by ESLint), regjsparser/regjsgen.
  • AST Explorer: RegExp - View ASTs generated by regexp-tree, regexpp, and regjsparser.
  • regexp-ast-analysis [docs] - Analyze AST nodes produced by regexpp.
• Highlight regex syntax: Regex Colorizer [home], CodeMirror PCRE mode.
• Find regex mistakes and improvements: eslint-plugin-regexp [home], eslint-plugin-optimize-regex.
• Generate strings that match a given regex: randexp.js, regex-to-strings.
• Generate a regex from given strings: regexgen.

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], which adds Unicode code point escapes via \u{…}, strict errors (for unreserved letter escapes, octal escapes, escaped literal digits, and unescaped special characters in some contexts), Unicode case-folding for flag i, and code-point-based matching (with impact on quantifiers, character classes, character class ranges, and built-in sets 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 list).
• ES2020 added string method matchAll (which returns an iterator), plus RegExp.prototype[Symbol.matchAll].
• 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), which adds a set of multicharacter "properties of strings" to \p{…}, multicharacter elements within character classes via \p{…} and \q{…|…}, nested character classes, set operators […--…] and […&&…], and different escaping rules within character classes. It also fixes case-insensitive matching for doubly-negated [^\P{…}].

Each edition from ES2019 to ES2023 added additional Unicode properties that can be used via \p{…} and \P{…} (see lists). ES2021 added replaceAll, which optionally accepts a RegExp, but it behaves identically to ES3's replace when given a regex as the search.

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.
• Quiz: regex101 Regex Quiz - Requires sign-in.
• Games: Regex Crossword, Redoku.
• Comics: xkcd, Garabato Kid.