All tools on RegexCalc
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RegexCalc (main tool)
Free, instant client-side regular expression tester and calculator. Match highlighting, group capture extraction, and common pattern recipes.
Regex Replace Tester
Test JavaScript regex replacements live with $1 to $99, named groups, $&, $` and $', and literal $ escaping, computed by your browser's own replace(), with shareable links.
Regex Explainer
Paste a regular expression and get every token explained, plus warnings measured live in your own browser engine: greedy vs lazy, capture-group count, unicode-flag breakage, and anchoring traps.
Email Regex Pattern & Tester
A practical email regex for sign-up forms, tested live in your browser, with a table of the addresses it accepts and rejects and where it is looser or stricter than RFC 5322.
Phone Number Regex (E.164 & US Formats)
Test a phone number regex that covers compact E.164 numbers and US formats, with a table of the inputs it accepts and rejects, including the spaced international numbers it misses.
IPv4 Address & CIDR Regex Pattern
An IPv4 regex that limits each octet to 0-255 and allows an optional /0 to /32 CIDR suffix, tested live, with a table of edge cases including the leading-zero trap.
URL Regex Pattern (http & https)
Test an http and https URL regex with ports, paths, query strings and fragments, and see the edge cases it rejects: localhost, upper-case schemes and Unicode hosts.
UUID v4 Regex Pattern & Validator
A UUID version 4 regex that checks the version and variant digits, tested live, with a table of what it rejects: upper case, other versions, the nil UUID and braces.
Looking for explanations rather than a tool? RegexCalc guides cover 13 worked examples and gotchas.
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