# regexguide.com

> A free, in-browser regex explainer and pattern library. Paste any regular expression and get a plain-English, token-by-token breakdown; browse 300 tested patterns; and learn regex through guides, a glossary, and a 100+ question FAQ. Everything runs client-side — no signup, no upload, and no tracking of your regex content.

## Tools
- [Regex Explainer](https://regexguide.com/index.html#tool): Paste a regex, get a token-by-token plain-English explanation, live testing against your input, and generated code in 7 languages.
- [English → Regex](https://regexguide.com/from-english.html): Describe a pattern in plain English and get a regex. Rule-based and deterministic (not AI).
- [Flavor Converter](https://regexguide.com/convert.html): Convert a regex between JavaScript, Python, Java, .NET, Go, Ruby, and PCRE.
- [Visual Editor](https://regexguide.com/visual-editor.html): Build a regex by stacking configurable blocks.
- [Cheat Sheet](https://regexguide.com/cheat-sheet.html): One-page reference of every regex token, character class, group, anchor, and flag.

## Reference
- [Pattern Library — 300 patterns](https://regexguide.com/patterns.html): Tested regex patterns for validation, extraction, and parsing. Each has a token breakdown, tailored pitfalls, usage in 7 languages, authoritative sources, and a downloadable PDF cheat sheet.
- [Regex Glossary — 116 terms](https://regexguide.com/glossary.html): Definitions of regex terminology, with authoritative sources (RFC, Unicode, PCRE, POSIX).
- [FAQ — 100+ questions](https://regexguide.com/faq.html): The most-searched regex questions answered, with FAQPage structured data.

## Guides
- [Anchors and boundaries — pinning regex to specific positions](https://regexguide.com/guides/anchors.html)
- [Capture groups — every kind explained](https://regexguide.com/guides/capture-groups.html)
- [Advanced character classes](https://regexguide.com/guides/character-classes-advanced.html)
- [Character classes — the most expressive part of regex](https://regexguide.com/guides/character-classes.html)
- [The 10 mistakes that ruin most regex](https://regexguide.com/guides/common-mistakes.html)
- [Escaping special characters](https://regexguide.com/guides/escape-characters.html)
- [Regex flags deep dive](https://regexguide.com/guides/flags-deep-dive.html)
- [Groups and capture groups](https://regexguide.com/guides/groups-and-captures.html)
- [Lookaheads and lookbehinds — zero-width assertions](https://regexguide.com/guides/lookarounds.html)
- [Greedy vs lazy vs possessive — the three flavors of "more than one"](https://regexguide.com/guides/quantifiers.html)
- [Validating Indian IDs with regex](https://regexguide.com/guides/regex-aadhaar-pan.html)
- [Converting regex between flavors](https://regexguide.com/guides/regex-converting-flavors.html)
- [Regex flags — what each one does](https://regexguide.com/guides/regex-flags-complete.html)
- [Regex fundamentals — from zero to confident](https://regexguide.com/guides/regex-fundamentals.html)
- [Regex in Go](https://regexguide.com/guides/regex-in-go.html)
- [Regex in Java](https://regexguide.com/guides/regex-in-java.html)
- [Regex in JavaScript](https://regexguide.com/guides/regex-in-javascript.html)
- [Regex in C# / .NET](https://regexguide.com/guides/regex-in-net.html)
- [Regex in Python](https://regexguide.com/guides/regex-in-python.html)
- [Regex performance](https://regexguide.com/guides/regex-performance.html)
- [Regex substitution — search and replace with back-references](https://regexguide.com/guides/regex-substitution.html)
- [Validation regex patterns — and what not to do](https://regexguide.com/guides/regex-validation-patterns.html)

