FeaturedRegEx
Top 5 Online Regex Testers for 2026
The five online regex testers I actually use, ranked: Regex101, RegExr, RegexPlanet, Debuggex, and Rubular. What each is good at, where each falls short, and which flavor each one supports.
Topic · RegEx
RegEx
Patterns that match what you mean, even when the input doesn't.
20 articlesWritten by Ishan Karunaratne
More in RegEx
How to Use Regex in Nginx (location and rewrite)
Use regex in Nginx with location blocks and the rewrite directive: how location modifiers and matching priority work, why return beats rewrite for redirects, and copy-paste config for HTTPS, www, trailing slashes, 301s, clean URLs, and access blocking.
How to Use Regex in .htaccess (Apache mod_rewrite)
Use regex in .htaccess with Apache mod_rewrite: how RewriteRule and RewriteCond patterns work, the per-directory quirk that breaks everyone, and copy-paste rules for HTTPS, www, trailing slashes, 301s, clean URLs, and access blocking.
How to Use Capturing Groups and Backreferences in Regex
Capturing groups, named groups, non-capturing groups, and backreferences in regex. JavaScript / Python / PHP examples, engine notes, common mistakes, and the duplicate-word and swap-fields use cases.
The Regex (*ACCEPT) Control Verb, Explained
What the PCRE (*ACCEPT) backtracking control verb does, how it forces an immediate successful match, how it behaves inside capturing groups, which engines support it, and where it is genuinely useful.
How to Use Regex Lookaheads and Lookbehinds
Regex lookaheads and lookbehinds assert what comes before or after a match without consuming characters. Full reference with syntax, password validation, variable-width vs fixed-width support per engine, and examples in JavaScript, Python, PHP, Go, Java, .NET.
How to Match a Date with Regex (Multiple Formats)
Match a date with regex in ISO 8601, US, EU, and relaxed formats. Month/day validation, leap-year notes, JavaScript / Python / PHP examples, engine notes, common mistakes.
How to Match a Domain Name with Regex
Match a domain name with regex. Basic labels, RFC 1035 length rules, subdomains, IDN punycode, trailing-dot form, JavaScript / Python / PHP examples, engine notes, and common mistakes.
How to Match an Email Address with Regex
Match an email address with regex. The practical pattern, the strict RFC 5321 pattern, examples in JavaScript, Python, and PHP, edge cases, engine compatibility, common mistakes, and a validation test table.
How to Match a Hex Color Code with Regex
Match a hex color code with regex. 3-digit, 6-digit, and 8-digit (alpha) forms. JavaScript / Python / PHP examples, engine notes, common mistakes, a stripped-hash variant.
How to Match HTML Tags with Regex (And Why You Probably Shouldn't)
Match HTML tags with regex when you must, and the case for parsing instead. Patterns for opening, closing, self-closing, attribute-bearing tags, JavaScript / Python / PHP, engine notes, common mistakes.
How to Match an IPv4 and IPv6 Address with Regex
Match an IPv4 or IPv6 address with regex. Octet-bounded IPv4, compressed and full IPv6, CIDR, IPv4-mapped IPv6, parser fallback, engine notes, and common mistakes.
How to Match Numbers with Regex
Match integers, decimals, signed, scientific, thousands-separated, currency, and percent numbers with regex. JavaScript / Python / PHP examples, engine notes, common mistakes, test table.
How to Match a URL with Regex
Match a URL with regex. Covers http/https schemes, protocol-relative URLs, ports, paths, query strings, fragments, runnable JavaScript / Python / PHP, engine notes, and the URL parser alternative.
How to Validate a Credit Card Number with Regex
Validate a credit card number with regex. Visa, MasterCard, Amex, Discover, Diners, JCB patterns, plus the Luhn checksum, JavaScript / Python / PHP examples, engine notes, common mistakes.
How to Validate a US Phone Number with Regex
Validate a US phone number with regex. The practical pattern, a stricter NANP version, runnable examples in JavaScript, Python, and PHP, what it still lets through, common mistakes, and a test table.
Regex Anchors
Regex anchors are unique tokens that assert positions within a string without matching characters. Discover their role in pattern matching across languages.
Regex Cheat Sheet
Regex Cheat Sheet including regex symbols, ranges, grouping, assertions, syntax tables, examples, matches, and compatibility tables. Definitive Regular Expressions Quick Reference!
How to Validate Password Strength with Regex
Validate password strength with regex. Length checks, character-class requirements, lookahead patterns for mixed-case/digit/special enforcement, examples in JavaScript, Python, and PHP, engine notes, and common mistakes.
Regex Word Boundaries: \b, \B, and Lookaround Equivalents
Regex word boundaries (\b and \B) match positions between word and non-word characters with zero width. The full reference with engine differences, Unicode handling, lookaround alternatives, and worked examples for whole-word replace, search highlighting, and log parsing.