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Awesome Regex

Awesome  Shortcut URL: regex.cool

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.

📖 Glossary

A brief glossary of regular expression terms as used in this list.

  • Regex engine: Software that interprets and executes regular expressions, either built into a programming language or as a standalone library.
  • Regex flavor: A unique set of regex syntax and behavior. Basic syntax is typically shared across flavors, but more advanced features often vary, sometimes in subtle or incompatible ways. A flavor might be shared across multiple implementations or programming languages.
    • Ex: The “JavaScript” flavor is defined by the ECMAScript spec; implemented by multiple engines (V8, etc.).
    • Ex: The “PCRE” flavor is the PCRE2 library, used by numerous programming languages and tools.
    • Ex: Ruby swapped its regex implementation twice from version 1.8 ➜ 1.9 ➜ 2.0, so each used a distinct flavor. The Ruby 2.0+ flavor is referred to here as either “Ruby” or “Onigmo” (the underlying regex library).
  • Non-backtracking engine: A regex implementation that uses a non-backtracking algorithm and runs in linear time. This rules out worst case performance from superlinear backtracking, but it's slower with some patterns and precludes some useful features like backreferences.

Contents

Testers

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).
✳️ Notable mentions

Flavors

Multiple flavors

  • CyrilEx [GitHub] - Java, JavaScript, MySQL, PHP, Python, Ruby.
  • Patterns (, $3) - Bash, Emacs, grep, Java, Oniguruma, PCRE, POSIX BRE, POSIX ERE, Ruby, sed.
  • RegexPlanet [GitHub] - Go, Haskell, Java, JavaScript, .NET, Perl, PHP, PostgreSQL, Python, Ruby, Tcl, XRegExp.

Syntax-free regex builders

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.
✳️ Notable mentions
  • Regex Generator [GitHub] - Generate simple regexes from a sample text.
  • Regex.ai - Mark samples in a text and use AI to generate potential regexes.

Visualizers

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.
✳️ Notable mentions
  • Regex Nodes [GitHub] - Graphical editor with visual hierarchy. Flavor: JavaScript.
  • Debuggex - Create railroad diagrams. Flavors: JavaScript, PCRE, Python.
  • Regexper [GitLab] - Create railroad diagrams. Flavor: JavaScript.

Grep-like tools

Search and replace through files.

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.
  • PowerRename () - Rename files using regexes.

Tutorials

Learn how to use regular expressions.

Traditional

✳️ Notable mentions

With interactive exercises

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

Videos

Regex engines

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

Documentation

Official regex references and guides.

Regex flavors

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

Without own flavor

Source code

Read or contribute to the code behind major regex implementations.

Flavor differences

Syntax and behavior differences between regex flavors.

Performance

Pattern and engine performance, benchmarks, and ReDoS prevention.

Crafting efficient regexes

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

✳️ Notable mentions

Regex engine optimizations

Benchmarking

ReDoS checkers

  • 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.

Collections of patterns

Prewritten regexes for specific tasks.

⚠️ Word of warning

Many regexes found online are low quality. It's risky to use regexes you don't fully understand in code, since they might have false positives/negatives, be vulnerable to performance problems with certain target strings, or assume a different regex flavor.

JavaScript regex libraries

Open source JavaScript libraries for advanced regex use and processing.

Alternative regex builders and engines

  • 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.

Abstracted regex syntax

Regex processors

JavaScript regex evolution

The history of improvements to regular expressions in the JavaScript standard. Starting with ES2018, includes links to the TC39 proposals where features were developed and discussed.

  • ES3 (1999) introduced regular expressions.
  • 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 classes (/[/]/).
  • 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 escapes, octal escapes, quantified lookahead, and unescaped special characters in some contexts), Unicode case-folding for flag i, and code point matching (with impact on quantifiers, character classes, ranges, and built-in sets).
    • Getter RegExp.prototype.flags, the ability to copy a regex using RegExp (optionally with new flags), and support for subclassing RegExp (along with RegExp.prototype[Symbol.match/replace/search/split] and RegExp[Symbol.species]).
  • ES2018 added flag s (dotAll), lookbehind, named capture, and Unicode properties (via \p{…} and \P{…} which require 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, 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 \p and \P within negated [^…].

Each edition from ES2019 to ES2023 added additional Unicode properties that can be used via \p{…} and \P{…} (see lists). ES2021 added string method replaceAll, although, when given a regex, the only difference from ES3's replace is that it throws if not using flag g.

See also
🔮 Future: Active proposals

Books

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.

Articles

A curated list of regex articles.

Communities

Discuss, assist, and get help with regular expressions.

Miscelaneous

Other interesting, fun, and useful stuff.

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