## Blog
- [Regex backreferences — match the same text twice](https://regexguide.com/blog/backreferences.html)
- [Regex case insensitive — in every language](https://regexguide.com/blog/case-insensitive-regex.html)
- [10 more common regex mistakes (and how to fix them)](https://regexguide.com/blog/common-regex-mistakes-2.html)
- [How to escape special characters in regex](https://regexguide.com/blog/escape-special-characters.html)
- [Extract the file extension from a filename with regex](https://regexguide.com/blog/extract-file-extension.html)
- [Extract @mentions and #hashtags from a tweet](https://regexguide.com/blog/extract-mentions-hashtags.html)
- [How to extract numbers from text with regex](https://regexguide.com/blog/extract-numbers-regex.html)
- [Extract Indian PAN numbers from a document — Python and JavaScript](https://regexguide.com/blog/extract-pan-from-text.html)
- [Extract international phone numbers from text](https://regexguide.com/blog/extract-phone-international.html)
- [Extract URLs from a block of text with regex](https://regexguide.com/blog/extract-urls-from-text.html)
- [Find duplicate consecutive words with regex](https://regexguide.com/blog/find-duplicate-words.html)
- [Greedy vs lazy quantifiers in regex](https://regexguide.com/blog/greedy-vs-lazy-quantifiers.html)
- [Lookahead vs lookbehind — when to use each](https://regexguide.com/blog/lookahead-vs-lookbehind.html)
- [Mask all but the last 4 digits of a credit card number](https://regexguide.com/blog/mask-credit-card.html)
- [Regex match anything except specific characters](https://regexguide.com/blog/match-anything-except.html)
- [Match content between two delimiters with regex](https://regexguide.com/blog/match-between-delimiters.html)
- [Regex to match anything between two strings](https://regexguide.com/blog/match-between-two-strings.html)
- [Regex to match a date — every common format](https://regexguide.com/blog/match-date-regex.html)
- [Match dates in different formats — ISO, US, EU, and more](https://regexguide.com/blog/match-dates-in-formats.html)
- [How to match an email address with regex (and why no regex is truly perfect)](https://regexguide.com/blog/match-email-regex.html)
- [Strict IPv4 address regex (with octet range validation)](https://regexguide.com/blog/match-ipv4-strict.html)
- [Match quoted strings (with escape handling)](https://regexguide.com/blog/match-quoted-strings.html)
- [How to match a URL with regex](https://regexguide.com/blog/match-url-regex.html)
- [Regex match multiline — the dotall flag explained](https://regexguide.com/blog/multiline-dotall-flag.html)
- [Regex named groups in JavaScript and Python](https://regexguide.com/blog/named-groups.html)
- [What does (?:) mean in regex? Non-capturing groups explained](https://regexguide.com/blog/non-capturing-groups.html)
- [Python regex vs JavaScript regex — 7 differences that matter](https://regexguide.com/blog/python-vs-javascript-regex.html)
- [The pocket regex cheat sheet (bookmark this)](https://regexguide.com/blog/regex-cheatsheet-bookmark.html)
- [Every regex flag in every language — full reference](https://regexguide.com/blog/regex-flags-cheat-sheet.html)
- [Remove emojis from a string with regex](https://regexguide.com/blog/remove-emojis.html)
- [Replace multiple spaces with a single space](https://regexguide.com/blog/replace-multiple-spaces.html)
- [Why is my regex slow? Common causes and fixes](https://regexguide.com/blog/slow-regex.html)
- [Parse a CSV line — when regex works and when it doesn't](https://regexguide.com/blog/split-csv-line.html)
- [Strip HTML tags from a string with regex](https://regexguide.com/blog/strip-html-tags.html)
- [How to validate an Aadhaar number with regex (Python)](https://regexguide.com/blog/validate-aadhaar-python.html)
- [How to validate phone numbers with regex](https://regexguide.com/blog/validate-phone-number.html)
- [Validate a strong password with regex](https://regexguide.com/blog/validate-strong-password.html)
- [What does \b mean in regex?](https://regexguide.com/blog/what-does-b-mean-in-regex.html)
- [What is ReDoS? Regex denial-of-service explained](https://regexguide.com/blog/what-is-redos.html)

## About
- [About regexguide.com](https://regexguide.com/about.html)
- [How it works](https://regexguide.com/howitworks.html)
- [Contact](https://regexguide.com/contact.html)